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A VLA study of 24 short term radio variables Pőller, Bernard J. 1997

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A V L A S T U D Y O F 2 4 S H O R T T E R M R A D I O V A R I A B L E S Bernard J . Poller B. Sc. (Physics) Dalhousie University, 1995 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R - O F S C I E N C E in T H E F A C U L T Y O F G R A D U A T E S T U D I E S D E P A R T M E N T O F P H Y S I C S A N D A S T R O N O M Y We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 1997 © Bernard J . Poller, 1997 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Physics and Astronomy The University of British Columbia 6224 Agricultural Road Vancouver B .C . Canada V6T 1Z1 Date: Abstract Flux density variability information, on a time scale of days, has been extracted [2] for a number of radio sources, from the GB6 [1] catalog data. Twenty four sources, including some with NVSS counterparts, exhibiting significant short term variability, and with no current identification in either the NED or SIMBAD external databases, were selected for a Very Large Array B configuration study. V L A snapshots were taken at two epochs, separated by approximately a month, at two frequency bands, to elucidate variations in flux density, source structure and spectral index. The imaged sample of twenty four sources include well resolved sources with one-sided or two-sided structure, partially resolved sources, and some unresolved sources. Of the partially resolved and unresolved sources, a number are confirmed as being variable in flux density and spectral index. In particular, the partially resolved sources J l 700+685, J2115+367, and J2145+187 exhibit short term structural variation, suggesting these sources are galactic. The unresolved sources J0251+562, J0502+346, and J0611+723 exhibit significant flux variability. APS results indicate that the unresolved source J0856+717 is stellar. i i Table of Contents Abstract ii Table of Contents iii List of Tables vi List of Figures vi i Acknowledgements x 1 Introduction to Radio Variability 1 1.1 The Green Bank 6 Centimeter Survey 2 1.2 The Short Term Radio Variable V L A Study 3 1.3 Measures of Variability 4 2 Radio Variabil ity Mechanisms 6 2.1 Active Galactic Nuclei 6 2.1.1 Unification Schemes 7 2.1.2 Relativistic Effects 7 2.2 Galactic Jet Sources 10 2.3 Radio Stars 15 2.4 Interstellar Scintillation 16 3 G B 6 Long T e r m Variability 2 0 3.1 Galactic Projection and Variability Index Dependence 20 ii i 3.2 Spectral Index Fraction Density 3.3 Variability Fraction Density . . 22 25 4 GB6 Short Term Variability 30 4.1 Q Value Statistics and Selection 30 4.2 External Database Search 32 4.2.1 N R A O V L A Sky Survey 34 4.2.2 SIMBAD and NED Databases 35 4.2.3 APS Optical Counterparts 36 4.3 Selected Variable Sources for V L A Study 38 5 Radio Imaging with the V L A 51 5.1 Interferometry and Aperture Synthesis 51 5.2 V L A parameter selection 55 5.3 Imaging with AIPS 57 6 Results and Conclusion 60 6.1 Resolved Sources 60 6.1.1 Two-Sided Sources 68 6.1.2 One-Sided Sources 74 6.2 Partially Resolved Sources 76 6.3 Unresolved Sources 77 6.4 APS and DSS Optical Counterparts 77 6.5 Conclusion 79 Bibliography 86 A Short Term Variable Tables 88 iv A . l Short Term Variable Positions 88 A.2 Short Term Variable Flux Related Information 94 A.3 Short Term Variable SIMBAD Matches 99 A.4 Short Term Variable NED Matches 101 A.5 Short Term Variable APS Counterparts 105 v List of Tables 4.1 Selected Source Position Information 41 4.2 Selected Source Flux Related Information 42 4.3 Selected Source Database Information 43 5.1 V L A Parameters in B Configuration 56 6.1 Image quality information for sources observed with the V L A 67 6.2 Measured parameters of two-sided resolved sources 70 6.3 Measured parameters of one-sided resolved sources 75 6.4 Measured parameters of partially resolved sources 78 6.5 Measured parameters of unresolved sources 79 6.6 DSS optical counterparts of imaged radio sources 80 6.7 APS determined parameter of DSS POSS I optical counterparts of imaged radio sources 80 6.8 Summary of characteristic parameters for V L A imaged radio sources. . . 81 vi List of Figures 2.1 V L A image of radio galaxy 3C219 . 8 2.2 Plot of Doppler factor 11 2.3 Schematic representation of SS433 12 2.4 V L A radio maps of microquasar GRS1915+105 13 2.5 Angular displacement of GRS1915+105 versus 3.5 cm flux density and time since ejection 14 2.6 Scintillation index and time scale 18 2.7 Flux density of ISS source 0917+624 at 6 cm 19 3.1 Galactic projection of GB6 long term variable sources 21 3.2 Variability index versus galactic latitude for GB6 long term variables. . . 22 3.3 Fraction density versus spectral index for GB6 long term variables and GB6 catalog 23 3.4 Spectral index centroid versus GB6 flux, sigma confidence level, and vari-ability index 26 3.5 GB6 fraction density versus sigma confidence level 27 3.6 GB6 variability index selection factor 28 3.7 Plot of computed, and model of, GB6 fraction density and cumulative fraction as a function of variability index 29 4.1 Galactic projection of short term variability list with short term variables highlighted 31 4.2 Normalized density of sources versus short term variability 33 vii 4.3 Scatter plots of 1986 versus 1987 epoch short term variability and short term variability versus long term variability confidence level 34 4.4 Normalized density of APS matched short term variability sources as a function of magnitude and colour 38 4.5 Galactic distribution of short term variables selected for V L A study. . . . 40 4.6 Plot of daily flux density measurements for J0048+684, J0049+343, J0251+562, and J0259+516 44 4.7 Plot of daily flux density measurements for J0502+346, J0502+388, J0532+562, and J0611+723 45 4.8 Plot of daily flux density measurements for J0856+717, J0903+636, J1106+282, and J1307+064 46 4.9 Plot of daily flux density measurements for J1603+110, J1630+741, J1700+685, and J1814+228 47 4.10 Plot of daily flux density measurements for J1924+286, J1956+635, J2055+613, and J2115+367 48 4.11 Plot of daily flux density measurements for J2145+187, J2152+653, J2202+292, and J2208+615 49 5.1 Overhead view of V L A in D configuration 52 5.2 Close up view of a V L A antenna 53 6.1 V L A images of J0049+343 at X and U band 61 6.2 V L A images of J0259+516 at X band 62 6.3 V L A images of J0532+562 at X and U band 63 6.4 V L A images of J0903+636 at X band 64 6.5 V L A images of J1307+064 at X and U band 65 6.6 V L A images of J1630+741 at X and U band 66 viii 6.7 V L A images of J1700+685 at X band 68 6.8 V L A images of J1956+635 at X and U band 69 6.9 V L A images of J2115+367 at X band 71 6.10 V L A images of J2145+187 at X and U band 72 6.11 V L A images of J2202+292 at X and U band 73 ix Acknowledgements First and foremost I would like to thank my supervisor, Dr. Philip C. Gregory (UBC) who graciously provided support, encouragement, and guidance throughout this project, yet allowed me freedom in pursuing my masters thesis research. His years of research and many discoveries in the fields of radio and X-ray astronomy have been an inspiration, and his work on radio variability, particularly in the GB6 catalog, is the foundation for my research. I am greatly indebted to Dr. Gregory and this thesis would not have been possible without his help. I wish to thank Dr. Pat Murphy at N R A O for his invaluable assistance in installing the AIPS software package on our new L I N U X system. Without his expertise, the research would have come to a screeching halt, and there would have been no end to my computer frustrations. Finally, I would like to acknowledge all the faculty, staff, and students in the Physics and Astronomy Department at the University of British Columbia who supported me, and made my time at U B C memorable. x Chapter 1 Introduction to Radio Variability The study of variability in observed phenomena is a common focus of research in many fields of science. As humans, we are often fascinated by change, and endeavouring to understand it has led to numerous interesting discoveries. From a cosmological point of view, we know the universe and everything in it is continually evolving, yet on time scales of a lifetime the night sky appears, to first order, static. Significant astrophysical variability, on short time scales, is relatively rare as it usually implies, in the context of typical cosmic distances, violent, high energy processes with enormous power outputs, confined to small volumes of space. These dynamic events give us great astronomical insight, often eluding simplistic conventional wisdom and thereby challenging the formulation of new theories, in some of the most fundamental and interesting branches of physics. There are many examples of optical variability such as pulsating Cepheids used as cosmological distance indicators, to punctuated, cataclysmic events like supernovae, dur-ing which a star may become billions of times more luminous [19]. Variability at radio wavelengths is a relatively new field of study, and in this thesis, after an introduction, we begin by discussing mechanisms of variability in chapter 2. Long term GB6 variability is looked at in chapter 3 and in chapter 4 a sample of short term GB6 variables is presented, the short term variable selection process is outlined, and a summary of GB6 and external database information for the selected sources is given. A brief overview of V L A imaging is included in chapter 5 and the results of the V L A study are presented and discussed in 1 Chapter 1. Introduction to Radio Variability 2 chapter 6. 1.1 The Green Bank 6 Centimeter Survey Until recently, variability at radio wavelengths on a statistical, or survey basis had not been given the attention it deserved, the focus having been close monitoring of known radio variables. Little was known about the radio source population as a whole in terms of the fraction of sources variable at some level or on some time scale. A group of researchers from the University of British Columbia (UBC) and the Na-tional Radio Astronomy Observatory (NRAO) undertook a project, in the late 1980's, to survey the sky of the northern hemisphere for radio sources, particularly for variable sources. This project was completed, using the former 91 meter radio telescope in Green Bank, West Virginia, by surveying the sky between declinations 0 and 75 degrees at a wavelength of 6 centimeters (4.85 GHz), during November 1986 and October 1987. The radio source data available from this project fall into three main categories of astronomical interest. Radio images of the northern sky were constructed from the 1986 and 1987 epoch data. These images were combined and analyzed to yield position and average flux density information for 75,162 discrete sources with flux densities F > 18 mJy and angular diameters 4> < 10.5 arcminutes [1]. The published Green Bank 6 centimeter survey (GB6) includes source data, as well as specific catalog production information [1]. Based on the individual epoch maps, flux densities for both epochs were determined for sources stronger than « 25 mJy [1], yielding long term variability information, on a time scale of a year. To ensure sufficient sampling at lower declinations, the continuous scanning technique, as outlined in [2], over sampled higher declination sources. During each month long observing epoch, multiple flux density measurements, for all sources in the GB6 catalog, Chapter 1. Introduction to Radio Variability 3 were taken (typically six measurements per epoch) and therefore allow derivation of short term variability information on time scales from days to weeks. Extraction of short term variability information from the GB6 data is still in progress, with only a fraction of this information currently available. 1.2 The Short T e r m Radio Variable V L A Study With the available GB6 variability data, the next natural step was a more detailed follow up study of the more extreme short term variables at a higher resolution. The author undertook the project of selecting 24 suitable short term variables, and imaging these sources at two frequency bands and at two epochs with the Very Large Array (VLA) . With the GB6 short term variability information available at the project inception, sources ex-hibiting significant flux density variation and with no known identifications, were chosen. The selection process and the database resources used are discussed in more detail in section 4.1 and section 4.2. The goal of the project was to gain more information about these short term variables from accurate flux density measurements and high resolution intensity maps, perhaps elucidating the type of object involved. It was hoped that due to the extreme variability, some of the short term variables may be galactic relativisti-cally beamed jet sources or other galactic sources of interest. If the high resolution V L A images show evidence of significant structural change over the two epochs, this would strongly suggest a galactic object. By imaging at two frequencies we were able to obtain spectral index data to compliment the two epoch flux density measurements from which we derived month time scale variability information. Specific V L A imaging parameter information may be found in section 5.2. Chapter 1. Introduction to Radio Variability 4 1.3 Measures of Variability Before studying variability one must first be able to quantify variation, and in the context of this thesis, we are primarily concerned with measuring variations in flux density. The flux density of a variable object may be considered to be continuously changing, with some amplitude, for a superposition of time scales. Both the amplitude and time scales of variation may be functions of time themselves. Intrinsically, measurements are limited by number, frequency, and duration of observation, and therefore the data are merely a statistical sample valid only for a specific range of time scales. Analysis of variability is complicated further by measurement uncertainties inherent in all experiments. There are a number of ways to quantify observed variability, each with it's own merit. In the simplest case two measurements, Fi and F 2 , with associated uncertainties, o\ and cr2, are taken a time, At, apart. If we define the flux density change A F as \Fi — F 2 | then we can compute a variability index, V, given by or in terms of a weighted average value and expressed as a percentage A F V% = x 1 0 0 (1 .2 ) w where * . = ( * + * ) , ( ! + ! ) . ( 1 . 3 ) \Oi CT2 / W l CF2J Both equation 1.1 and 1.2 are good measures of the level of variation, but do not directly incorporate error estimates. A sigma confidence level, Va, for a detected variation level may be defined, Chapter 1. Introduction to Radio Variability 5 where o is the root of the quadrature sum of the individual measurement uncertainties. Ideally, a number of data pairs over the interval At are taken, and the computed vari-ability measurements are averaged. Otherwise, one data pair must be assumed to be characteristic of the time scale At, which, strictly speaking, is only statistically true. If there are N flux density measurements, Fi, and uncertainties, o~i, taken at intervals Ati, with A t being characteristic, then we can define a Q value to the data set, quanti-fying both degree of variability and confidence level, that is more statistically valid. An observed goodness of fit, ~)^obs, of the data set to a default constant model is given by the expression N i=l T? T? I ^ r i r w (1.5) where Fw is an obvious extension of equation 1.3 to N measurements. The data set Q value is then the probability of a x 2 larger than xlbs occurring by chance if the constant model assumed is correct, and is given by an incomplete gamma function with v = N — 1 degrees of freedom. For convenience, the negative logarithm of the Q value is usually quoted, with a greater — logQ value corresponding to increased variability confidence. The — log Q cutoff for considering a source to be significantly variable is somewhat arbi-trary, but is typically 2 or 3. The Q value is dependent on number and uncertainties of the parameter measurements and statistically valid for a range of A t , determined by the Ati population. For brevity — logQ is defined as Q, and hereafter used interchangeably. Chapter 2 Radio Variability Mechanisms To design the V L A study, and later interpret the results, it is important to understand short term variability mechanisms to which the project is sensitive. The vast majority of GB6 sources is undoubtedly extragalactic, and the most likely mechanisms for short term variability include highly beamed A G N , or extragalactic sources made to appear variable by interstellar scintillation. By selecting only short term highly variable sources we hoped to increase the chance of detecting galactic objects, perhaps galactic jet sources or radio stars. High resolution images of a wide variety of radio sources, both galactic and extragalactic, can be found in reference [16]. 2.1 Active Galactic Nuclei Active galactic nuclei (AGN) are, as their name suggests, associated with the central region of distant galaxies, characterized by relatively high luminosities emanating from a tiny galactic volume. The primary feature of current models for these powerful objects is a supermassive black hole at the center of a galaxy, with the gravitational potential of the black hole being the main power source. Interstellar material is drawn towards the black hole and emits UV-rays, soft X-rays, and eventually hard X-rays as the plasma forms a rapidly rotating accretion disk around the black hole. The large scale motion of plasma induces powerful magnetic fields which facilitate the ejection of synchrotron emitting plasma, in highly collimated jets, at relativistic speeds, along the poles of the rotation axis. The high energy and relativistic physics involved make A G N of broad scientific 6 Chapter 2. Radio Variability Mechanisms 7 interest and detailed theoretical models of extragalactic beams and jets, as presented in [13], have been formulated. Since the A G N model is axisymmetric, the appearance, and current classification of these objects is dominated by orientation [17]. 2.1.1 Unification Schemes Attempts are currently being made to classify and understand A G N based on more appropriate physical characteristics instead of parameters dependent on aspect angle [17]. Previously, radio loud A G N , those with a radio to optical flux ratio greater than ten, were classified based on radio and optical luminosity, width of emission lines, radio spectral indices, and polarization level. It has now been accepted that most radio loud A G N belong to two main classes, based on Fanaroff-Riley luminosity levels and differences in appearance are due primarily to beam orientation with respect to the observer [17]. In particular, it is believed that F R II galaxies, steep spectrum radio quasars, and flat spectrum radio quasars constitute one morphological type while F R I galaxies and B L Lacertae objects form another. In this combined scheme, A G N may be interpreted as a continuum with radio galaxies having beam axes nearly perpendicular to the line of sight and blazars being viewed almost directly down the beam axes. Clearly there is merit in this unification scheme, however it is undoubtedly an oversimplification since some A G N characteristics can not be adequately incorporated. Furthermore, A G N classification is complicated by different levels of circumnuclear obscuration due to material near the galactic core and observed redshifts. 2.1.2 Relativistic Effects The rapid flux variations, high polarization and luminosity levels observed in some ra-dio loud A G N are believed to be due to relativistic beaming [17]. Special relativity Chapter 2. Radio Variability Mechanisms 8 \ Figure 2.1: V L A 20 centimeter image of F R II radio galaxy 3C219. The radio galaxy is at a red shift of z = 0.1745, shown here with a resolution of 1.4 arcseconds. Large radio lobes extending hundreds of kiloparsecs, with hot spots, are seen in this image, as well as a two-sided jet and a bright core. Adapted from [18] ) Chapter 2. Radio Variability Mechanisms 9 transformations of time and frequency from the rest to observers frame are given by A t ' A t = ^ - (2.1) v = 8v' (2.2) where the primed variable is in the rest frame of the jet, and the Doppler factor, 8, is 6 = [7(1-/? cost?)]-1 (2.3) with j3 the bulk velocity normalized by the speed of light, 6 the angle between the velocity vector and the line of sight, and 7 being the Lorentz factor 7 = (1-/?T1/2. (2.4) A direct result of equations 2.1 and 2.2 is a decrease in the variability time scale and a blue shift of the flux as seen in the observers frame. In extreme cases the transverse velocity of the relativistic motion may appear to be superluminal. A n in depth discussion of observations and theory of superluminal sources may be found in reference [14]. The relativistic transformation of angles implies forward beaming of an intrinsically isotropic radiator. The combined effect of relativistic beaming and the doppler frequency band compression is amplification of the intrinsic broad band rest flux density F = 84F' (2.5) and flux variation A t A t v ' Both equation 2.5 and 2.6 are strongly dependent on the Doppler factor (equation 2.3), plotted in figure 2.2 for various velocities and observation angles. This strong dependence of equation 2.6 means that A G N may appear to be significantly variable, in the core, on short time scales. Equation 2.5 can dramatically increase the core to extended emission Chapter 2. Radio Variability Mechanisms 10 flux ratio as well as enhancing the flux from the approaching jet while quenching the receding jet. Clearly some A G N may appear as either one-sided or with no extended structure at all. 2.2 Galactic Jet Sources In our galaxy there exists smaller scale counterparts of the active galactic nuclei. These recently discovered galactic relativistic jet sources exhibit a wide range of characteristics, as do their extragalactic analogs: from superluminal jet sources like GRS 1915+105 and G R O J1655-40, and relativistic jet sources SS433, GRS 1758-258, Cyg X-3 and 1E1740-2942, to the flat spectrum X-ray binaries: Cyg X - l , Cyg X-2, Sco X - l , and Cir X - l , also proposed as jet sources. Galactic jet sources are associated with binary systems containing a black hole, or neutron star, often with a transient hard X-ray and 7-ray signature. Surrounding the compact object is an accretion disk with characteristics temperatures of approximately 10 keV [3], and a pair of highly collimated, relativistic particle jets, extending light years from the central objects, emitting synchrotron radiation. The particle jet usually takes the form of episodic ejections of large clouds of plasma (plasmons). A schematic diagram of the relativistic jet source SS433 is shown in figure 2.3. GRS 1915+105, almost certainly a black hole [3], and discovered in 1992 with the G R A N A T satellite, exemplifies the physical behaviour of relativistic jet sources. Located towards the center of the galaxy, with galactic coordinates / = 45.4° and b = —0.3°, it is estimated to be approximately 12.5 ± 1.5 kpc away, and has been identified with an infrared counterpart, although no optical counterpart has yet been observed. GRS 1915+105 has been extensively monitored with the V L A at various frequencies, and studies have yielded parameter measurements for a kinematic model. Chapter 2. Radio Variability Mechanisms Figure 2.2: Doppler factor for different 8 and 9 Chapter 2. Radio Variability Mechanisms 12 Figure 2.3: Schematic representation of galactic relativistic jet source SS433. Adapted from [20]. Chapter 2. Radio Variability Mechanisms 13 Figure 2.4: Radio maps of microquasar GRS1915+105 imaged with the V L A at 3.5 centimeters (from [3]). Contours are 1, 2, 4, 8, 32, 64, 128, 256,and 512 times 0.2 mJy/beam for all epochs except for March 27 for which the contour unit is 0.6 mJy/beam. A pair of plasmons can be seen moving away from the stationary core, marked by a cross. Chapter 2. Radio Variability Mechanisms 14 -1 -0.5 0 Angular Displacement (arcsec) o CD S 1-5 (0 i M 1111111 M M 11111111111 M 111111111111 l_ GRS 1915+105 C CD CD O 1 h 0.5 Si _cC c < . • . • ' >'l I I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 10 20 30 40 50 60 70 80 Time Since Ejection (days) Figure 2.5: Angular displacement as a function of time after ejection, and 3.5 centimeter flux density as a function of angular displacement, for observed plasmons of microquasar GRS 1915+105. Top and bottom lines in both graphs are regression fits for approaching and receding jets respectively. Adapted from [3]. V L A images (figure 2.4) clearly show bright radio condensations, or plasmons, emerg-ing from the central compact object. The shown plasmons are believed to have been ejected on March 19, 1994 at 20+5 universal time. From the observed motion of 17.6+0.4 mas/day and 9.0 ± 0.1 mas/day, corresponding to 1.25c and 0.65c, for the approaching and receding jet respectively, true ejection velocity has been determined as 0.92c, with the jet axis at 70° to the line of sight [3]. This relativistic plasma velocity yields a doppler factor of S = 0.56 for the approaching jet (eqn 2.3). As the condensations move away from the core, they are observed to fade, but the approaching and receding flux ratio remains constant at 8 ± 1, consistent with relativistic beaming [3]. Chapter 2. Radio Variability Mechanisms 15 2.3 Radio Stars A l l radio stars are intrinsically variable, typically on a time scale of hours, and may be loosely classified as a flare star, radio nova, pulsar, X-ray star, or belonging to a close binary system. Although pulsars can be extremely variable with clocklike periodicity, the pulse time scales are usually less than a second and therefore too short for consideration here. X-ray stars, correlated with galactic jet sources, are discussed in section 2.2. Stellar flares are associated with plasma being ejected from active starspot regions. These flares usually produce coincident optical and radio outbursts, but to be detectable, the radio emissions must be orders of magnitude greater than those associated with solar flaring. For this reason, flare stars commonly belong to binary systems, where the companion may act as a catalyst for more frequent and powerful flaring activity. The mechanism of the radio emission is not well understood, but typically the radiation occurs at meter wavelengths, varying on a time scale of hours, with a non-thermal spectrum, or at shorter centimeter wavelengths, with slightly longer time scales, and being partially circularly polarized [12a]. Radio novae, as their optical counterparts, are quasi-periodic explosions on the surface of a star which rapidly accelerates an ionized plasma Shockwave. This exploding shell of gas typically produces thermal radiation with a changing spectral index. Prototypical examples of a radio novae include Nova Delphini and Nova Serpentis [12a]. It is worthy of note that although most radio stars have angular diameters a lot less than an arcsecond, this is not necessarily the case for radio novae. Radio stars belong predominantly to binary systems [15], since the interaction of a stellar pair can induce both flaring and nova activity. A particularly interesting class of binary systems, known as a symbiotic pair, consist of a red giant and a small companion, such as a white dwarf, in proximity to each other. The gravitational interaction of the pair Chapter 2. Radio Variability Mechanisms 16 may cause mass transfer from the giant. This spillover of gas results in the accretion of plasma on the surface of the compact companion and the formation of complex shockwave patterns. The emitted radio radiation is often thermal, with extreme variability. The radio emission may be quasi-periodic, and may increase quiescent flux density by an order of magnitude on a time scale of hours. 2.4 Interstellar Scintillation A n extrinsic mechanism for flux density variations in radio sources [6] is interstellar scin-tillation (ISS). Intrinsic mechanisms of variability in compact sources require extreme brightness temperatures or doppler factors. ISS is a result of both large and small scale irregularities or turbulence in the interstellar plasma, and effects all extragalactic sources at some level. Two phenomenological types of ISS occur: refractive (RISS) and de-fractive (DISS); however for typical compact extragalactic radio sources at centimeter wavelengths, RISS predominates [6]. Except in a strong scintillation regime, RISS is well modeled by the Born approximation of scattering theory. Two important parameters characterizing RISS are scintillation index (m), the mean normalized rms flux amplitude, and a scattering time scale (r), both of which are strong functions of source angular diameter (0). Significant RISS occurs only if the source diameter is of the order, or smaller than the scattering diameter (9^). Apparent source position shifts, on the order of the scattering diameter, may be a manifestation of RISS. The effect of RISS can be simply modeled [6] by an instantaneous phase shift, equal to the extended medium path length, occurring at a distance, L , from the observer. The extended medium consists primarily of two components, a wide galactic disk, and an enhancement galactic plane component. The galactic plane component varies spatially with galactic latitude and with proximity to the galactic center. For absolute galactic Chapter 2. Radio Variability Mechanisms 17 latitudes greater than five degrees, this component can be ignored. For an extragalactic point source, at absolute galactic latitude b, the scintillation index and time scale can be approximated by: • ) rriR ~ 0.5 rR(days) « ^ (2.7) where: L(pc) w 500 esc b 0^8A 2 ( c sc 6 ) 1 / 2 . Extended extragalactic source RISS is modeled by: Qds rriE ~ rrifi (8l + 02)1/2 r g(days) * L ^ + * ? ' * ( 2 . 8 ) with all angles measured in milliarcseconds, A in meters, and v, the velocity of the observer relative to the extended medium, in kilometers per second. The scintillation index and time scale are plotted in figure 2.6 for characteristic parameter values. The amplitude of flux variation increases with wavelength, but for most flat-spectrum, compact source models, the effective source diameter also increases with wavelength, and the scintillation index will eventually flatten out. As extended source diameters increase, spatially smoothed scintillation patterns yield smaller indices. The scintillation time scale for small wavelengths is effectively constant, but asymp-totically approach the point source limit at longer wavelengths, as source diameters in-crease. In general, RISS is a more successful explanation of small amplitude, short time scale variations, as high amplitude, long time scale variations are more likely intrinsic Chapter 2. Radio Variability Mechanisms 18 Wavelength (cm) Wavelength (cm) Figure 2.6: Scintillation index and time scale plotted versus wavelength and source di-ameter. Characteristic values of galactic latitude (|6| = 45°) and velocity (v = 50 km/s), representing the earths orbital motion and peculiar velocity of the sun. Source diameters are 50,10,2,0.5,0.1,and 0.02 mas from right to left and from top to bottom on index and time scale plot respectively. Chapter 2. Radio Variability Mechanisms 19 1.7 1.6 1.5 » 1.4 c 1.3 1.2 -i 1 1 r A \ / \ "t 1 1 1 1 1 1 1 r 0917+624 / * / \ t * / \ f i i i i i i i i i i i i i 6 cm i i I i i i I 3 4 5 Julian Date - 2447522 Figure 2.7: Flux density of source 0917+624 at 6 centimeter wavelength as a function of observation date. RISS is well established as the cause of the intensity variations. Modified from [6]. to the source [6]. In any compact extragalactic radio source, however, RISS is always a component and must be considered as an explanation for observed flux density variations. The intra-day radio variable 0917+624 has been studied over the last eight years at multiple wavelengths. This source exhibits rapid flux variations on a time scale of hours, with significant amplitudes (see figure 2.7). These flux variations are wavelength corre-lated, with no time delay [7], contrary to the wavelength dependent time delay predicted by intrinsic variation models. 0917+624 also exhibits random position variations on time scales comparable to the flux variations at centimeter wavelengths [7]. RISS is believed to be the mechanism of a variety of radio source variability [6], including the long term variations seen in pulsars. At centimeter wavelengths, RISS is the likely cause of flat-spectrum flux variations of a few percent [6]. C h a p t e r 3 G B 6 L o n g T e r m V a r i a b i l i t y As an aside to the author's main research, aspects of population statistics for a recently generated GB6, greater than 2.5 sigma confidence, long term variability list, were stud-ied. Here, long term variability is defined by a time scale of approximately a year. The variability confidence cutoff level, for scientific usefulness, is somewhat arbitrary, but achieving large number statistics must be balanced with introducing an increasing frac-tion of spurious variables. The long term variability list used is believed to represent a reasonable confidence limit, with the implicit understanding that inclusion of sources with confidence level of 2.5 sigma or greater implies that the variability of approximately 13.5% of the 6918 sources is the statistical artifact of parameter noise, with the proba-bility of false variability increasing for smaller confidence levels. 3.1 G a l a c t i c P r o j e c t i o n a n d V a r i a b i l i t y I n d e x D e p e n d e n c e The long term variable source positions have been plotted, in figure 3.1, in an Aitoff galactic projection, with GB6 survey boundaries as shown. With the exception of a noticeable cluster of sources, towards the local Cygnus arm in the galactic plane, the spatial distribution appears to be both isotropic and homogeneous, consistent with the extragalactic object hypothesis for the vast majority of GB6 sources. The galactic latitude dependence of the observed long term variability index is graphed, in figure 3.2, along with a linear regression fit. The overall trend is a decrease in variability index at smaller absolute galactic latitudes, contrary to expected interstellar scintillation 20 Chapter 3. GB6 Long Term Variability 21 GALACTIC PROJECTION + 90° -90° Figure 3.1: Aitoff galactic coordinate projection for sources (6918) on > 2.5 sigma con-fidence GB6 long term variability list studied. GB6 survey boundaries are as shown. Chapter 3. GB6 Long Term Variability 22 £ 0.4 n I I i I I I I i 11 i i i i i 1 1 i i | i 1 1 i i i i i i | 1 1 i 11 1 1 1 i | i i 11 11 i i i | I I i i i i 1 1 1 | i i i i i 1 1 i 11 1 1 1 1 i i I I 11 i i i i 11 1 1 i. ' i ' 111111111111111111 i 11111 L i 1111 i 111111 • 10 20 30 40 50 i - i - . i — t 60 70 80 90 Absolute Galactic Latitude (Degrees) Figure 3.2: Variability index as a function of absolute galactic latitude, for sources on the > 2.5 sigma confidence GB6 long term variable list. Linear regression is included. (ISS) effects, most likely the result of a GB6 selection effect due to stricter detection thresholds for low galactic latitude sources. The exact dependence of ISS on galactic latitude is a complicated function, dependent primarily on interstellar material column densities, and observed variabilities are further complicated by limited sampling. The ripple, or oscillation apparent in figure 3.2, if interpreted as due to ISS, suggests approx-imate characteristic object angular sizes of 0.5 milliarcseconds, varying on time scales of several days, based on a scintillation index on the order of 10~2, for GB6 observations. 3.2 Spectral Index Fraction Density To extract spectral index information the N R A O V L A Sky Survey (NVSS) database was searched for positional matches, for all the GB6 long term variables and all sources in the GB6 catalog, within thirty arcseconds of the GB6 positions. The NVSS database, discussed in section 4.2.1, contains 20 centimeter flux density measurements, and matches were found for approximately 40% of the long term variables, with 2% being unmatched, and the remaining 58% lying in regions not currently covered by NVSS. The computed spectral indices (defined here by F oc A Q ) were binned and the discrete approximation to Chapter 3. GB6 Long Term Variability 23 1.2 Spectral Index Figure 3.3: Fraction density distribution as a function of spectral index for GB6 long term variables (dotted line), and entire GB6 catalog (solid line), matched with NVSS database. Chapter 3. GB6 Long Term Variability 24 the fraction density, f(a), given by f{Oi) NAa (3-1) where rij is the number of sources in the i bin of width Act, and a* being the central bin value, is plotted in figure 3.3 for NVSS matches of both the long term variables and the entire GB6 catalog. The total number of sources in each sample, N, normalizes the Both fraction density distributions have a well defined steep spectrum peak near 0.8, consistent with that expected for an extragalactic population of normal radio-loud galaxies [12b]. However, the fraction density distribution of the long term variables has a distinct flat spectrum component which is significantly more pronounced than in the smoother distribution for the entire catalog. To elucidate the origin of the long term variable flat spectrum shoulder, the centroid of the fraction density distribution is graphed in figure 3.4, as a function of GB6 flux, Va sigma confidence level (eqn. 1.4), and variability index, along with linear regression fits. Based on the dependence of the spectral index centroid in the graphs it is concluded that these flat spectrum objects have relatively high flux densities. Variability confidence levels are a function of flux density, and therefore confidence levels associated with these objects are also high. Since the long term variability list is confidence level limited, the sample of sources is biased towards these flat spectrum objects. There is no clear trend in spectral index as a function of variability index, with only slightly lower spectral indices for low variability index objects, that very likely the result of GB6 variability selection effects. The relatively high flux densities of these flat spectrum objects implies either relative proximity of these extragalactic sources, or more likely, that they are intrinsically brighter, perhaps due to extreme relativistic Doppler enhancement of the flux density. One may tentatively hypothesize that these objects are blazars, with only function so that the definite integral J f ^ f(a) da is unity. Chapter 3. GB6 Long Term Variability 25 the extremely beamed flat spectrum cores visible. It must be cautioned in the interpretation of the spectral index fraction density that there has been no attempt to remove unknown cosmological redshift, or forward beaming blueshift effects. As well, it is expected that there is a slight spectral index distribution skewing due to the fact that 6 centimeter flux density measurements were taken on a single dish, whereas the 20 centimeter data were taken on a spatially filtering interferometer, which is less sensitive to extended emission. 3.3 V a r i a b i l i t y F r a c t i o n D e n s i t y A variability fraction density can also be defined for either a sigma confidence level, Va, or a variability index, V, similar to the definition of spectral index fraction density given in equation 3.1. The fraction density of GB6 sources, as a function of sigma confidence level (eqn. 1.4), for Va > 2.5, can be determined directly from the long term variability list. The computed GB6 fraction density of the Va is plotted in figure 3.5 with a linear regression fit. For confidence levels between 7.5 and 2.5, the linear fit is reasonable and can be believably extended to lower sigma values, but for sigma values greater 7.5 the computed GB6 fraction density deviates from the linear fit and flattens out. The sigma confidence level is survey dependent, being directly related to characteristic flux density uncertainties, and the number of sources at a particular confidence level also depends on gaussian statistic probabilities. However the Va fraction density also reflects the intrinsic population variability. From graph 3.5 one can determine the number of GB6 sources having a particular long term variability confidence level. As mentioned in the previous section, the GB6 survey sensitivity in detecting vari-ability diminishes for lower variability indices. The GB6 selection factor, shown in figure 3.6, is a function of variability index and the sigma confidence level cutoff. The GB6 Chapter 3. GB6 Long Term Variability 26 0.8 1 1 > 1 1 1 11 11 i 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 i 1 1 11 1 i 1 1 1 11 11 1 11 M 1111 i 11 i 1 1 1 1 -0.4 0.8 x •S 0.6 c i 0 - 4 1 0.2 M 0 0.8 x •g 0.6 «u 0.4 I 0.2 i i i I i i i i i i i i i I i i I i i i i i i i i i I i i i I i i i i I II 100 200 300 400 GB6 Flux Density (mJy) 500 600 700 n — i 1 — i 1 1 1 1 1 1 r T 1 1 1 r n 1 r - 3 f % i T i i T i L . -J I I L. I I I I I I I I I I I I I ,, | I t I I I I I 4 5 6 Sigma Confidence Level " i — i — i — i — i — n — i — i — I — i i i i i — i i i - | — i — i — i — i | i i — n — T T — n — i - ] - ! — i — i — r - p i—i—i—i—I—i—i—i—r IjJ_ Jj_i_|__L i J i i i i i i i ' i i i i i ' i i i i i J_J i I_I L_i i i i I i i i i I i i i i I 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Variability Index Figure 3.4: Spectral index centroid plotted versus GB6 flux density, sigma confidence level, and variability index, with associated linear regression fits. Chapter 3. GB6 Long Term Variability 27 Cl v -1 C o o _o (0 ^ CD O ->3 ao o ~i—i—i—i—i—i—r H — i — i — | — i — i — i — i — i — i — i — i — i — I I i — i — r i—I—i—i—i—i—I—i—i—i—i—I—i—i—i—r " t o . I 1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ' ~ ' - ' L 0 3 4 5 6 Sigma Confidence Level 10 Figure 3.5: Logarithm of GB6 fraction density as a function of sigma confidence level, with linear regression fit. selection factor may be interpreted as the fraction of GB6 sources that could in principle have been detected at a variability index, V, at a > No confidence level. This was computed directly from the entire GB6 list of sources. The selection factor plotted in figure 3.6 is for a 2.5 sigma confidence level cutoff, but as sigma cutoff levels decrease, the selection factor approaches unity for lower variability indices. The directly determined GB6 fraction density, as a function of variability index, V (eqn. 1.1), can be corrected for the GB6 variability index selection effect, by normalizing with the GB6 selection factor. The resultant corrected GB6 fraction density of variability index data (figure 3.7) becomes significantly uncertain at lower variability indices since, even at the 2.5 sigma confidence level cutoff, the GB6 selection factor approaches zero. A more accurate estimate of the GB6 fraction density at low variability indices was obtained by fitting a polynomial to the integrated cumulative GB6 fraction of sources with a variability index greater than a particular variability index. Since all GB6 sources Chapter 3. GB6 Long Term Variability 28 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Variability Index Figure 3.6: GB6 variability selection factor as a function of variability index for a 2.5 sigma confidence level cutoff. must have a V > 0, the boundary condition that the cumulative GB6 fraction be unity at V = 0 is applied to the polynomial fit. A plot of the cumulative GB6 fraction data, with derived low variability index fit is given in figure 3.7 and the estimated low variability GB6 fraction density is included in figure 3.7. The determined GB6 fraction density versus variability index, with the exception of flux density detection thresholds, is reasonably survey independent, and places con-straints on any models of extragalactic radio source variability, in particular the unified beam model. Chapter 3. GB6 Long Term Variability 29 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 Variability Index u Variability Index Figure 3.7: Logarithm plot of directly computed, and corrected model of, G B 6 variability fraction density and cumulative G B 6 variability fraction as a function of variability index. Chapter 4 G B 6 Short T e r m Variabil ity The selection process for the radio sources suitable for a short term variability V L A study began with a list of 499 GB6 sources for which daily flux density measurements had been previously extracted (short term variability list [STVL]), from the raw GB6 scan data, for another variability study [2]. Originally, the referenced researcher intended for the above list to include sources with long term variability at the 5 sigma level of confidence, or greater. Due to small flux density corrections, this is not strictly true, with the list now containing a number of sources down to the 4.5 sigma level, and can no longer be considered complete for the 5 sigma level. 4.1 Q Value Statistics and Selection The negative logarithm of the Q value, discussed in section 1.3, and here after referred to as Q, was computed from the daily flux density measurements. A galactic Aitoff projection plot of the positions for all sources on the short term variability list is shown in figure 4.1, and sources with a Q value greater than either 2 or 3, during both 1986 and 1987 epochs are highlighted. From the galactic projection there is no evidence for galactic concentration in the short term variability list as a whole, and only slight evidence for sources exhibiting strong short term variability. The normalized density p(Q), defined as where p(Q) is the number of sources per unit Q at a particular Q value, and pQ is the expected value of p(Q) assuming a uniform number distribution, is plotted in figure 4.2 for both epochs. The overall trend 30 Chapter 4. GB6 Short Term Variability 31 GALACTIC PROJECTION +90° -90" • Short Term Variability Sources A Sources with —log Q > 2 • Sources with —log Q > 3 Figure 4.1: Galactic coordinate Aitoff projection of sources on short term variability list. Sources with either — logQ epoch values greater than 2 or 3 are highlighted. Chapter 4. GB6 Short Term Variability 32 is the same for both the 1986 and 1987 epochs, and most sources are not significantly variable (Q > 2) on short time scales, at the achieved survey confidence levels. Two scatter plots are included in figure 4.3, for Q at both epochs versus Va, the long term variability confidence level, and for 1986 Q values versus 1987 values. There is no obvious connection between Q and Va values, which is reasonable considering the large difference in time scales involved and statistical sampling effects. Since the long term and short term variability information is effectively uncoupled, the original restriction of the short term variability list to long term variables at approximately the 5 sigma level, or higher, is of little consequence, and the short term variability list can be considered a pseudo-random sample of GB6 short term variability. Unfortunately, there is also no obvious correlation between 1986 and 1987 Q values, suggesting that a fraction of the sources is only occasionally variable on short term time scales. However even consistently periodic short term variables may generate different Q values due to sampling effects. To maximize short term variability, and the probability of observing variability during the V L A short term variability study, the sources in the short term variability list (STVL) were sorted by the multiplied 1986 and 1987 epoch Q values. The sorting function, used to prioritize the variables for further selection, is overlaid on the Q scatter plot in figure 4.3, for values of 1, 4, 9, and 16. 4.2 External Database Search To gain further insight into the sources on the short term variability list, and to select sources without known identifications for further study, various databases were searched, with the results summarized in tables, only for the 178 sources (short term variables [STV]) with either Q epoch value > 2, included in appendix A . Chapter 4. GB6 Short Term Variability 33 C <D Q TJ <D N £ o -l 1 r n 1 r ~i 1 r Po = 48.5 x 8 6 = 1.31 x 8 7 = 1.36 1986 Epoch 1987 Epoch j i i _ ir ->i----t--f-_i-_-^#. i ± i " — 4 6 - log 1 0 Q 10 Figure 4.2: Normalized density of sources as a function of short term variability (— logQ) for both 1986 and 1987 epochs. Chapter 4. GB6 Short Term Variability 34 Of O 1 1 I 1 \ | r V _ 1 1 1 ' 1 r--I - I \ \ I. • \ \ X i i \ ^ V 0 2 4 - l Q g l O Q 8 6 Figure 4.3: Scatter plot of 1986 versus 1987 epoch short term variability (Q = — logQ), with the sorting function Q86 x Q%7 overlayed for values of 1, 4, 9, and 16 at left. Scatter plot of short term variability versus long term variability confidence level Va at right. 4.2.1 N R A O V L A Sky Survey To get high resolution images of any of the short term variables, it is desirable to have more precise pointing positions than those determined by the GB6 survey, with a charac-teristic uncertainty of 13". The N R A O V L A Sky Survey (NVSS) is a project undertaken by N R A O to image the sky, at a resolution of 45", between declinations of -40 and +90 degrees at 20 centimeters (1.4 Ghz). Products of the NVSS include intensity and polariza-tion maps as well as a catalog of discrete sources with accurate positions, with minimum uncertainty of 0.3" for strong sources, and flux density measurements, for all sources above the 2.5 mJy detection threshold. Currently, the NVSS catalog source information is available for approximately 50% of the overlap regions between the NVSS and GB6 surveys. The NVSS catalog was searched in January 1997 for positional matches within 30" of the GB6 positions, to allow primarily for GB6 positional uncertainties. According Chapter 4. GB6 Short Term Variability 35 to NVSS documentation, there is a 1 % probability of a NVSS source occurring randomly at a distance of 30" from any arbitrary position. NVSS matches were found for 93 of the short term variables (STV), within the 30" boundary. The best positions for all short term variables, with uncertainty in arcseconds are listed in appendix A . l . The positional catalog of origin, either NVSS or GB6, is also given along with positions in galactic coordinates. In appendix A.2, 1986 and 1987 epoch flux density measurements, F 8 6 and F 8 7 , as well as the combined flux density, F 6 , from the GB6 catalog, and the NVSS flux density, F2o, are listed, along with the spectral indices derived from the 6 and 20 centimeter flux data. The GB6 short term variability 1986 and 1987 epoch Q values and the GB6 long term variability confidence level is also included in the table. 4.2.2 SIMBAD and NED Databases Two comprehensive astrophysical databases, compiled from numerous catalogs at a wide range of wavelengths, were searched to determine which of the short term variables (STV) are previously identified sources. SIMBAD1 is a database, primarily of galactic objects, with access provided by the Canadian Astronomy Data Center ( C A D C 2 ) . SIMBAD was searched for matches within 5" of NVSS positions and 30" of GB6 positions to allow for GB6 and NVSS position uncertainties as well as SIMBAD source position uncertainties. Of the short term variables, 42 matches were found, with the summarized results given in appendix A.3. The table includes the SIMBAD object classification, SIMBAD position 1 S I M B A D is maintained by CDS (Centre de Donnees astronomiques de Strasbourg) at the Strasbourg Astronomical Observatory, an institute of Universite Louis Pasteur in Strasbourg, France. S I M B A D documentation is found at http://cdsweb.u-strasbg.fr/Simbad.html . 2 T h e C A D C is operated by the Dominion Astrophysical Observatory for the National Research Council of Canada's Herzberg Institute of Astrophysics. The C A D C homepage is accessed at http://cadcwww.dao.nrc.ca/. Chapter 4. GB6 Short Term Variability 36 and angular distance between G B 6 / N V S S and SIMBAD positions in arcseconds. Eigh-teen of the matches are identified as having appeared on a previous radio survey, with no other classification, and therefore does not disqualify a source from further study. The remaining classifications are dominated by 19 A G N , including radio galaxies, B L Lacer-tae objects, and a notable 11 QSOs, suggesting a Q dependent bias for highly relativistic beamed objects. The N A S A / I P A C Extragalactic Database (NED3) was searched, in a similar manner, for short term variable identifications. The NED includes known source names and aliases, photometry and redshift data when available, publication references, and multiple classifications based primarily on wavelengths at which the object has been detected. The NED search results are summarized in appendix A.4, for the 115 short term variables matched. Most of the matches correspond to previous detection by radio wavelength surveys, excluding the GB6 and NVSS surveys, with the number, if > 1, of independent detections, listed in the radio column of the table. The most common classifications, other than as a radio source, is as a QSO (21), an X-ray source (11), or a galaxy (7), and corresponding sources are identified in the table. Any other identification is given in the last column of the table, including most notably 7-ray sources (GammaS), infrared sources (IrS), visual sources (VisS), and either absorption (AbLS) or emission (EmLS) line sources. Again, QSOs dominate galaxies as specific classifications, with all but one of the X-ray detections associated with QSOs. 4.2.3 APS Optical Counterparts Sources with positional accuracy on the order of an arcsecond, as obtained by NVSS, can be reliably correlated with optical counterparts. The Digitized Sky Survey (DSS) is a 3 The N E D is operated by the Jet Propulsion Laboratory, California Institute of Technology, un-der contract with the National Aeronautics and Space Administration. The N E D is accessed via http://nedwww.ipac.caltech.edu/. Chapter 4. GB6 Short Term Variability 37 project by the Space Telescope Science Institute (STScI) to digitize the Palomar Obser-vatory Sky Survey (POSS I) blue (0) and red (E) plates, and make the images available via the N A S A / H E A S A R C virtual internet observatory "SkyView 4". The University of Minnesota, in association with N A S A and NSF, have undertaken the task of using an Automated Plate Scanner (APS5) to identify every source on the DSS images as either a star or a galaxy, and to derive source positions, magnitudes, and colour. Object classi-fication is determined by a neural network algorithm, by computing probabilities based on source intensity profile, and it is implicitly assumed, for convenience, that objects can only be stars or galaxies. Currently, the APS research group claims a 90% classification success rate. Photometry for stars is calculated using a calibrated magnitude-diameter relationship, and photometry for galaxies is based on derived and calibrated density to in-tensity transformations. With precise plate scanning measurements and plate distortion corrections, the calibrated position total errors are approximately 0.6". When completed, the APS catalog should include millions of sources, with absolute galactic latitude > 20 degrees. Currently only a fraction of the project data is available. In January 1997, all short term variability sources (STVL) with NVSS positions were checked, within 3", in the APS catalog. The APS correlation results for the short term variables (STV) are listed in appendix A.5. The table includes APS classification, APS position, angular distance between APS and NVSS position in arcseconds, and the APS derived blue (O) magnitude and colour (O-E). Among the short term variables (STV) there were 16 APS matches, with 12 being identified as stars and 4 as galaxies. It is clear from the NED and SIMBAD identifications that APS will characteristically misclassify 4 SkyView was developed and is maintained by NASA under the auspices of the High Energy As-trophysics Science Archive Research Center (HEASARC) at the GSFC Laboratory for High Energy Astrophysics. The SkyView homepage URL is http://skview.gsfc.nasa.gov/skyview.html. 5 The A P S Catalog of the POSS I is supported by the National Science Foundation, the National Aeronautics and Space Administration, and the University of Minnesota. The A P S databases can be accessed at http://isis.spa.umn.edu/. Chapter 4. GB6 Short Term Variability 38 O Magnitude Colour (O-E) Figure 4.4: Normalized density of APS matched short term variability sources as a function of magnitude (left) and colour (right). an A G N as a star, since a third of the short term variables (STV) identified by APS as stars is identified by NED as a QSO or by SIMBAD as some type of A G N . For completeness, the normalized density of magnitude and colour of the short term variability (STVL) sources is shown in figure 4.4. Although the distributions are intrigu-ing, it must be cautioned that any direct interpretation is difficult since neither galactic extinction, interstellar reddening, nor APS/DSS selection effects have been corrected, and small number statistics may further distort the underlying distribution. 4 . 3 S e l e c t e d V a r i a b l e S o u r c e s f o r V L A S t u d y From the list of short term variables (STV), prioritized by multiplied epoch Q values, and with all previously identified sources removed, the top 24 sources were chosen for Very Large Array (VLA) imaging. The number of sources chosen for study was based on initial expectations for V L A time allotted and estimates of observation time required Chapter 4. GB6 Short Term Variability 39 per source to achieve sufficient sensitivity at two wavelengths. A separate summary of source positions in J2000 coordinates, with uncertainty in arcseconds, positional catalog of origin, and position in galactic coordinates is given in table 4.1. A plot of position in an AitofT galactic projection, for the 24 sources selected for V L A study, are highlighted in figure 4.5 along with galactic positions for all sources on the parent short term variability list (STVL). It is worthy of note that, even though galactic position was not a selection criterion, of the 24 sources, 11 lie within 15 degrees of the galactic plane, which is at least encouraging since it is hoped that some of the studied objects are galactic. Flux density measurements from the 1986 epoch, 1987 epoch, and combined GB6 data, the NVSS flux measurements and derived spectral indices, a, as well as the 1986 epoch and 1987 epoch Q values, and long term variability sigma confidence level are summarized in table 4.2. The GB6 flux density measurements range from a relatively weak 25 mJy to a strong 626 mJy, averaging about 170 mJy, and of the spectral indices derived for NVSS matches, the majority is flat as expected. NVSS flux density measurements, and in particular, positional information, were available for only half of the sources just prior to the V L A observations. A l l the sources were also checked in a catalog of sources detected by the Faint Images of the Radio Sky at Twenty-cm (FIRST 6 ) survey. The available catalog of the FIRST survey, with a detection threshold of 1 mJy, a resolution of 5", and with positional accuracy < 0.5", is currently sparse, and only one source, J l 106+282, which already is NVSS matched, was found. The FIRST measured flux density, of 215 mJy, is consistent, especially considering GB6 levels of variability, with the NVSS measurement. By definition of the selection process, none of the 24 sources has specific previous identifications; however a number have appeared in other radio surveys. The SIMBAD 6The FIRST homepage is available at http://sundog.stsci.edu/ . Chapter 4. GB6 Short Term Variability 40 GALACTIC PROJECTION + 90° 180° 180° -90° • Short Term Variabi l i ty Sources o Sources Observed with VLA Figure 4.5: Galactic coordinate Aitoff projection of short term variables selected for V L A study along with distribution of all short term variability sources. GB6 survey boundaries are as shown. Chapter 4. GB6 Short Term Variability 41 Table 4.1: Selected Source Position Information N A M E J2000 Position . ± Catalog Galactic J0048+684 0:48:35.4 +68:26:29 9 GB6 5.6 122.7 J0049+343 0:49:45.7 +34:22:30 12 GB6 -28.5 122.5 J0251+562 2:51:54.53 +56:16:19.1 0.4 NVSS -2.8 139.1 J0259+516 2:59:38.23 +51:38:14.5 0.4 NVSS -6.3 142.3 J0502+388 5: 2:32.46 +38:49:54.9 0.5 NVSS -1.8 166.8 J0502+346 5: 2:29.88 +34:36:34.7 0.4 NVSS -4.4 170.2 J0532+562 5:32:59.47 +56:12:24.8 0.4 NVSS 12.3 155.4 J0611+723 6:11: 9.20 +72:18:16.3 0.5 NVSS 22.8 141.9 J0856+717 8:56:54.60 +71:46:24.9 0.4 NVSS 35.3 142.0 J0903+636 9: 3:37.94 +63:38:11.8 0.4 NVSS 38.6 151.4 J1106+282 11: 6: 7.22 +28:12:47.3 0.4 NVSS 66.7 204.1 J1307+064 13: 7: 4.0 + 6:27:54 13 GB6 69.0 313.8 J1603+110 16: 3:42.7 +11: 5:46 11 GB6 42.2 23.0 J1630+741 16:30:26.52 +74: 9:33.1 0.4 NVSS 35.4 107.1 J1700+685 17: 0: 9.24 +68:30: 6.5 0.4 NVSS 35.2 99.6 J1814+228 18:14: 1.5 +22:49: 3 24 GB6 18.1 49.9 J1924+286 19:24:14.7 +28:38: 0 12 GB6 6.1 62.0 J1956+635 19:56:25.8 +63:32:42 8 GB6 17.3 96.3 J2055+613 20:55:39.4 +61:22: 1 8 GB6 10.4 98.3 J2115+367 21:15:39.5 +36:45:56 11 GB6 -8.4 82.0 J2145+187 21:45:14.35 +18:45:19.8 0.4 NVSS -25.7 73.2 J2152+653 21:52:28.0 +65:20:35 9 GB6 8.7 105.7 J2202+292 22: 2: 5.3 +29:14:53 12 GB6 -20.6 84.1 J2208+615 22: 8:10.2 +61:32:55 11 GB6 4.6 104.7 radio position and angular separation, in arcseconds, from G B 6 / N V S S position is in-cluded in table 4.3 along with NED radio matches, with number of surveys (if > 1) and survey names listed. The most common radio survey catalog (WB92) is based on the Westerbork Northern Sky Survey (WENSS) at 92 centimeters. Other catalogs listed in-clude the 7C and 8C, part of a series of Cambridge University surveys, at 151 MHz and 38 MHz respectively, taken with the Mullard Radio Astronomy Observatory (MRAO). A l l radio surveys listed in table 4.3, compared to V L A capabilities, are low resolution and therefore offer no significant insight into possible sub-arcsecond structural variation of our selected sources. Since many of our selected sources have appeared in other surveys it is not unexpected that 13 have also been previously observed with the V L A in A, B, or hybrid configuration (table 4.3). However, according to V L A archive records, all of the previous observation programs are inconsistent with our multi-epoch observing Chapter 4. GB6 Short Term Variability 42 Table 4.2: Selected Source Flux Related Information N A M E F86 FS7. Fe F20 -logQse -logQs7 v„ J0048+684 49 ± 4 102 ± 5 81 ± 8 5.9 3.3 7.5 J0049+343 87 ± 6 141 ± 8 111 ± 10 5.9 1.6 5.4 J0251+562 352 ± 13 252 ± 10 310 ± 27 196 ± 6 -0.4 4.2 2.0 6.1 J0259+516 119 ± 6 61 ± 5 96 ± 9 89 ± 3 -0.1 1.2 11.7 7.1 J0502+388 172 ± 9 289 ± 13 239 ± 21 60 ± 2 -1.1 2.5 8.9 7.5 J0502+346 70 ± 6 114 ± 7 106 ± 10 178 ± 6 0.4 3.3 6.8 4.8 J0532+562 89 ± 5 130 ± 6 113 ± 10 111 ± 4 0.0 7.4 2.5 5.0 J0611+723 44 ± 4 116 ± 6 87 ± 8 60 ± 2 -0.3 6.3 3.3 10.1 J0856+717 144 ± 6 208 ± 7 174 ± 16 64 ± 2 -0.8 2.8 4.6 7.0 J0903+636 17 ± 5 33 ± 5 25 ± 4 50 ± 2 0.6 6.2 7.1 2.3 J1106+282 537 ± 24 274 ± 13 369 ± 33 225 ± 7 -0.4 6.0 1.5 9.6 J1307+064 151 ± 10 263 ± 14 146 ± 14 11.5 0.9 6.5 J1603+110 363 ± 18 831 ± 39 626 ± 55 0.6 16.8 10.9 J1630+741 86 ± 5 139 ± 6 116 ± 10 300 ± 9 0.8 5.7 2.6 6.8 J1700+685 341 ± 11 435 ± 13 380 ± 34 351 ± 12 -0.1 4.7 1.5 5.6 J1814+228 18 ± 7 40 ± 7 29 ± 5 7.0 6.0 2.2 J1924+286 140 ± 8 47 ± 5 92 ± 9 2.8 4.5 9.5 J1956+635 364 ± 12 143 ± 6 136 ± 12 22.2 1.8 16.1 J2055+613 307 ± 11 414 ± 14 385 ± 34 3.7 4.3 5.9 J2115+367 71 ± 6 136 ± 8 110 ± 10 1.6 13.4 6.8 J2145+187 45 ± . 6 88 ± 7 71 ± 7 79 ± 2 0.1 2.6 2.2 4.8 J2152+653 76 ± 5. 111 ± 6 92 ± 9 8.5 1.2 4.8 J2202+292 71 ± 6 116 ± 7 97 ± 9 3.0 4.6 4.8 J2208+615 47 ± 4 92 ± 5 67 ± 7 3.5 ' 5.7 6.4 strategy, typically consisting of one single-epoch, single-frequency snapshot. Usually, for even higher resolution V L B A or V L B I imaging, V L A imaging is a precursor, and the general lack of attention these sources have been afforded ensure that we avoid duplicating previous structural variability research. The GB6 short term flux density measurements for the 24 selected sources are plotted in figures 4.6 to 4.11 for both 1986 and 1987 epochs, with the first measurement in each epoch defined as occurring on day one. By selection criteria, all sources exhibit significant short term variability, on time scales from a day to a month, in at least one epoch, preferentially in both, and all sources exhibit long term variability, on a year time scale, by default because of sample list origin. A short term variation amplitude may be defined as the flux density standard deviation, normalized by the average flux density. The variation amplitudes for the selected sources, averaged over both epochs, Chapter 4. GB6 Short Term Variability 4 3 Table 4 . 3 : Selected Source Database Information N A M E SIMBAD N E D V L A Class Position (J2000) Distance (") Radio Survey (A/B) J0048+684 • J0049+343 • WB92 • J0251+562 • J0259+516 J0502+388 Radio 5: 2:32.45 +38:49:52.5 2.40 • B3 J0502+346 • WB92 J0532+562 • J0611+723 • J0856+717 • WB92 • J0903+636 • 8C J1106+282 • WB92 • J1307+064 • WB92 • J1603+110 • WB92 J1630+741 Radio 16:30:25.83 +74: 9:33.5 2.80 3 WB92,7C,8C • J1700+685 Radio 17: 0: 9.02 +68:30: 5.7 1.40 3 WB92,7C,8C • J1814+228 J1924+286 • WB92 J1956+635 • WB92 J2055+613 • WB92 • J2115+367 • E F • J2145+187 • WB92 J2152+653 2 WB92,8C J2202+292 • WB92 • J2208+615 Chapter 4. GB6 Short Term Variability 44 200 150 3 100 h o i M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 J0048+684 I i i i i I i i i i I i i i i I i i i t I 0 5 10 15 20 25 Time (Days) 100 r 0 ~i I I I | I i i i | i i i i | i i r J0251+562 i I 1 I I I I I I I | 1 J_ 10 20 30 Time (Days) 200 150 H 3 100 50 i i i i I i i i i I i i i i I i i i i I i i i J0049+343 E p o c h 1: IMS E p o c h 3 : 1 9 8 7 1 M I I I I I I I I I I 1 I I I I 5 10 15 20 Time (Days) 200 n — i — i — i — | — i — i — i — i — | — i — i — i — i — | — i — r J0259+516 _l I I I I L I I I i I I _L 5 10 15 Time (Days) Figure 4.6: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J0048+684, J0049+343, J0251+562, and J0259+516. Chapter 4. GB6 Short Term Variability 45 Figure 4.7: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J0502+346, J0502+388, J0532+562, and J0611+723. Chapter 4. GB6 Short Term Variability 46 Figure 4.8: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J0856+717, J0903+636, J1106+282, and J1307+064. Chapter 4. GB6 Short Term Variability 47 Figure 4.9: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J1603+110, J1630+741, J1700+685, and J1814+228. Chapter 4. GB6 Short Term Variability 48 Figure 4.10: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J1924+286, J1956+635, J2055+613, and J2115+367. Chapter 4. GB6 Short Term Variability 49 Figure 4.11: Plot of GB6 daily flux density measurements during 1986 (solid line) and 1987 (dashed line) epochs for sources J2145+187, J2152+653, J2202+292, and J2208+615. Chapter 4. GB6 Short Term Variability 50 range from 13% to 76%, with a mean value of 31%. It is apparent, from the short term flux density graphs, that each individual source varies on a wide range of time scales, perhaps due to different mechanisms, and the selected sample as a whole also includes some different time scale variation patterns. Sources such as J0251+562 and J0502+388 seem to be characterized more strongly by monthly variations where as sources like J0611+723 and J1700+685 appear to be indicative of more rapid daily fluctuations, with the majority of sources varying significantly on both monthly and daily time scales. It is difficult to physically interpret the flux density plots and the derived flux density variations. Random sampling effects and small number statistics tend to obscure the true flux density variations. However, the significant flux density variations, with associated Q confidence levels, occurring on such short time scales, warrant further detailed study, specifically with high resolution, multi-epoch, multi-frequency V L A imaging. C h a p t e r 5 R a d i o I m a g i n g w i t h t h e V L A 5 . 1 I n t e r f e r o m e t r y a n d A p e r t u r e S y n t h e s i s The Very Large Array ( V L A 1 ) is a radio telescope used for aperture synthesis, and is composed of 27 antennas arranged on a Y-shaped track, located on the San Agustin desert in New Mexico. The antennas are regularly cycled through four main configurations, known as A , B, C, and D as well as various hybrids, with a maximum extent of 36 kilometers in A configuration for high resolution imaging, down to 1 kilometer in D configuration for wide field imaging. The V L A is capable of imaging radio sources in the northern hemisphere with resolution comparable to optical telescopes, at wavelengths between 0.7 and 90 centimeters. Each of the fully steerable, parabolic reflectors of the V L A is 25 meters in diameter, with an altazimuth mount and a Cassegrain focus. Antennas are equipped with four input channels, and therefore can monitor both left and right circularly polarized radiation components at two different frequencies, within a particular band, simultaneously. The total intensity, or Stokes / parameter, can be determined from the measured polarized intensity components. I = RR* + LL* (5.1) 1 The V L A is operated by the National Radio Astronomy Observatory, which is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. 51 Chapter 5. Radio Imaging with the VLA 52 Figure 5.1: Overhead view of V L A in D configuration. The spatial distribution of radio emission from any source in the sky may be con-sidered a superposition of 2-dimensional Fourier components. Any component of the Fourier integral can be measured interferometrically by correlating the output signal from two antennas separated by an appropriate distance. A radio array with ./V anten-nas forms N(N — l ) / 2 interferometric pairs, and the V L A with 27 antennas, consists of 351 interferometers. By measuring a large number of the Fourier components, one can create an approximate reconstruction (aperture synthesis) of a source spatial intensity distribution. The V L A , with a finite number of elements, acts as a spatial filter on the sky intensity distribution, measuring particular Fourier components, determined by the projected antenna separations. The technique of aperture synthesis can be summarized as a Fourier transform of the measured auto-correlation function, or complex visibility Vu(u, v), where u and v are the projected antenna separations, expressed in wavelengths, equivalent to spatial frequencies. Figure 5.2: Close up view of a V L A antenna. Chapter 5. Radio Imaging with the VLA 54 ID(l,m) = J Jvi/(u,v)S(u,v)e2iri{ul+vm)dldm (5.2) In reality, the continuous complex visibility is only sampled, and therefore must be multiplied by a discrete sampling function S(u,v). The quality of the resultant "dirty" image, ID(l,m), is limited by the degree of sampling and the noise level in the complex visibility. The coordinates used for the image, I and m, are directional cosines of an angular position on the sky. Complex visibility is measured in units of Jansky (Jy), a flux density, and the image intensity is a surface brightness measured in Jansky per beam area, where 1 Jy = 10- 2 6 W m2 Hz The "dirty" image derived above is severely degraded by a complicated, spatially variable synthesized point spread function, making direct interpretation difficult. The "dirty" image is a convolution of a "real" image and the synthesized beam point spread function, B(l, m). I?(l,m) = Iv(l,m)*B(l,m) (5.3) Generally, the "dirty" image is iteratively deconvolved using a 'lq cleaning" algorithm, generating a source model, which is then convolved with a elliptical gaussian approxima-tion to the synthesized beam. The field of view of the resultant "clean" image is diffraction limited by the primary beam width of the individual antennas. The resolution in the image is determined by the synthesized beam width, and only structure smaller than an angular scale defined by the minimum antenna separation, can be observed. The above discussion of imaging is a simplification. As mentioned, the image qual-ity is limited by noise, both intrinsic to the equipment, and from external interference. Chapter 5. Radio Imaging with the VLA 55 Equation 5.2 assumes a coplanar array used for monochromatic observations of a planar intensity distribution. These assumption introduce radial image distortions which be-come increasingly significant further away from the pointing center. Other effects which degrade the image include atmospheric phase errors and sidelobes of the antenna recep-tion pattern, particularly with bright "confusing" sources nearby. A detailed derivation of the aperture synthesis technique, as well as an in depth discussion of distortions and image quality, is given in reference [11]. 5.2 V L A parameter selection The purpose for observing a number of variable sources with the V L A was to obtain high resolution images at two epochs, separated by approximately a month, to eluci-date any structural changes and flux variations over this time scale. Observations at two frequency bands allowed spectral index determination, as well as imaging frequency dependent structure. Two 24 hour observations in A configuration (highest resolution) were originally proposed. However only two 12 hour observations in B configuration were granted. The first 12 hour observation session (epoch A) began at 09:30 LST on March 19, 1997 followed by a second session (epoch B) at 09:30 LST on Apri l 17, 1997. The main observational strategy adopted comprised observing all 24 sources at X band (3.6 cm), a relatively sensitive frequency band, and either at U band (2 cm) for the majority of sources, or K band (1.3 cm) for the strongest sources, to take advantage of the slightly higher resolution. Important considerations for V L A parameter selection include sensitivity, image quality, and dynamic range, all of which are coupled. Clearly, one wishes to minimize the noise level, Srms, which depends on the choice of integration time, At, and bandwidth, Au, band dependent system temperature Tsys, and antenna efficiency e, as well as the number of antennas, N, and input channels, n, of the array. Chapter 5. Radio Imaging with the VLA 56 K y/N (N-l)n At Au 0 12 T (5.4) (5.5) Unfortunately, the minimum noise level achieved is restricted by the allotted time, and the image degrading effect of bandwidth smearing. A standard V L A bandwidth of 50 MHz was utilized for all observations. Approximate values of important V L A B configuration parameters are listed in table 5.1. V L A Parameters: B configuration Band X U K Wavelength (cm) 3.6 2.0 1.3 Frequency (GHz) 8.0 - 8.8 14.4 - 15.4 22 - 24 Synthesized Beam Width (arcsec) 0.7 0.4 0.3 Primary Beam Size (arcmin) 5.4 3 2 Largest Angular Scale (arcsec) 20 12 7.3 RMS 10 min Sensitivity (mJy) 0.045 0.17 0.31 System Temperature (K) 34 110 160 - 190 Antenna Efficiency (%) 63 52 45 Table 5.1: V L A Parameters in B Configuration Dynamic range, defined here as the peak surface brightness of an image, normalized by five times the noise level, is one measure of the image quality, and to a large degree determines the accuracy of flux measurements and the ability to discern faint extended emission associated with a source. Time spent per source was allocated such that the achieved dynamic range, based on GB6 flux measurements, for all sources would be > 100 at the shortest wavelength of observation. Since the V L A is a spatial filter, the detailed structure in a image is limited by the uv plane coverage. By observing each source at two different hour angles, defined by equation 5.6, greater uv sampling is achieved, resulting in improved image quality. Chapter 5. Radio Imaging with the VLA 57 Hour Angle = Local Sidereal Time — Right Ascension (5-6) A n essential part of V L A observation is absolute flux and phase calibration. The standard V L A flux calibrator 3C286 was chosen for flux amplitude calibration, and one phase calibrator was chosen, from the V L A calibrator manual [10], for each source, with the criterion that the calibrator be relatively strong, at least partially unresolved, with accurate position, and in close proximity to the source. The phase calibrators were only intended for coarse phase adjustments, since self-calibration imaging techniques were to be used. Whenever possible, phase calibrators were shared between sources for more efficient use of time. In order to observe all 24 sources and calibrators at two different hour angles and at two different frequencies, observation times were restricted to snapshots, of order a few minutes. The source observations were scheduled within the given 12 hour time slot to ensure the sources were visible above the instrumental horizon, to maximize the difference in observed hour angles, and to minimize antenna move and set up time. The actual V L A observation is controlled by a user specified parameter file, created with OBSERVE, a computer program distributed by N R A O . 5.3 I m a g i n g w i t h AIPS A software package, Astronomical Image Processing System, AIPS, has been designed by N R A O for editing, calibration, imaging and analysis of radio interferometric data, particularly suited for the V L A . Before an image can be made, the raw uv data must be edited, by flagging inconsistent baseline visibility amplitudes, and the remaining visibil-ities modified by gains computed during basic flux and phase calibration. Chapter 5. Radio Imaging with the VLA 58 A fast fourier transform (FFT) is the most computationally efficient method of in-verting the calibrated uv data. A n automated mapping and self-calibration script called MAPIT, which coordinates a' number of AIPS procedures, was used to image the V L A data. To perform the F F T , MAPIT must first interpolate the sampled uv data onto a regular, rectangular grid, then apply a user specified weighting factor based on data reliability, sample density, and a taper function, controlling synthesized beam shape. For all V L A maps generated, uniform weighting with no taper was used for best resolution. MAPIT self-calibrates each V L A image by iteratively solving for antenna gains, and then applying these to the data. Both the maximum number of iterations and image size are controlled by the user to reduce C P U time. The final, calibrated and cleaned, source model is convolved with an elliptical gaussian restoring beam, to produce a high dynamic range, snapshot image. AIPS includes a number of analysis tasks to fit elliptical gaussians for source flux density and position measurements, to integrate flux densities over specified regions, and for noise and measured parameter error estimation. The process of interpreting and decomposing an image into components involves fitting an increasing number of elliptical gaussians to flux density peaks, until no further peaks are detectable in the image residuals at some confidence level cutoff. A relatively conservative peak detection confidence cutoff at 5cr noise contour level, was adopted with obvious V L A artifacts, if present, subjectively ignored. The fitted elliptical gaussian dimensions, compared to the restoring beam dimensions, are a further check on the quality of the component decom-position. Measured component flux densities, flux density uncertainties, positions and relative positional uncertainties are determined directly from the fitted gaussians and fit-ting uncertainties. Absolute position uncertainties of the brightest component are based on relative position uncertainty and scatter of a maximum of four independent position measurements, derived from the different epoch and wavelength images, and therefore Chapter 5. Radio Imaging with the VLA 59 incorporate random V L A pointing errors. Extended emission flux densities, when ap-propriate, are integrated over a delimiting box minimally encompassing the extended flux region, with the extent usually defined by the largest contiguous 2o contour level. Various AIPS image display and contouring subroutines were used for the final image presentation. r Chapter 6 Results and Conclusion The V L A images and data presented in this chapter are the culmination of careful selec-tion of sources from the GB6 catalog believed to exhibit short term variability, and with no previous identification. Of the 24 sources imaged, 11 are at least partially resolved, 12 are unresolved, and one source did not appear in V L A imaged region, most likely due to inaccurate GB6 position. The majority of these sources is expected to be extragalactic. It was hoped that some of these sources will show significant structural variation or further evidence of extreme variability, consistent with either a galactic object, or interesting highly beamed sub-class of extragalactic objects. 6.1 Resolved Sources The 11 resolved sources show varying levels of detail and are divided into three groups based on general physical appearance. The division, used here for convenience, is some-what arbitrary, as one expects an underlying continuum in morphology, based on unified beam models for AGN's , and image structure must be interpreted in the context of achieved sensitivity and resolution. Any classification of these objects, without further study is only speculative. 60 Chapter 6. Results and Conclusion 61 Figure 6.1: V L A images of J0049+343 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32 times the noise level. Chapter 6. Results and Conclusion 62 Figure 6.2: V L A images of J0259+516 at X band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256, 512 times the noise level. Chapter 6. Results and Conclusion 63 Figure 6.3: V L A images of J0532+562 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256, 512, 1024 times the noise level. Chapter 6. Results and Conclusion 64 Chapter 6. Results and Conclusion 65 Figure 6.5: V L A images of JT307+064 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256 times the noise level. Chapter 6. Results and Conclusion 66 Figure 6.6: V L A images of J1630+741 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256 times the noise level. Chapter 6. Results and Conclusion 67 E p o c h A E p o c h B S O U R C E B A N D N o i s e D y n a m i c B e a m A x i s P . A . N o i s e D y n a m i c B e a m A x s P . A . (fJv/b) R a n g e ( ircsec ) (deg) R a n g e ( arcsec] (deg) J0048+684 X 205 138 1.24 X 0.70 92 125 239 1.17 X 0.70 96 U 197 120 0.66 X 0.39 90 196 120 0.61 X 0.38 96 J0049+343 X 114 5 1.13 X 0.79 96 98 6 1.12 X 0.74 104 u 206 3 0.57 X 0.46 96 192 3 0.57 X 0.39 99 J0251+562 X 125 617 1.60 X 0.69 105 113 628 1.54 X 0.69 109 K 457 180 0.57 X 0.24 102 506 129 0.52 X 0.26 107 J0259+516 X 78 183 1.56 X 0.70 104 79 157 1.50 X 0.68 108 u 212 63 0.85 X 0.39 102 197 61 0.80 X 0.36 108 J0502+346 X 115 369 1.41 X 0.77 73 133 239 1.37 X 0.73 70 u 217 237 0.81 X 0.40 79 276 120 0.73 X 0.38 72 J0502+388 X 356 128 1.35 X 0.74 78 86 493 1.31 X 0.72 73 u 242 209 0.79 X 0.42 82 308 137 0.70 X 0.39 76 J0532+562 X 82 253 1.35 X 0.71 85 92 210 1.26 X 0.70 81 u 180 123 0.75 X 0.38 87 221 95 0.64 X 0.37 84 J0611+723 X 92 248 1.24 X 0.70 77 91 224 1.20 X 0.70 73 u 1201 20 0.67 X 0.36 79 226 82 0.58 X 0.36 80 J0856+717 X 104 232 1.02 X 0.74 111 133 214 0.99 X 0.73 105 u 216 175 0.59 X 0.40 112 269 140 0.52 X 0.40 113 J0903+636 X 74 7 1.04 X 0.70 116 72 8 0.99 X 0.70 109 u 182 1 0.56 X 0.36 117 172 1 0.50 X 0.36 115 J1106+282 X 180 325 0.81 X 0.79 167 123 471 0.81 X 0.75 77 K 341 150 0.31 X 0.25 159 413 130 0.28 X 0.27 133 J1307+064 X 91 82 0.94 X 0.75 3 87 84 0.87 X 0.76 7 u 202 14 0.50 X 0.40 162 188 15 0.43 X 0.41 174 J1603+110 X 133 674 0.99 X 0.81 150 129 709 0.94 X 0.78 140 K 554 160 0.36 X 0.29 159 612 145 0.34 X 0.28 132 J1630+741 X 92 55 0.98 X 0.73 53 89 54 0.89 X 0.76 48 u 206 14 0.51 X 0.40 28 176 17 0.47 X 0.38 36 J1700+685 X 102 430 0.92 X 0.75 54 125 416 0.85 X 0.76 53 K 675 105 0.32 X 0.25 43 743 102 0.31 X 0.26 53 J1814+228 X 77 53 0.96 X 0.80 • 129 72 58 1.00 X 0.74 120 u 168 17 0.55 X 0.44 135 171 17 0.51 X 0.39 118 J1924+286 X 74 108 0.87 X 0.82 99 71 122 0.89 X 0.77 107 u 195 44 0.48 X 0.46 175 181 51 0.46 X 0.41 99 J1956+635 X 90 158 1.07 X 0.74 117 87 164 1.00 X 0.73 113 u 192 64 0.53 X 0.42 112 201 60 0.47 X 0.39 109 J2055+613 X 99 740 1.01 X 0.73 81 164 448 0.98 X 0.73 86 K 512 124 0.35 X 0.26 72 691 97 0.34 X 0.26 84 J211S+367 X 88 238 1.02 X 0.79 93 92 184 1.03 X 0.74 104 u 211 116 0.52 X 0.46 97 233 104 0.52 X 0.39 101 J2145+187 X 96 173 1.01 X 0.82 126 72 243 0.97 X 0.78 122 u 182 94 0.53 X 0.45 145 198 84 0.50 X 0.41 118 J2202+292 X 82 122 0.90 X 0.82 95 70 143 0.91 X 0.76 108 u 175 30 0.47 X 0.46 152 183 28 0.47 X 0.41 98 J2208+615 X 82 121 1.08 X 0.72 94 85 111 1.01 X 0.73 92 u 188 33 0.55 X 0.42 84 189 32 0.53 X 0.38 95 Table 6.1: Image quality information for sources observed with the V L A . Achieved noise levels, five sigma dynamic range, and restoring beam parameters are listed for both observing bands and epochs. Chapter 6. Results and Conclusion 68 6.1.1 Two-Sided Sources There are four sources, J0049+343, J1307+064, J0532+562 and J1630+741, which have distinct, two-sided structure, and appear to be typical radio galaxies. With the excep-tion of J0049+343, all sources posses a strong central region; however only the core of J0532+562 has a self absorbed flat spectrum, possibly indicating that the steep spectrum central regions of J1630+741 and J1307+064 are not sufficiently resolved and contain sig-nificant extended emission. The central region of J0049+343, noticeably absent, may be obscured by a parent galaxy. Two prominent jets are apparent in J0049+343 at X band, with the stronger jet, to the north, also apparent at U band, having a flat spectrum. Both J0532+562 and J1630+741 show evidence for a single jet to the northwest and northeast respectively. The jet of J0532+562 is not visible at U band, whereas the jet of J1630+741 is more clearly resolved at U band, although not fully separated from the steep spectrum extended Chapter 6. Results and Conclusion 69 Figure 6.8: V L A images of J1956+635 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256, 512 times the noise level. Chapter 6. Results and Conclusion 70 J 0 0 4 9 + 3 4 3 C O M P O N E N T FXA FXB FUA FUB » B VX Vu SR.A. 6Dec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 3.0 3.0 2.7 3.2 0.22 -0.13 0.005 0.096 0.000 0.000 ± 0.4 0.3 0.7 0.7 0.52 0.41 0.086 0.164 0.027 0.020 Extended 90.7 88.5 10.1 29.9 3.86 1.91 0.013 0.496 ± 2.8 3.1 6.1 6.4 1.06 0.38 0.023 0.252 Total 93.8 91.5 12.8 33.2 3.51 1.78 0.012 0.444 ± 2.7 3.1 6.1 6.4 0.84 0.34 0.022 0.214 J 0 5 3 2 + 5 6 2 C O M P O N E N T FXA FXB FUA FUB a A, Vx Vu SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 103.3 96.5 110.8 104.2 -0.12 -0.14 0.034 0.030 0.000 0.000 ± 0.3 0.3 0.6 0.8 0.01 0.01 0.002 0.005 0.007 0.006 b 5.2 4.8 2.4 2.3 1.37 1.26 0.042 0.011 -3.990 7.485 ± 0.4 0.4 0.8 1.0 0.57 0.80 0.053 0.273 0.022 0.012 c 2.2 1.8 0.0 0.0 0.099 -0.625 1.064 ± 0.3 0.4 0.9 1.1 0.138 0.044 0.037 Extended 5.8 7.8 0.0 0.0 0.146 ± 1.4 1.8 3.1 4.2 0.179 Total 116.4 110.8 113.1 106.6 0.05 0.07 0.025 0.030 ± 1.3 1.7 1.2 1.3 0.03 0.03 0.009 0.008 J 1 3 0 7 + 0 6 4 C O M P O N E N T FXA FXB FUA FUB OtA O.B VX Vu SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 52.4 52.2 23.9 23.5 1.38 1.40 0.001 0.008 0.000 0.000 ± 0.4 0.4 0.9 0.9 0.07 0.06 0.005 0.026 0.001 0.008 b 37.9 38.0 19.7 20.5 1.15 1.08 0.001 0.021 -13.383 5.447 ± 0.5 0.5 1.8 1.8 0.16 0.15 0.010 0.063 0.013 0.005 c 2.8 2.7 1.5 1.6 1.14 0.91 0.007 0.058 -8.010 2.793 ± 0.4 0.3 0.6 0.6 0.78 0.72 0.089 0.288 0.016 0.017 Extended 14.2 11.0 9.2 9.6 0.77 0.24 0.129 0.021 ± 2.5 2.3 6.4 6.8 1.26 1.29 0.137 0.494 Total 107.3 103.9 54.2 55.3 •1.20 1.11 0.016 0.009 ± 2.4 2.2 6.1 6.4 0.20 0.21 0.015 0.081 J 1 6 3 0 + 7 4 1 C O M P O N E N T FXA FXB FUA FUB <*A dB Vx Vu SR.A. SDec. (mJy) (mJy) (mJy) (rnJy) (asec) (asec) a 35.3 34.7 19.2 18.7 1.07 1.09 0.009 0.016 0.000 0.000 ± 0.4 0.4 0.8 0.7 0.08 0.07 0.008 0.028 0.013 0.010 Extended 45.9 41.3 21.8 20.8 1.31 1.20 0.053 0.022 ± 2.0 1.9 3.6 3.8 0.30 0.33 0.032 0.123 Total 81.2 75.9 41.0 39.5 1.20 1.15 0.033 0.019 ± 1.9 1.9 3.5 3.7 0.16 0.17 0.017 0.064 Table 6.2: Measured parameters of two-sided resolved sources, including flux density, Fij, spectral index, ctj, and variability index, Vi, at i band during epoch j, as well as relative positions, for source components. Chapter 6. Results and Conclusion 71 21 1540.60 40.55 40.50 40.45 40.40 40.35 40.30 40.25 40.20 21 15 40.60 40.55 40.50 40.45 40.40 40.35 40.30 40.25 RIGHT ASCENSION (J2000) RIGHT ASCENSION (J2000) Figure 6.9: V L A images of J2115+367 at X band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256, 512, 1024 times the noise level. emission. There is no evidence for a jet emanating from the core at either X or U band in J1307+064. A l l four sources have two obvious radio lobes at X band, whereas only J1307+064 has both lobes, and J0532+562 has one lobe, apparent at U band. In all cases, these lobes are steep spectrum, with one lobe being noticeably brighter than the other. The X band radio lobes of J1630+741 differ from one another. The inner part of the lobe to the southeast, correlated to the jet like structure obvious at U band, is compact and bright near the core, but the lobe becomes very tenuous as it curves further south. The lobe to the west of the core does not have an analogous compact feature near the core at either X or U band, but the lobe is much larger and brighter than the outer region of the southern lobe, and actually has a peak in the the flux at the western edge of the lobe, far from the core. The radio lobes of J0049+343 and J1630+741 are relatively detailed, compared to the compact lobes of J1307+064 and J0532+562, implying either intrinsically larger Chapter 6. Results and Conclusion 72 Figure 6.10: V L A images of J2145+187 at X and U band during epoch A and B as labeled. Contour levels are 3, 4; 5, 6, 8, 16, 32, 64, 128, 256, 512, 1024 times the noise level. Chapter 6. Results and Conclusion 73 Figure 6.11: V L A images of J2202+292 at X and U band during epoch A and B as labeled. Contour levels are 3, 4, 5, 6, 8, 16, 32, 64, 128, 256, 512 times the noise level. Chapter 6. Results and Conclusion 74 lobes for the former pair of sources, or greater distance for the latter pair. The overall structure of J1307+064 is linear, whereas for both J0049+343 and J0532+562 the radio lobes are slightly out of alignment from the central region, and in contrast, the structure of -11630+741 is extremely non-symmetric. These structural asymmetries may be the result of motion of the central galaxy or precession of the jet. In all four cases there is no significant flux density variations or spectral index changes observed. Sig-nificant flux density variation is defined here as a variability index, V / > 0 . 1 a t a > 5 sigma confidence level, a moderate flux density variation is defined by a variability index between 0.10 and 0.05 also at a > 5 sigma confidence level, and a significant spectral index change is one detected at a > 3 sigma level. 6.1.2 One-Sided Sources Three of the 24 sources imaged with the V L A , at X band, exhibit one-sided structure associated with the central region, including a single radio lobe, and some evidence for a jet. Both J1956+635 and J2202+292 are strongly dominated by the central region, with the lobes representing only a small fraction of the total flux. Both the central region and the lobe of J0903+636 are extremely weak and the lobes of all three sources are of the order of 5 mJy. J2202+292 has an obvious extension from the core towards the lobe, and J0903+636 includes some residuals between the core and the lobe that may represent knots of the jet. The apparent proximity of the lobes to the core in J1956+635 obscures any sign of a jet. At U band, only a central core is visible in J0903+636 and J2202+292, both having a steep spectrum, which again may indicate inclusion of extended emission in the central feature. Although no radio lobe of J1956+635 is observed at U band, the central region is now clearly resolved into two flat spectrum components, perhaps a true core and an approaching jet, or both an approaching and receding jet. Since the central region is Chapter 6. Results and Conclusion 75 J0903+636 C O M P O N E N T Fx A FXB FUA FUB <*A Vx Vu 8R.A. SDec. (mJy) (mJy) {mJy) (mJy) (asec) (asec) a 4.3 4.5 1.5 1.1 1.81 2.41 0.018 0.152 0.000 0.000 ± 0.3 0.3 0.9 0.8 1.00 1.27 0.052 0.454 0.019 0.014 Extended 5.1 5.2 0.0 0.0 0.004 ± 0.7 0.8 1.3 1.6 0.102 Total 9.5 9.7 1.5 1.1 3.18 3.76 0.010 0.152 ± 0.6 0.7 0.9 0.8 0.99 1.27 0.049 0.454 J 1 9 5 6 + 6 3 5 C O M P O N E N T FXA FXB FUA FUB <*A a s VX Vu SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) au 37.0 37.9 27.7 26.9 0.51 0.60 0.013 0.014 0.000 0.000 ± 0.2 0.2 0.7 0.7 0.05 0.05 0.004 0.018 0.007 0.010 bu 46.2 47.4 34.3 33.9 0.52 0.59 0.013 0.005 0.291 0.237 ± 0.2 0.2 0.7 0.7 0.04 0.04 0.004 0.014 0.012 0.012 cx 83.2 85.4 62.0 60.9 0.52 0.59 0.013 0.009 0.123 0.104 ± 0.3 0.3 0.9 1.0 0.03 0.03 0.003 0.011 0.020 0.001 Extended 4.8 5.1 0.0 0.0 0.031 ± 1.1 1.1 2.2 2.3 0.161 Total 88.0 90.5 62.0 60.9 0.62 0.70 0.014 0.009 ± 1.1 1.1 0.9 1.0 0.03 0.04 0.009 0.011 J 2 2 0 2 + 2 9 2 C O M P O N E N T FXA FXB FUA FUB OiA CtB VX Vu SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 51.2 51.3 26.8 26.5 1.14 1.16 0.001 0.007 0.000 0.000 ± 0.3 0.2 0.6 0.6 0.04 0.04 0.004 0.017 0.006 0.002 b 3.4 3.8 1.5 0.9 1.43 2.51 0.046 0.256 0.152 -0.971 ± 0.3 0.3 0.6 0.7 0.71 1.43 0.067 0.380 0.020 0.016 c 3.1 3.4 0.0 0.0 0.050 3.774 -4.993 ± 0.3 0.3 0.9 0.9 0.068 0.016 0.017 Extended 2.1 1.7 5.7 0.5 -1.79 2.16 0.095 0.839 ± 1.2 1.1 2.2 2.8 1.21 9.84 0.426 0.668 Total 59.8 60.1 34.1 27.9 0.99 1.35 0.003 0.100 ± 1.0 1.0 2.1 2.6 0.11 0.17 0.012 0.053 Table 6.3: Measured parameters of one-sided resolved sources, including flux density, Fij, spectral index, aj, and variability index, Vi, at % band during epoch j, as well as relative positions, for source components. Chapter 6. Results and Conclusion 76 resolved into two components at U band and not at X band, only the components specified by a band subscript in table 6.3 are real. For analysis purposes, the X band central component has been artificially divided, in proportion to the U band component pair, and an artificial U band single component is the sum of the real U band pair. It is tempting to interpret these three sources as either more distant or intrinsically weaker examples of two-sided sources, owing to the relatively faint observed radio lobe, for which the differential relativistic doppler brightening has conspired to boost only one side of the structure above the sensitivity threshold. Like the previous two-sided objects, the one-sided objects do not show any significant flux density variations or any certain change in spectral index. 6.2 Partially Resolved Sources Four of the resolved sources, J0259+516, J2145+187, J2115+367 and J1700+685, do not clearly fall into either of the preceding categories, and elude interpretation. A l l of these sources exhibit some structure, which appears to be different in both epochs, and all show approximately at least a three sigma change in spectral index. Both J1700+685 and J2115+367 are significantly variable at X band, J0259+516 is moderately variable at X band, and J2145+187 does not show significant flux density variation at either band. Of the four sources, the most intriguing is J1700+6851, which consists of a bright core and a second component to the west-northwest of the core. Both components brighten during epoch B, but since the second component is within the central beam of the core, interpretation is difficult. Due to the ambiguous and changing structure, observed flux density variations, and interesting spectral index changes, all four of these sources deserve to be imaged by the V L A in A configuration and perhaps require higher resolution 1 A n optical spectrum taken in August, 1997 with the C H F T places J1700+685 at a redshift of z ~ 0.3, with prominent emission lines and absorption features commensurate with a quasar. Chapter 6. Results and Conclusion 77 V L B A / V L B I imaging and optical wavelength study. 6 .3 U n r e s o l v e d S o u r c e s Half of the sources imaged with the V L A were unresolved at both observed bands. The flux density measurements, as well as the spectral index and variability information for these sources is summarized in table 6.5. The majority of the 12 sources shows no significant flux density variation, and only J0502+346 shows significant variation at both bands, while both J0251+562 and J0611+723 show significant variation only at K and U bands respectively. Moderate variation at X band occurs in J0856+717 and J0611+723, while moderate variation occurs at U band for J0502+388. The spectra of most of the sources is flat (—0.5 < a < 0.5) but J2208+615 and J1814+228 have steep spectra (a > 0.5) whereas J0856+717 has an inverted spectrum (a < —0.5). Eight of the twelve sources exhibit a change in spectral index at the three sigma level or higher. 6 . 4 APS a n d DSS O p t i c a l C o u n t e r p a r t s With substantially more accurate positions for all V L A imaged sources, it is possible to convincingly associate optical counterparts. The digitized DSS POSS I plates were checked for optical counterparts within five arcseconds of the V L A derived radio positions. The matching of sources is limited by the positional accuracy of the plates, which have not been calibrated. Table 6.6 contains an approximate separation between radio and optical positions and qualitative description of optical counterpart quality and DSS image noise level. Chapter 6. Results and Conclusion 78 J 0 2 5 9 + 5 1 6 C O M P O N E N T FXA FXB FUA FUB CtA OCB VX Vu SR.A. SDec. (mJy) (mJy) (mJy) {mJy) (asec) (asec) a 71.2 61.7 66.5 61.0 0.12 0.02 0.071 0.043 0.000 0.000 ± 0.3 0.3 0.7 0.7 0.02 0.02 0.003 0.008 0.009 0.003 b 1.5 2.0 0.0 0.0 0.128 -0.375 0.854 ± 0.4 0.5 1.0 1.0 0.193 0.179 0.105 Total 72.7 63.7 66.5 61.0 0.16 0.08 0.066 0.043 ± 0.5 0.6 0.7 0.7 0.02 0.03 0.006 0.008 J 1 7 0 0 + 6 8 5 C O M P O N E N T FXA FXB FKA FKB CCA OCB VX VK SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 223.6 269.1 361.8 386.5 -0.49 -0.37 0.092 0.033 0.000 0.000 ± 0.4 0.4 2.4 2.6 0.01 0.01 0.001 0.005 0.002 0.004 b 3.9 17.0 0.0 0.0 0.624 -0.263 0.210 ± 0.3 0.6 3.3 3.7 0.043 0.146 0.066 Total 227.5 286.0 361.8 386.5 -0.47 -0.31 0.114 0.033 ± 0.7 0.8 5.3 5.8 0.02 0.02 0.002 0.011 J 2 1 1 5 + 3 6 7 C O M P O N E N T FXA FXB FUA FUB OCA OCB VX Vu SR.A. SDec. (mJy) (mJy) (mJy) (rnJy) (asec) (asec) a 105.4 83.8 121.5 119.2 -0.25 -0.62 0.114 0.009 0.000 0.000 ± 0.3 0.3 0.7 0.8 0.01 0.01 0.002 0.004 0.009 0.001 Extended 1.2 0.9 0.0 0.0 0.124 ± 1.0 1.0 2.0 2.1 0.686 Total 106.6 84.8 121.5 119.2 -0.23 -0.60 0.114 0.009 ± 0.9 1.0 0.7 0.8 0.02 0.02 0.007 0.004 J 2 1 4 5 + 1 8 7 C O M P O N E N T FXA FXB FUA FUB CCA OCB VX Vu SR.A. SDec. (mJy) (mJy) (mJy) (mJy) (asec) (asec) a 85.1 88.2 86.5 82.9 -0.03 0.11 0.017 0.021 0.000 0.000 ± 0.3 0.2 0.6 0.7 0.01 0.02 0.002 0.006 0.002 0.004 Extended 3.2 3.8 1.4 1.2 1.44 1.98 0.091 0.061 ± 0.7 0.5 1.5 1.7 1.96 2.41 0.125 0.860 Total 88.3 92.0 87.9 84.1 0.01 0.16 0.020 0.022 ± 0.6 0.5 1.4 1.5 0.03 0.03 0.004 0.012 Table 6.4: Measured parameters of partially resolved sources, including flux density, Fij, spectral index, cij, and variability index, Vi, at i band during epoch j, as well as relative positions, for source components. Chapter 6. Results and Conclusion 79 S O U R C E BANDS F 1 A FIB F2A F2B a A OB Vi v 2 (mJy) (mJy) (mJy) (mJy) J0048+684 X U 143.9 150.2 118.3 117.4 0.34 0.43 0.022 0.003 ± 0.7 0.4 0.7 0.7 0.01 0.01 0.003 0.004 J0251+562 X K 384.5 355.0 411.2 329.0 -0.07 0.08 0.040 0.111 ± 0.4 0.4 1.6 1.8 0.00 0.01 0.001 0.003 J0502+346 X U 211.9 159.4 256.9 165.2 -0.34 -0.06 0.141 0.217 ± 0.4 0.5 0.8 0.9 0.01 0.01 0.002 0.003 J0502+388 X U 229.1 213.2 252.8 211.8 -0.17 0.01 0.036 0.088 ± 1.2 0.3 0.8 1.1 0.01 0.01 0.003 0.003 J0611+723 X U 114.1 100.8 121.8 93.6 -0.12 0.13 0.062 0.131 ± 0.3 0.3 4.2 0.8 0.06 0.02 0.002 0.022 J0856+717 X U 120.0 141.1 188.7 188.5 -0.80 -0.51 0.081 0.001 ± 0.4 0.5 0.8 0.9 0.01 0.01 0.002 0.003 J1106+282 X K 293.2 289.0 256.0 269.6 0.14 0.07 0.007 0.026 ± 0.6 0.4 1.2 1.4 0.01 0.01 0.001 0.004 J1603+110 X K 448.3 458.0 446.0 449.4 0.01 0.02 0.011 0.004 ± 0.5 0.4 1.9 2.1 0.00 0.00 0.001 0.003 J1814+228 X U 20.8 20.7 14.4 15.0 0.65 0.56 0.002 0.022 ± 0.3 0.2 0.6 0.6 0.07 0.07 0.009 0.028 J1924+286 X U 40.3 43.2 42.5 46.9 -0.09 -0.14 0.035 0.049 ± 0.3 0.2 0.7 0.6 0.03 0.03 0.004 0.010 J2055+613 X K 364.6 367.8 317.2 336.7 0.14 0.09 0.004 0.030 ± 0.3 0.6 1.8 2.4 0.01 0.01 0.001 0.005 J2208+615 X U 49.6 47.5 31.2 30.4 0.81 0.79 0.021 0.014 ± 0.3 0.3 0.6 0.6 0.04 0.04 0.004 0.015 Table 6.5: Measured parameters of unresolved sources, including flux density F^, spectral index aj, and variability index Vi, at the ith band listed in the second column of the table, during epoch j. The automated plate scanner (APS) is a project undertaken by the University of Min-nesota to catalog objects on the digitized POSS I plates, and the current data has been made available. The APS project is attempting to classify, provide calibrated positions, and measure magnitude and colour for every object on the POSS I plates. To date, only a fraction of the work has been completed, but three of the V L A imaged radio sources have APS optical counterparts within three arcseconds. The APS derived parameters for these three radio sources are given in table 6.7. A more complete description of the APS project and the DSS plates can be found in section 4.2.3. 6.5 C o n c l u s i o n The project goal of taking high resolution multi-epoch, multi-frequency V L A images of the 24 selected GB6 short term radio variables was achieved, with no major problems occurring during observations and resulting image quality parameter values (table 6.1) Chapter 6. Results and Conclusion 80 S O U R C E N A M E APosition (arcsec) Object Quality Noise Level J0048+684 1.8 faint high J0049+343 4.0 bright low J0251+562 2.2 bright high J0259+516 empty low J0502+346 empty low J0502+388 empty low J0532+562 1.4 faint low J0611+723 empty medium J0856+717 2.4 bright medium J0903+636 empty high J1106+282 1.4 faint low J1307+064 empty medium J1603+100 1.0 bright low J1630+741 3.4 moderate medium J1700+685 0.5 bright low J1814+228 empty low J1924+286 3.8 bright medium J1956+635 2.2 bright low J2055+613 empty low J2115+367 empty low J2145+187 empty low J2202+292 empty medium J2208+615 3.1 moderate medium Table 6.6: DSS optical counterparts of imaged radio sources. A n approximate separation of measured radio and optical positions, as well as a qualitative description of object quality and noise level on the POSS I images is listed S O U R C E Class Probability APosition APS Position Magnitude Color N A M E % (arcsec) (J2000) (O) (O-E) J0049+343 Galaxy 92 2.942 0:49:45.47 +34:22:35.90 21.42 3.20 J0856+717 Star 93 1.386 8:56:54.83 +71:46:22.52 19.65 0.52 J1700+685 Galaxy 80 0.540 17:00:09.36 +68:30:06.59 20.44 1.40 Table 6.7: APS determined parameter of DSS POSS I optical counterparts of imaged radio sources. Listed is the APS classification with associated probability, separation of radio and optical objects, calibrated position, magnitude, and colour. Chapter 6. Results and Conclusion 81 S O U R C E B A N D S P o s i t i o n ( J 2 0 0 0 ) Fl F2 a A a v% V „ (mJy) (mJy) J 0 0 4 8 + 6 8 4 X U 0: 4 8 : 3 5 . 9 8 1 1 + 6 8 : 2 6 : 2 7 . 1 0 1 147 .8 1 1 7 . 9 0 . 3 9 0 . 0 9 2 . 8 1 4 .2 ± 0 . 0 0 0 5 0 . 0 0 4 2 .0 0 .5 0 . 0 3 0 .02 1.21 J 0 0 4 9 + 3 4 3 X U 0: 4 9 : 4 5 . 4 7 1 1 + 3 4 : 2 2 : 3 2 . 9 5 8 9 2 . 7 22 .7 2 .28 1.72 1 0 . 7 2 1.4 ± 0 . 0 0 2 2 0 . 0 2 0 2 .0 7.2 0 . 4 6 0 . 9 0 8 .20 J 0 2 5 1 + 5 6 2 X K 2: 5 1 : 5 4 . 6 2 8 3 + 5 6 : 1 6 : 1 9 . 5 2 4 3 6 9 . 0 3 7 2 . 3 - 0 . 0 1 0 .15 10 .80 42 .9 ± 0 . 0 0 1 9 0 . 0 0 1 10.4 2 8 . 9 0 .05 0 . 0 1 2 .70 J 0 2 5 9 + 5 1 6 X U 2: 5 9 : 3 8 . 3 2 9 3 + 5 1 : 3 8 : 1 3 . 8 3 1 6 8 . 6 6 3 . 7 0 .12 0 .08 1 1 . 2 7 8 .7 ± 0 . 0 0 1 0 0 . 0 0 3 3.2 1.9 0 .03 0 .03 1.56 J 0 5 0 2 + 3 4 6 X U 5: 2 : 2 9 . 9 3 9 7 + 3 4 : 3 6 : 3 4 . 5 9 4 187 .5 2 1 6 . 4 - 0 . 2 4 0 .28 3 3 . 2 4 8 0 . 9 ± 0 . 0 0 0 7 0 . 0 0 8 18 .4 3 1 . 8 0 . 0 9 0 . 0 1 4 . 5 6 J 0 5 0 2 + 3 8 8 X U 5: 2 : 3 2 . 4 8 7 1 + 3 8 : 4 9 : 5 4 . 9 5 6 216 .3 2 3 4 . 8 - 0 . 0 7 0 .18 12 .43 2 1 . 3 ± 0 . 0 0 0 9 0 . 0 0 7 3.0 14 .2 0 . 0 6 0 . 0 1 3 .56 J 0 5 3 2 + 5 6 2 X U 5: 3 2 : 5 9 . 6 6 6 2 + 5 6 : 1 2 : 2 2 . 6 6 1 114 .0 109 .9 0 . 0 6 0 .02 5 .46 3.1 ± 0 . 0 0 0 9 0 . 0 0 6 1.9 2.3 0 .02 0 .04 1.23 J 0 6 1 1 + 7 2 3 X U 6 1 1 : 9 . 1 6 8 6 + 7 2 : 1 8 : 1 5 . 6 1 9 107.4 9 8 . 1 0 . 0 8 0 .25 1 3 . 8 0 18 .2 ± 0 . 0 0 2 8 0 . 0 0 2 4 .7 4 .4 0 .05 0 . 0 6 1.42 J 0 8 5 6 + 7 1 7 X U 8: 5 6 : 5 4 . 8 6 9 1 + 7 1 : 4 6 : 2 3 . 8 9 4 129 .3 1 8 8 . 7 - 0 . 6 7 0 . 2 9 9 .56 18 .1 ± 0 . 0 0 0 7 0 . 0 0 3 7.3 0 .6 0 .10 0 . 0 1 5 .50 J 0 9 0 3 + 6 3 6 X U 9 3 : 3 7 . 8 8 5 5 + 6 3 : 3 8 : 1 3 . 4 8 6 9.5 1.3 3 .43 0 . 5 8 4 . 8 8 0 .3 ± 0 . 0 0 2 8 0 .014 0.5 0 .6 0 .79 1.61 12 .48 J 1 1 0 6 + 2 8 2 X K 11 6: 7 . 2 5 4 9 + 2 8 : 1 2 : 4 6 . 8 7 8 2 9 0 . 7 2 6 2 . 1 0 . 1 1 0 . 0 7 2 .44 6 .4 ± 0 . 0 0 0 9 0 . 0 0 6 1.4 4 .8 0 .02 0 . 0 1 0 .95 J 1 3 0 7 + 0 6 4 X U 13 7: 6 . 8 5 1 0 + 6 : 2 7 : 4 6 . 7 5 4 105 .5 5 4 . 7 1.15 0 .09 3 .02 0 .6 ± 0 . 0 0 0 1 0 . 0 0 8 1.6 4 .4 0 .14 0 .29 3 .65 J 1 6 0 3 + 1 1 0 X K 16 3 : 4 1 . 9 3 1 1 + 1 1 : 5 : 4 8 . 6 5 2 4 5 3 . 2 4 4 7 . 6 0 . 0 1 0 . 0 1 1.88 8 .1 ± 0 . 0 0 0 8 0 . 0 0 3 3.4 1.4 0 . 0 0 0 . 0 1 0 .24 J 1 6 3 0 + 7 4 1 X U 16: 3 0 : 2 6 . 8 7 4 6 + 7 4 : 9 : 3 3 . 5 0 9 78 .5 4 0 . 3 1.18 0 .05 6 . 0 7 1.1 ± 0 . 0 0 3 1 0 . 0 1 0 1.9 2.6 0 .12 0 .23 3 .81 J 1 7 0 0 + 6 8 5 X K 17 0: 9 . 2 9 5 0 + 6 8 : 3 0 : 6 . 9 9 2 255 .2 3 7 3 . 6 - 0 . 3 9 0 .17 2 0 . 2 1 2 9 . 1 ± 0 . 0 0 0 3 0 . 0 0 4 20 .6 8 .7 0 . 0 6 0 .02 2 .66 J 1 8 1 4 + 2 2 8 X U 18 14 : 3 . 0 6 2 5 + 2 2 : 4 8 : 5 4 . 1 0 5 20 .7 14 .7 0 . 6 0 0 . 0 9 1.36 0 .5 ± 0 . 0 0 0 1 0 . 0 1 3 0 .2 0.4 0 .05 0 . 1 0 1.91 J 1 9 2 4 + 2 8 6 X U 19: 2 4 : 1 5 . 6 2 8 3 + 2 8 : 3 7 : 5 2 . 5 7 6 41 .8 4 4 . 8 - 0 . 1 2 0 .05 7 .90 6.5 ± 0 . 0 0 0 1 0 . 0 0 1 1.0 1.6 0 .02 0 .04 0 . 8 6 J 1 9 5 6 + 6 3 5 X U 19 : 5 6 : 2 5 . 4 7 9 5 + 6 3 : 3 2 : 4 6 . 0 4 4 8 9 . 2 6 1 . 4 0 . 6 6 0 .08 2 .38 1.2 ± 0 . 0 0 1 0 0 . 0 1 0 0 .9 0 .7 0 . 0 3 0 .05 1.37 J 2 0 5 5 + 6 1 3 X K 2 0 : 5 5 : 3 8 . 8 3 5 4 + 6 1 : 2 2 : 0 . 6 1 6 3 6 5 . 8 3 2 5 . 5 0 .12 0 .05 1.72 5 .7 ± 0 . 0 0 0 5 0 . 0 0 4 1.0 6 .7 0 .02 0 . 0 1 0 .83 J 2 1 1 5 + 3 6 7 X U 2 1 : 1 5 : 4 0 . 3 9 7 8 + 3 6 : 4 5 : 5 0 . 6 5 8 9 5 . 9 120 .4 - 0 . 3 9 0 . 3 7 9 .95 9 .1 ± 0 . 0 0 0 8 0 . 0 0 1 7.7 0 .8 0 .13 0 . 0 3 6 .84 J 2 1 4 5 + 1 8 7 X U 2 1 : 4 5 : 1 4 . 3 7 0 8 + 1 8 : 4 5 : 1 9 . 6 4 3 9 0 . 4 8 6 . 1 0 .08 0 .15 4 . 1 3 3.2 ± 0 . 0 0 0 1 0 . 0 0 4 1.3 1.3 0 .05 0 . 0 5 0 .90 J 2 2 0 2 + 2 9 2 X U 22 2: 4 . 6 3 3 1 + 2 9 : 1 4 : 5 2 . 7 9 4 6 0 . 0 3 1 . 3 1.13 0 .37 4 . 1 0 1.1 ± 0 . 0 0 0 5 0 .002 0 .7 2.2 0 .12 0 .20 3 .40 J 2 2 0 8 + 6 1 5 X U 22 8 : 1 1 . 9 1 3 9 + 6 1 : 3 2 : 5 6 . 4 4 1 4 8 . 6 3 0 . 8 0 .80 0 .02 3 .93 3 .0 ± 0 . 0 0 1 1 0 . 0 0 8 0 .7 0 .5 0 .03 0 .05 0 .93 Table 6.8: Summary of characteristic parameters for V L A imaged radio sources. Weighted average of brightest source component position is listed, along with weighted average of total flux, Fj, at the ith band. Also listed are the characteristic spectral index, change in spectral index, variability expressed as a percentage (eqn. 1.2), and variability confidence level (eqn. 1.4). Chapter 6. Results and Conclusion 82 obtained as planned. In particular, a resolution of the order of 1" at X band and < 1" for U or K band, slightly larger than the ideal values in table 5.1, were achieved as expected. Although U or K band observations were necessary to derive spectral indices, they were not as useful as originally hoped in elucidating source structure, compared to X band. It was thought that the improved resolution at U or K band would offset the loss of sensitivity and increase in V L A system noise at U or K band with respect to X band, and maintain importance for structure determination. Generally, this was not the case, especially for steep spectrum extended structure, and it is suggested that future similar V L A based variability studies rely primarily on X band observations, and use U or K band observations only for sources for which it is necessary. Of the 24 radio sources imaged at X band four had distinct two-sided structure and three had one-sided structure, none of which exhibited significant variability in structure, flux density variation, or change in spectral index, and all of which are almost certainly regular radio-loud A G N . Four sources were partially resolved, showing some level of vari-ability in both structure and flux density as well as changes in spectral index. The evidence for short term structural changes suggests these may be galactic jet sources. It would be desirable to confirm the structural variations with higher resolution observa-tions. Twelve sources were completely unresolved, five of which exhibit some variability and eight of which exhibit a notable change in spectral index. From the APS results one of these unresolved sources appears likely to be stellar. The moderate to low levels of flux density variation seen in the partially resolved and specifically the unresolved sources may be attributable, at least in part, to RISS. Although the unresolved sources are most likely to be extremely distant blazars, with the intrinsic core variability enhanced by rel-ativistic doppler effects, if they are indeed extragalactic point-like sources, as opposed to flaring radio stars, they will be susceptible to RISS, and RISS may account for a fraction of the observed variability. One of the 24 short term variable sources studied did not Chapter 6. Results and Conclusion 83 appear at all in the observed V L A image field. To interpret the correlation of variability results from this V L A study with the mea-sured GB6 short term variability, one must consider effects of statistical sampling. Ran-dom time sampling of a flux density distribution will usually result in an underestimation of the true variability level, especially for small samples, as in the V L A study. However, due to the selection process, the observed GB6 variability levels, of the 24 chosen sources, are biased towards true variability levels and levels artificially enhanced by chance as a consequence of flux density uncertainties. Even in the context of statistical sampling, the V L A determined low variability level may still perhaps be inconsistent with the higher GB6 short term variability, particularly for the one-sided and two-sided A G N ; a Monte Carlo simulation could settle this question. It is difficult to speculate as to the reason for the discrepancy, if in fact it exists, but the high Q values, especially for the mentioned sources, may be indicative of rare core flaring events, or perhaps the uncertainties in the daily flux density measurements provided [2] are underestimated and may be affected by sporadic, unaccounted noise. A summary of averaged V L A measured parameters for observed sources is given in table 6.8. The V L A measured source flux densities, as projected to longer wavelengths using V L A spectral indices, for the majority of sources, are consistent with GB6 long term epoch flux density measurements. Both epoch V L A flux density measurements, for three sources, J0048+684, J0049+343, and J0502+346, fall just above maximum GB6 daily flux data, and two sources, J0856+717 and J1700+685 lie just below GB6 daily flux minima. The observed GB6 daily flux variation levels in all five of these sources convincingly suggest the above V L A flux density data are plausible, and are not considered a discrepancy. The structural ambiguity of the partially and unresolved sources may be removed with Chapter 6. Results and Conclusion 84 V L A A configuration snapshots, with the slightly higher resolution perhaps making iden-tification possible. Of the unresolved sources, three are intriguing based on observed vari-ability, with J0251+562 being significantly variable at K band, J0611+723 significantly variable at U band and moderately variable at X band, and J0502+346 being significantly variable at both X and U band. The observed level of variability in these sources is most likely dominantly intrinsic and should be monitored with multi-epoch V L A flux density measurements, particularly J0502+346, which is the most interesting unresolved source. Three partially resolved sources J1700+865, J2145+187 and J2115+367 exhibit some structural variation with both J1700+685 and J2115+367 also varying in flux density at X band. A l l three of these partially resolved sources warrant further attention with high resolution multi-epoch observations using the V L A in A configuration or V L B A / V L B I . After further high resolution radio imaging, perhaps optical wavelength observations and spectral analysis may be useful to provide distance estimates and assist classification. As a whole the adopted source selection process and observation strategies are be-lieved to be a success, but with the benefit of hindsight and daily flux data currently being extracted for the entire GB6 catalog, some improvements are possible for future short term variability studies. From the complete set of GB6 daily flux measurements one may be able to determine, for each source, not only a characteristic short term vari-ability index, but also a characteristic, or most significant time scale, from the time scale distribution of variability indices. Due to time constraints, including those imposed by the V L A proposal deadlines, and a limited subset of short term variability information, improved source selection criteria, based on statistical analysis of above characteristic parameters, were not explored. A n augmented sample of short term variables would allow concentrated focus on sources exhibiting significant short term variability index, at a high confidence level, during both epochs. Furthermore, with the eventual completion of the NVSS, FIRST, APS, and other databases, the information provided should be Chapter 6. Results and Conclusion incorporated into the short term variable selection process. Bibliography Gregory, P . C , Scott, W . K . , Douglas, K . ,& Condon, J.J., "The GB6 Catalog of Radio Sources", Astrophys-ical Journal Supplement 1 0 3 : 427 (1996) Scott, Will iam K. , "Compact Radio Source Variability at Centimeter Wavelengths", Ph.D. Thesis, University of British Columbia (1996) Mirabel, I.F, &, Rodriguez, L .F "Superluminal Motions in our Galaxy", Invited Review at the 17th Texas Sym-posium on Relativistic Astrophysics; Munich, Germany (Decenber 1994) Hjellming, R . M . , & Rupen, M.P. "Episodic ejection of relativistic jets by the X-ray transient G R O J1655-40", Nature 3 7 5 : 464-468 (June 1995) Vermeulen, R.C. , Schlizzi, R.T. , Spencer, R .E , Romney, J.D., & Fejes, I. "A series of V L B I images of SS433 dur-ing the outbursts in May/June 1987", Astronomy and Astrophysics 2 0 7 : 177-188 (1993) Rickett, B . J . "Refractive Interstelar Scintillation of Radio Sources", The Astrophysical Journal307: 564-574 (1986) Rickett, B . J . , Quirrenbach, A. , Wegner, R., Krichbaum, T.P., & Witzel, A . "Interstellar Scintillation of Radio Source 0917+624", Astronomy and Astrophysics 2 9 3 : 479-492(1995) Perley, R . A . "Very Large Array Observational Status Summary", N R A O Publication (1996) Staff of N R A O ; Hjellming R . M . (ed.) "An introduction to the NRAO Very Large Array, Edition 2.0", N R A O Publication (1992) Perley, R . A . & Taylor, G.B. "The VLA Calibrator Man-ual", N R A O Publication (1996) 86 87 Perley, R .A. , Schwab, F.R. & Bridle, A . H . (eds.) "Syn-thesis Imaging" Course Notes from an N R A O Summer School Held in Socorro, New Mexico, Aug 5-9, 1985; N R A O Publication (1986) Verschuur, G.L. & Kellermann, K.I . (eds.) "Galactic and Extragalactic Radio Astronomy", Springer-Veriag (1974) Hjellming, R . M . "Chapter 7: Radio Stars" (159-178) Verschuur, G .L . & Kellermann, K.I . (eds.) "Galactic and Extragalactic Radio Astronomy", Springer-Veriag (1974) Kellermann, K. I . "Chapter 12: Radio Galaxies and Quasars" (320-352) Roland, H.S. &; Pelletier, G. (eds.) "Extragalactic Radio Sources - From Beams to Jets", Cambridge University Press (1991) Zensus, J .A. & Pearson, T .J . (eds.) "Superluminal Radio Sources", Cambridge University Press (1986) Hey, J.S. "The Radio Universe, 3rd Edition", Pergamon Press (1983) Davis, R.J . , & Booth, R.S. (eds.) "Sub-arcsecond Radio Astronomy", Cambridge University Press (1992) Urry, C M . & Padovani, P. "Unification Schemes for Radio-Loud Active Galactic Nuclei", Publications of the Astronomical Society of the Pacific, Invited Review Pa-per, 107: 803-845, (1995) Bridle, A . H . , Clarke, D.A. , Burns, J.O., Perley, R .A. , & Norman, M . L . "Origin of the structures and polarization in the classical double 3C219", The Astronomical Jour-nal, 3 8 5 : 173-187 (1992) Zeilik, M . , & Gaustad, J., "Astronomy: The Cosmic Per-spective, 2nd Edition", John Wiley & Sons Publishers (1983) Kaufmann, Will iam J . I l l , & Comins, Neil F. , "Discov-ering the Universe, J^th Edition", W. H . Freeman and Company Publishers (1996) Appendix A Short Term Variable Tables A . l Short Term Variable Positions N A M E J2000 Position ± Catalog Galactic J0003+249 0: 3:18.4 +24:59:40 12 GB6 -36.6 109.3 J0005+544 0: 5: 5.8 +54:28:36 9 GB6 -7.8 116.2 J0019+734 0:19:45.2 +73:27:27 6 GB6 10.7 120.6 J0036+185 0:36:59.34 +18:32: 3.3 0.4 NVSS -44.2 118.2 J0039+411 0:39:54.9 +41:11:41 19 GB6 -21.6 120.6 J0042+544 0:42: 5.5 +54:25:48 11 GB6 -8.4 121.6 J0047+569 0:47: 0.0 +56:57:51 8 GB6 -5.9 122.3 J0048+684 0:48:35.4 +68:26:29 9 GB6 5.6 122.7 J0049+343 0:49:45.7 +34:22:30 12 GB6 -28.5 122.5 J0120+265 1:20:57.3 +26:31:49 18 GB6 -35.9 131.1 J0121+118 1:21:40.7 +11:49:42 11 GB6 -50.4 134.6 J0128+490 1:28: 8.1 +49: 1:13 9 GB6 -13.4 129.1 J0202+397 2: 2: 1.6 +39:43:16 11 GB6 -21.2 137.4 J0228+673 2:28:50.2 +67:20:57 7 GB6 6.2 132.1 J0235+622 2:35:21.7 +62:16:17 11 GB6 1.8 134.7 J0249+511 2:49:22.7 +51: 8:16 10 GB6 -7.5 141.1 J0249+221 2:49: 9.41 +22: 8:12.3 0.4 NVSS -33.1 155.8 J0251+562 2:51:54.53 +56:16:19.1 0.4 NVSS -2.8 139.1 J0259+516 2:59:38.23 +51:38:14.5 0.4 NVSS -6.3 142.3 J0258+056 2:58:50.51 + 5:41: 7.3 0.4 NVSS -45.0 170.9 J0302+535 3: 2:23.4 +53:31:52 9 GB6 -4.5 141.7 J0304+683 3: 4:22.4 +68:21:46 7 GB6 8.6 134.7 J0310+391 3:10:25.0 +39:10:50 12 GB6 -16.2 150.3 J0310+382 3:10:49.6 +38:14:51 11 GB6 -16.9 150.9 J0323+462 3:23:57.2 +46:14:20 11 GB6 -8.9 148.5 J0325+349 3:25:20.3 +34:57:18 15 GB6 -18.0 155.4 88 Appendix A. Short Term Variable Tables 89 N A M E J2000 Position ± Catalog Galactic J0325+224 3:25:36.81 +22:24: 1.0 0.4 NVSS -28.0 163.7 J0326+287 3:26:34.9 +28:42:51 12 GB6 -22.9 159.5 J0332+545 3:32:59.25 +54:34:44.1 0.5 NVSS -1.2 145.0 J0340+540 3:40: 6.53 +54: 5:37.7 0.5 NVSS -1.0 146.1 J0350+516 3:50:24.98 +51:38:38.9 0.4 NVSS -2.0 148.8 J0357+418 3:57:41.41 +41:48:46.1 0.4 NVSS -8.7 156.1 J0411+087 4:11:33.84 + 8:43:12.0 0.4 NVSS -29.7 183.7 J0424+006 4:24:46.80 + 0:36: 6.6 0.4 NVSS -31.8 193.6 J0430+169 4:30:22.30 +16:55: 5.3 0.6 NVSS -21.0 179.8 J0431+206 4:31: 3.75 +20:37:34.0 0.4 NVSS -18.6 176.8 J0440+146 4:40:21.09 +14:37:57.1 0.4 NVSS -20.5 183.2 J0444+251 4:44:58.12 +25: 9:36.2 0.5 NVSS -13.2 175.3 J0445+072 4:45: 1.40 + 7:15:53.5 0.4 NVSS -23.9 190.5 J0449+635 4:49:23.34 +63:32: 8.8 0.4 NVSS 11.9 146.0 J0502+388 5: 2:32.46 +38:49:54.9 0.5 NVSS -1.8 166.8 J0502+346 5: 2:29.88 +34:36:34.7 0.4 NVSS -4.4 170.2 J0518+331 5:18: 5.23 +33: 6:12.5 0.4 NVSS -2.7 173.3 J0530+550 5:30:16.73 +55: 2:48.5 0.4 NVSS 11.4 156.2 J0532+562 5:32:59.47 +56:12:24.8 0.4 NVSS 12.3 155.4 J0534+089 5:34: 8.40 + 8:54:49.9 0.6 NVSS -12.7 195.8 J0547+111 5:47:46.66 +11: 7:36.2 0.4 NVSS -8.7 195.6 J0607+712 6: 7:19.2 +71:16: 7 7 GB6 22.2 142.8 J0606+146 6: 6:21.07 +14:36:17.3 0.4 NVSS -3.1 194.8 J0611+723 6:11: 9.20 +72:18:16.3 0.5 NVSS 22.8 141.9 J0615+450 6:15:18.04 +45: 1:59.5 0.4 NVSS 12.9 168.7 J0629+044 6:29:56.23 + 4:26:32.8 0.4 NVSS -2.7 206.5 J0658+193 6:58:36.94 +19:19:15.9 0.7 NVSS 10.2 196.3 J0714+146 7:14: 4.67 +14:36:20.8 0.4 NVSS 11.5 202.3 J0716+367 7:16:37.10 +36:42:18.0 0.5 NVSS 20.5 181.2 J0722+181 7:22: 5.60 +18:11:17.8 0.6 NVSS 14.8 199.8 J0731+673 7:31:25.52 +67:18:47.3. 0.5 NVSS 28.7 148.6 Appendix A. Short Term Variable Tables N A M E J2000 Position ± Catalog Galactic J0737+645 7:37:58.95 +64:30:43.3 0.4 NVSS 29.3 151.8 J0738+177 7:38: 7.35 +17:42:19.5 0.4 NVSS 18.1 201.8 J0751+272 7:51:41.46 +27:16:31.7 0.4 NVSS 24.5 193.5 J0815+619 8:15:39.26 +61:54:27.9 0.4 NVSS 33.6 154.8 J0839+033 8:39:49.16 + 3:19:54.2 0.4 NVSS 25.5 222.9 J0849+098 8:49:41.11 + 9:49:27.0 0.4 NVSS 30.7 217.6 J0856+717 8:56:54.60 +71:46:24.9 0.4 NVSS 35.3 142.0 J0903+636 9: 3:37.94 +63:38:11.8 0.4 NVSS 38.6 151.4 J0921+569 9:21: 7.43 +56:56:58.8 0.6 NVSS 42.6 159.0 J0927+572 9:27: 6.10 +57:17:44.7 0.4 NVSS 43.3 158.2 J0939+421 9:39: 6.69 +42: 7:18.3 0.4 NVSS 48.3 179.0 J0943+435 9:43: 9.05 +43:35:20.3 0.4 NVSS 48.9 176.7 J0944+520 9:44:52.13 +52: 2:33.8 0.4 NVSS 47.3 164.2 J0957+553 9:57:38.14 +55:22:57.3 0.4 NVSS 47.9 158.6 J0958+655 9:58:47.18 +65:33:54.2 0.4 NVSS 43.1 145.7 J1001+139 10: 1:40.1 +13:59:11 23 GB6 48.4 222.6 J1015+558 10:15:44.22 +55:51: 0.2 0.4 NVSS 50.0 156.2 J1016+052 10:16: 2.6 + 5:13: 4 12 GB6 47.0 236.5 J1019+633 10:19:50.86 +63:20: 2.3 0.4 NVSS 46.3 146.4 J1031+746 10:31:22.31 +74:41:58.3 0.4 NVSS 39.2 134.2 J1030+515 10:30:35.15 +51:32:32.8 0.4 NVSS 54.0 160.6 J1037+571 10:37:44.24 +57:11:56.3 0.4 NVSS 51.8 151.8 J1048+717 10:48:27.55 +71:43:35.1 0.4 NVSS 42.3 135.4 J1103+720 11: 3:48.35 +72: 2:24.1 0.6 NVSS 42.7 133.9 J1106+282 11: 6: 7.22 +28:12:47.3 0.4 NVSS 66.7 204.1 J1106+172 11: 6:26.3 +17:13:30 12 GB6 63.8 229.7 J1112+350 11:12:33.18 +35: 3:39.6 0.5 NVSS 67.5 186.2 J1115+649 11:15:39.16 +64:59:31.6 0.4 NVSS 49.2 138.1 J1120+126 11:20:31.5 +12:41: 9 12 GB6 64.3 242.6 J1125+399 11:25:25.52 +39:59: 4.6 0.5 NVSS 68.0 171.6 J1127+568 11:27:40.16 +56:50:15.5 0.4 NVSS 56.8 143.8 Appendix A. Short Term Variable Tables N A M E J2000 Position ± Catalog Galactic J1153+251 11:53:18.09 +25: 9: 4.8 0.4 NVSS 76.8 218.3 J1157+077 11:57:12.9 + 7:43:35 23 GB6 66.7 266.9 J1205+008 12: 5:47.9 + 0:53:26 15 GB6 61.6 278.4 J1206+527 12: 6:23.5 +52:42:45 11 GB6 63.1 138.1 J1221+083 12:21:31.1 + 8:21:30 28 GB6 69.9 280.9 J1222+042 12:22:21.4 + 4:13:16 12 GB6 66.1 284.8 J1229+553 12:29: 9.22 +55:22:30.4 0.4 NVSS 61.5 129.6 J1236+393 12:36:51.52 +39:20:27.0 0.5 NVSS 77.4 136.0 J1238+212 12:38:17.3 +21:14:31 16 GB6 83.4 275.2 J1239+342 12:39:54.08 +34:15:29.4 0.5 NVSS 82.5 141.4 J1243+398 12:43:18.81 +39:51:17.1 0.5 NVSS 77.2 129.9 J1243+732 12:43:10.28 +73:16: 0.8 0.4 NVSS 43.9 123.8 J1248+154 12:48:38.8 +15:29:40 21 GB6 78.3 299.6 J1250+110 12:50:59.6 +11: 4: 9 18 GB6 73.9 302.5 J1256+350 12:56:11.25 +35: 2:18.8 0.4 NVSS 82.0 116.0 J1300+234 13: 0:17.9 +23:28:26 12 GB6 85.8 332.1 J1303+513 13: 3: 1.29 +51:19:47.7 0.5 NVSS 65.7 118.5 J1307+064 13: 7: 4.0 + 6:27:54 13 GB6 69.0 313.8 J1309+524 13: 9: 7.87 +52:24:36.8 0.5 NVSS 64.5 116.6 J1318+044 13:18:29.2 + 4:29:55 13 GB6 66.5 320.0 J1325+350 13:25:44.42 +35: 4:46.8 0.5 NVSS 79.2 82.4 J1326+445 13:26:36.95 +44:34:58.9 0.4 NVSS 71.2 103.2 J1350+320 13:50:44.3 +32: 5: 9 23 GB6 76.2 57.5 J1355+304 13:55:41.05 +30:24:11.4 0.4 NVSS 75.6 49.8 J1356+405 13:56:43.50 +40:35: 4.5 0.4 NVSS 71.0 82.1 J1403+637 14: 3:31.41 +63:42:53.0 0.4 NVSS 51.6 110.2 J1419+383 14:19:46.53 +38:21:48.7 0.5 NVSS 68.4 69.8 J1428+043 14:28:16.3 + 4:19:41 16 GB6 57.5 352.6 J1434+420 14:34: 5.62 +42: 3:15.9 0.4 NVSS 64.3 75.1 J1437+381 14:37:33.36 +38: 7:44.9 0.5 NVSS 65.2 66.0 J1437+300 14:37:58.63 +30: 2: 6.8 0.5 NVSS 66.5 46.3 Appendix A. Short Term Variable Tables N A M E J2000 Position ± Catalog Galactic J1438+367 14:38:13.64 +36:44:50.6 0.5 NVSS 65.5 62.7 J1442+287 14:42:43.18 +28:46:38.7 0.5 NVSS 65.4 43.3 J1508+414 15: 8:46.57 +41:27:57.1 0.4 NVSS 58.5 68.9 J1520+745 15:20:43.8 +74:35:43 14 GB6 38.9 111.0 J1549+214 15:49:48.2 +21:25:44 11 GB6 49.2 34.9 J1554+028 15:54:48.6 + 2:52:19 23 GB6 39.9 12.1 J1603+110 16: 3:42.7 +11: 5:46 11 GB6 42.2 23.0 J1606+133 16: 6:54.5 +13:19:33 13 GB6 42.4 26.2 J1608+104 16: 8:46.3 +10:29: 5 11 GB6 40.8 23.0 J1609+284 16: 9:40.20 +28:28:45.3 0.6 NVSS 46.5 46.8 J1612+204 16:12:59.7 +20:28:34 17 GB6 43.7 36.0 J1618+489 16:18:26.47 +48:59:39.3 0.5 NVSS 44.9 76.3 J1624+568 16:24:33.0 +56:52:38 9 GB6 42.3 86.6 J1631+108 16:31:19.1 +10:52: 3 13 GB6 36.0 26.6 J1630+741 16:30:26.52 +74: 9:33.1 0.4 NVSS 35.4 107.1 J1649+681 16:49:36.7 +68: 6:47 16 GB6 36.2 99.5 J1656+533 16:56:41.2 +53:21:51 9 GB6 38.4 81.0 J1657+481 16:57:46.91 +48: 8:32.6 0.4 NVSS 38.5 74.4 J1702+079 17: 2:28.7 + 7:57: 4 12 GB6 27.8 27.5 J1700+685 17: 0: 9.24 +68:30: 6.5 0.4 NVSS 35.2 99.6 J1711+541 17:11:41.2 +54:11:50 9 GB6 36.1 81.9 J1716+689 17:16: 8.2 +68:56:10 7 GB6 33.7 99.7 J1716+686 17:16:13.91 +68:36:38.2 0.4 NVSS 33.8 99.3 J1717+743 17:17:38.68 +74:18:39.2 0.4 NVSS 32.3 105.9 J1722+610 17:22:40.02 +61: 5:59.9 0.4 NVSS 34.2 90.2 J1732+009 17:32:24.4 + 0:59:43 16 GB6 18.0 24.5 J1740+438 17:40:48.0 +43:48:25 10 GB6 30.7 69.8 J1740+521 17:40:36.5 +52:11:47 9 GB6 31.7 79.6 J1745+670 17:45:54.38 +67: 3:49.0 0.4 NVSS 31.2 97.0 J1756+453 17:56:24.9 +45:23:28 13 GB6 28.2 72.2 J1759+287 17:59:15.2 +28:47:50 12 GB6 23.3 54.6 Appendix A. Short Term Variable Tables N A M E J2000 Position ± Catalog Galactic J1803+431 18: 3:14.1 +43: 6:20 21 GB6 26.6 70.0 J1808+451 18: 8: 2.1 +45:11:42 36 GB6 26.2 72.5 J1810+016 18:10: 2.2 + 1:36:48 14 GB6 9.9 29.6 J1814+228 18:14: 1.5 +22:49: 3 24 GB6 18.1 49.9 J1849+670 18:49:15.87 +67: 5:40.8 0.4 NVSS 25.0 97.5 J1851+499 18:51:21.0 +49:59:14 14 GB6 20.5 79.6 J1852+489 18:52:29.4 +48:55:49 9 GB6 19.9 78.6 J1856+061 18:56:31.4 + 6:10:13 12 GB6 1.7 39.0 J1924+286 19:24:14.7 +28:38: 0 12 GB6 6.1 62.0 J1956+635 19:56:25.8 +63:32:42 8 GB6 17.3 96.3 J2053+530 20:53:12.6 +53: 1:38 9 GB6 5.3 91.5 J2055+613 20:55:39.4 +61:22: 1 8 GB6 10.4 98.3 J2102+470 21: 2:17.7 +47: 2: 6 9 GB6 0.3 87.9 J2115+367 21:15:39.5 +36:45:56 11 GB6 -8.4 82.0 J2140+107 21:40: 5.3 +10:47:35 18 GB6 -30.1 65.6 J2145+187 21:45:14.35 +18:45:19.8 0.4 NVSS -25.7 73.2 J2147+153 21:47:24.9 +15:20:52 11 GB6 -28.4 70.9 J2152+653 21:52:28.0 +65:20:35 9 GB6 8.7 105.7 J2201+248 22: 1:12.9 +24:51:17 15 GB6 -23.8 80.8 J2201+508 22: 1:43.4 +50:48:51 9 GB6 -3.5 97.6 J2202+292 22: 2: 5.3 +29:14:53 12 GB6 -20.6 84.1 J2208+615 22: 8:10.2 +61:32:55 11 GB6 4.6 104.7 J2240+515 22:40:19.1 +51:33: 8 10 GB6 -6.2 103.1 J2251+440 22:51:58.4 +44: 3:38 11 GB6 -13.7 101.3 J2258+496 22:58:26.0 +49:37:55 11 GB6 -9.2 104.8 J2327+096 23:27:33.7 + 9:40: 9 11 GB6 -48.0 91.1 J2350+111 23:50: 1.8 +11: 6:28 12 GB6 -49.0 99.6 J0002+749 0: 2:33.4 +74:59:45 8 GB6 12.4 119.7 Appendix A. Short Term Variable Tables A . 2 S h o r t T e r m V a r i a b l e F l u x R e l a t e d I n f o r m a t i o n N A M E ^ 8 6 Far F6 F20 a -logQs6 -logQ.87 J0003+249 140 ± 8 59 ± 6 98 ± 9 1.2 3.8 8.0 J0005+544 184 ± 8 259 ± 10 231 ± 21 2.1 0.3 5.7 J0019+734 1377 ± 35 1712 ± 44 1583 ± 1 4 1 2.7 4.2 6.0 J0036+185 52 ± 6 147 ± 9 126 ± 12 123 ± 4 0.0 0.3 3.6 9.0 J0039+411 36 ± 10 38 ± 12 34 ± 5 4.0 0.8 J0042+544 58 ± 5 98 ± 6 82 ± 8 0.7 2.3 5.3 J0047+569 212 ± 9 302 ± 11 273 ± 24 3.0 2.1 6.3 J0048+684 49 ± 4 102 ± 5 81 ± 8 5.9 3.3 7.5 J0049+343 87 ± 6 141 ± 8 111 ± 10 5.9 1.6 5.4 J0120+265 54 ± 11 44 ± 17 41 ± 5 0.1 3.0 J0121+118 1462 ± 68 967 ± 45 1126 ± 1 0 0 4.7 2.2 6.0 J0128+490 594 ± 23 288 ± 12 408 ± 36 1.0 4.1 11.7 J0202+397 79 ± 6 131 ± 7 107 ± 10 2.5 0.9 5.5 J0228+673 1120 ± 33 1767 ± 52 1511 ± 1 3 4 0.2 3.7 10.5 J0235+622 48 ± 4 87 ± 5 68 ± 7 0.4 4.0 5.6 J0249+511 130 ± 7 82 ± 6 104 ± 10 0.4 3.8 5.5 J0249+221 115 ± 7 173 ± 9 149 ± 14 421 ± 14 0.9 8.2 0.4 4.8 J0251+562 352 ± 13 252 ± 10 310 ± 27 196 ± 6 -0.4 4.2 2.0 6.1 J0259+516 119 ± 6 61 ± 5 96 ± 9 89 ± 3 -0.1 1.2 11.7 7.1 J0258+056 139 ± 10 241 ± 13 213 ± 19 150 ± 5 -0.3 3.7 0.4 6.2 J0302+535 220 ± 9 358 ± 14 280 ± 25 2.4 1.4 8.3 J0304+683 942 ± 27 1491 ± 43 1242 ± 1 1 0 1.2 3.1 10.8 J0310+391 64 ± 6 109 ± 7 90 ± 9 0.3 2.9 5.2 J0310+382 356 ± 16 760 ± 32 628 ± 56 20.5 1.6 11.3 J0323+462 72 ± 5 133 ± 7 98 ± 9 3.2 0.2 6.8 J0325+349 35 ± 5 79 ± 6 55 ± 6 3.8 0.4 5.5 J0325+224 995 ± 45 711 ± 33 817 ± 72 532 ± 17 -0.4 3.3 7.9 5.1 J0326+287 192 ± 10 41 ± 5 116 ± 11 50.5 8.1 13.4 J0332+545 50 ± 5 4 ± 5 26 ± 4 151 ± 5 1.5 4.4 3.7 7.0 J0340+540 67 ± 5 110 ± 6 90 ± 8 126 ± 4 0.3 2.3 1.4 5.4 J0350+516 146 ± 7 204 ± 9 175 ± 16 123 ± 4 -0.3 0.6 2.0 5.1 J0357+418 71 ± 6 131 ± 7 118 ± 11 430 ± 14 1.1 5.7 1.7 6.6 J0411+087 56 ± 7 198 ± 11 137 ± 13 112 ± 4 -0.2 2.2 3.3 10.6 J0424+006 712 ± 34 1118 ± 53 879 ± 78 512 ± 17 -0.4 0.2 2.1 6.4 J0430+169 85 ± 7 143 ± 9 108 ± 10 42 ± 1 -0.8 13.5 1.7 5.2 Appendix A. Short Term Variable Tables N A M E Fae ^ 8 7 Fe ^ 2 0 Q -logQae - l o g Q & 7 J0431+206 1971 ± 90 2811 ± 1 2 8 2414 ± 2 1 5 3822 ± 1 2 0 0.4 0.1 10.5 5.4 J0440+146 175 ± 10 347 ± 17 264 ± 24 222 ± 7 -0.1 0.1 2.1 8.7 J0444+251 22 ± 19 37 ± 10 29 ± 4 56 ± 2 0.5 0.2 6.2 J0445+072 505 ± 25 271 ± 14 371 ± 33 365 ± 12 0.0 5.3 0.7 8.2 J0449+635 399 ± 13 606 ± 20 519 ± 46 434 ± 14 -0.1 2.7 0.1 8.8 J0502+388 172 ± 9 289 ± 13 239 ± 21 60 ± 2 -1.1 2.5 8.9 7.5 J0502+346 70 ± 6 114 ± 7 106 ± 10 178 ± 6 0.4 3.3 6.8 4.8 J0518+331 203 ± 10 292 ± 14 256 ± 23 353 ± 12 0.3 3.4 0.6 5.3 J0530+550 183 ± 8 244 ± 10 220 ± 20 520 ± 16 0.7 2.3 1.5 4.9 J0532+562 89 ± 5 130 ± 6 113 ± 10 111 ± 4 0.0 7.4 2.5 5.0 J0534+089 37 ± 7 97 ± 8 74 ± 8 32 ± 1 -0.7 0.2 2.4 5.8 J0547+111 37 ± 10 39 ± 12 38 ± 6 80 ± 3 0.6 0.2 2.3 J0607+712 175 ± 6 228 ± 8 203 ± 18 5.5 1.2 5.4 J0606+146 20 ± 9 45 ± 9 45 ± 6 111 ± 4 0.7 2.1 3.9 J0611+723 44 ± 4 116 ± 6 87 ± 8 60 ± 2 -0.3 6.3 3.3 10.1 J0615+450 59 ± 5 18 ± 5 20 ± 4 62 ± 2 0.9 0.0 5.6 5.8 J0629+044 58 ± 14 114 ± 17 89 ± 9 92 ± 3 0.0 0.1 2.0 J0658+193 32 ± 11 53 ± 11 34 ± 5 30 ± 1 -0.1 1.1 2.1 J0714+146 520 ± 25 790 ± 37 679 ± 60 1999 ± 66 0.9 0.6 2.0 6.1 J0716+367 92 ± 6 150 ± 8 140 ± 13 304 ± 10 0.6 3.2 0.4 5.7 J0722+181 24 ± 6 39 ± 13 41 ± 5 44 ± 1 0.1 6.0 0.5 J0731+673 292 ± 9 171 ± 7 226 ± 20 58 ± 2 -1.1 3.4 0.2 10.4 J0737+645 301 ± 10 229 ± 8 251 ± 22 418 ± 13 0.4 2.5 1.4 5.4 J0738+177 1530 ± 70 2166 ± 1 0 0 1812 ± 1 6 1 2289 ± 72 0.2 31.4 1.9 5.2 J0751+272 148 ± 8 214 ± 11 193 ± 17 605 ± 19 0.9 0.5 2.6 4.9 J0815+619 47 ± 4 81 ± 5 61 ± 6 108 ± 3 0.5 1.4 2.6 4.9 J0839+033 776 ± 37 510 ± 25 673 ± 60 669 ± 20 0.0 1.2 2.0 5.9 J0849+098 252 ± 13 157 ± 10 204 ± 18 295 ± 10 0.3 0.3 2.2 5.8 J0856+717 144 ± 6 208 ± 7 174 ± 16 64 ± 2 -0.8 2.8 4.6 7.0 J0903+636 17 ± 5 33 ± 5 25 ± 4 50 ± 2 0.6 6.2 7.1 J0921+569 39 ± 5 72 ± 5 53 ± 6 37 ± 1 -0.3 0.4 5.5 4.8 J0927+572 98 ± 5 147 ± 7 123 ± 11 91 ± 3 -0.3 0.8 2.5 5.7 J0939+421 32 ± 10 32 ± 11 24 ± 4 90 ± 3 1.1 0.5 3.6 J0943+435 20 ± 8 25 ± 9 34 ± 5 76 ± 3 0.7 0.6 3.5 J0944+520 463 ± 18 345 ± 13 391 ± 35 624 ± 20 0.4 0.3 31.6 5.3 J0957+553 1704 ± 60 2270 ± 80 2015 ± 1 7 9 3123 ± 98 0.4 9.0 5.4 5.6 Appendix A. Short Term Variable Tables N A M E Fa6 F87 F6 F20 a -logQse -logQs7 Va J0958+655 908 ± 28 1417 ± 43 1125 ± 1 0 0 740 ± 23 -0.3 14.6 0.5 10.0 J1001+139 34 ± 11 59 ± 11 34 ± 5 4.0 0.3 J1015+558 49 ± 5 89 ± 6 62 ± 6 138 ± 5 0.7 0.3 4.9 5.5 J1016+052 496 ± 24 745 ± 36 593 ± 53 2.6 0.1 5.8 J1019+633 . 205 ± 8 271 ± 10 237 ± 21 109 ± 3 -0.6 3.3 0.1 5.3 J1031+746 273 ± 8 202 ± 7 250 ± 22 199 ± 6 -0.2 4.1 0.7 6.8 J1030+515 106 ± 6 150 ± 7 128 ± 12 186 ± 6 0.3 3.1 0.5 4.7 J1037+571 180 ± 8 88 ± 5 126 ± 11 72 ± 2 -0.5 0.4 2.0 9.9 J1048+717 1460 ± 38 2410 ± 63 1900 ± 1 6 9 751 ± 24 -0.8 0.2 4.6 12.8 J1103+720 31 ± 4 64 ± 5 44 ± 5 37 ± 1 -0.1 1.1 3.7 4.9 J1106+282 537 ± 24 274 ± 13 369 ± 33 225 ± 7 -0.4 6.0 1.5 9.6 J1106+172 123 ± 8 207 ± 11 152 ± 14 1.4 3.0 6.2 J1112+350 76 ± 6 122 ± 7 101 ± 9 135 ± 4 0.2 1.8 3.1 4.9 J1115+649 19 ± 10 57 ± 10 31 ± 4 101 ± 3 1.0 1.6 3.1 J1120+126 113 ± 8 176 ± 10 151 ± 14 2.5 0.1 4.9 J1125+399 56 ± 5 99 ± 6 70 ± 7 182 ± 6 0.8 3.5 0.3 5.2 J1127+568 370 ± 14 597 ± 21 448 ± 40 484 ± 16 0.1 0.1 2.4 9.0 J1153+251 91 ± 7 38 ± 5 65 ± 7 72 ± 2 0.1 0.4 3.0 6.2 J1157+077 17 ± 8 67 ± 11 40 ± 6 2.6 2.3 J1205+008 135 ± 10 218 ± 13 141 ± 15 4.5 0.0 5.0 J1206+527 114 ± 6 70 ± 5 85 ± 8 0.3 5.0 5.4 J1221+083 51 ± 7 120 ± 9 58 ± 8 0.9 3.4 6.2 J1222+042 1328 ± 63 934 ± 44 1351 ± 1 2 0 15.9 8.7 5.1 J1229+553 68 ± 5 127 ± 6 106 ± 10 54 ± 2 -0.6 1.5 4.3 7.2 J1236+393 284 ± 13 193 ± 9 246 ± 22 352 ± 11 0.3 0.1 4.2 5.8 J1238+212 19 ± 5 60 ± 6 48 ± 6 3.1 1.4 5.0 J1239+342 38 ± 5 81 ± 6 59 ± 6 85 ± 3 0.3 3.8 1.1 5.4 J1243+398 36 ± 5 71 ± 6 58 ± 6 52 ± 2 -0.1 0.1 6.9 4.7 J1243+732 276 ± 8 345 ± 10 312 ± 27 299 ± 10 0.0 2.5 6.1 5.4 J1248+154 15 ± 8 . 31 ± 13 38 ± 5 1.5 3.3 J1250+110 88 ± 7 32 ± 6 73 ± 9 0.1 3.2 5.8 J1256+350 61 ± 6 117 ± 7 92 ± 9 300 ± 10 1.0 1.1 2.0 6.2 J1300+234 67 ± 21 107 ± 1 0 0 103 ± 10 0.5 4.6 J1303+513 77 ± 5 125 ± 7 90 ± 8 169 ± 5 0.5 7.3 0.5 5.6 J1307+064 151 ± 10 263 ± 14 146 ± 14 11.5 0.9 6.5 J1309+524 17 ± 8 26 ± 10 27 ± 4 62 ± 2 0.7 2.0 1.5 Appendix A. Short Term Variable Tables N A M E ^ 8 6 F 8 7 F6 F20 OL -logQ 86 -logQs7 J1318+044 238 ± 13 122 ± 9 222 ± 21 0.0 3.8 7.2 J1325+350 48 ± 11 29 ± 9 29 + 4 42 ± 1 0.3 0.5 5.1 J1326+445 105 ± 6 162 ± 8 140 ± 13 182 ± 6 0.2 0.6 3.5 5.7 J1350+320 2 ± 5 44 + 5 29 ± 4 0.1 5.9 5.7 J1355+304 84 ± 6 135 ± 8 103 ± 10 143 ± 5 0.3 14.5 0.7 5.1 J1356+405 28 ± 10 54 ± 12 24 ± 4 74 ± 2 0.9 0.2 4.2 J1403+637 373 ± 12 491 ± 16 433 ± 38 916 ± 28 0.6 0.4 2.4 5.9 J1419+383 381 ± 17 871 ± 37 651 ± 58 621 ± 20 0.0 2.4 1.9 12.2 J1428+043 115 ± 9 190 ± 11 115 ± 12 1.3 2.3 5.2 J1434+420 177 ± 9 353 ± 15 280 ± 25 313 ± 10 0.1 1.6 2.3 10.2 J1437+381 55 ± 5 100 ± 6 83 + 8 218 ± 7 0.8 2.1 0.4 5.4 J1437+300 73 ± 6 132 ± 8 99 ± 9 60 ± 2 -0.4 2.4 0.2 6.0 J1438+367 62 ± 6 102 ± 6 75 + 7 58 ± 2 -0.2 1.4 2.5 4-7 J1442+287 3 ± 8 30 ± 10 32 + 5 69 ± 2 0.6 0.1 2.3 J1508+414 78 + 6 130 ± 7 117 ± 11 415 ± 14 1.1 1.9 2.1 5.6 J1520+745 56 ± 11 69 ± 13 47 + 5 5.2 0.6 J1549+214 546 ± 25 765 ± 35 636 ± 56 0.6 4.2 5.1 J1554+028 37 ± 10 48 ± 13 47 ± 8 4.9 0.8 J1603+110 363 ± 18 831 ± 39 626 ± 55 0.6 16.8 10.9 J1606+133 95 ± 7 161 ± 9 137 ± 13 0.0 2.4 5.5 J1608+104 1196 ± 56 1686 ± 79 1412 ± 1 2 5 0.1 17.4 5.1 J1609+284 31 ± 11 37 ± 12 27 ± 5 37 ± 1 0.3 0.5 3.8 J1612+204 36 ± 17 31 ± 9 46 ± 6 0.4 2.0 J1618+489 19 ± 12 44 ± 10 21 ± 4 66 ± 2 0.9 1.8 2.8 J1624+568 159 ± 7 213 ± 9 183 ± 16 2.0 0.1 4.8 J1631+108 126 ± 9 209 ± 11 145 ± 13 0.1 2.1 5.8 J1630+741 86 ± 5 139 ± 6 116 ± 10 300 ± 9 0.8 5.7 2.6 6.8 J1649+681 16 ± 4 50 ± 5 39 ± 5 3.1 1.4 5.3 J1656+533 105 ± 6 174 ± 8 145 ± 13 2.7 2.0 7.1 J1657+481 604 ± 24 847 ± 33 738 ± 65 1064 ± 35 0.3 0.3 2.8 6.0 J1702+079 254 ± 14 117 ± 9 172 ± 16 1.2 2.3 8.5 J1700+685 341 ± 11 435 ± 13 380 ± 34 351 ± 12 -0.1 4.7 1.5 5.6 J1711+541 203 ± 9 123 ± 6 172 ± 15 3.0 0.1 7.5 J1716+689 251 ± 8 314 ± 10 286 ± 25 2.6 2.1 4.9 J1716+686 732 ± 21 988 ± 28 838 ± 74 508 ± 17 -0.4 3.1 4.2 7.2 J1717+743 103 ± 5 139 ± 6 125 ± 11 432 ± 14 1.0 0.7 2.3 4.7 Appendix A. Short Term Variable Tables N A M E Fae Far F6 F20 a -logQse -logQsr Va J1722+610 151 ± 6 321 ± 11 245 ± 22 157 ± 5 -0.4 4.6 0.9 12.9 J1732+009 155 ± 11 78 + 9 98 ± 10 1.4 2.2 5.5 J1740+438 146 ± 8 234 ± 10 196 ± 17 2.0 0.0 6.8 J1740+521 2316 ± 85 1133 ± 42 1699 ± 1 5 1 4.0 1.2 12.4 J1745+670 248 ± 8 321 ± 10 288 ± 25 713 ± 23 0.8 2.0 0.7 5.5 J1756+453 88 ± 6 34 + 5 59 ± 6 2.1 1.8 7.1 J1759+287 72 + 6 169 ± 9 134 ± 12 2.7 0.6 8.9 J1803+431 19 ± 12 38 + 9 30 ± 4 0.1 2.7 J1808+451 20 ± 10 33 ± 15 24 ± 5 0.1 2.1 J1810+016 175 ± 11 84 + 9 118 ± 12 0.2 3.0 6.3 J1814+228 18 + 7 40 + 7 29 ± 5 7.0 6.0 J1849+670 608 ± 18 992 ± 29 845 ± 75 529 ± 17 -0.4 2.8 4.0 11.1 J1851+499 5 ± 5 97 + 6 53 ± 6 0.3 2.2 12.3 J1852+489 219 ± 10 351 ± 14 311 ± 28 3.6 4.9 7.7 J1856+061 267 ± 14 149 ± 10 193 ± 18 0.1 4.5 6.8 J1924+286 140 ± 8 47 + 5 92 ± 9 2.8 4.5 9.5 J1956+635 364 ± 12 143 ± 6 136 ± 12 22.2 1.8 16.1 J2053+530 170 ± 8 106 ± 6 139 ± 13 3.0 0.8 6.6 J2055+613 307 ± 11 414 ± 14 385 ± 34 3.7 4.3 5.9 J2102+470 229 ± 10 137 ± 7 170 ± 15 0.6 2.7 7.5 J2115+367 71 ± 6 136 ± 8 110 ± 10 1.6 13.4 6.8 J2140+107 32 + 6 92 + 8 57 + 7 2.6 0.3 6.1 J2145+187 45 + 6 88 + 7 71 + 7 79 ± 2 0.1 2.6 2.2 4.8 J2147+153 763 ± 36 1080 ± 50 927 ± 82 2.1 0.6 5.1 J2152+653 76 + 5 111 ± 6 92 ± 9 8.5 1.2 4.8 J2201+248 31 + 5 72 + 6 62 ± 7 2.1 0.4 5.0 J2201+508 649 ± 25 916 ± 35 820 ± 73 0.3 4.0 6.3 J2202+292 71 + 6 116 ± 7 97 ± 9 3.0 4.6 4.8 J2208+615 47 + 4 92 + 5 67 ± 7 3.5 5.7 6.4 J2240+515 141 ± 7 193 ± 9 169 ± 15 0.3 2.7 4.8 J2251+440 79 + 6 127 ± 7 104 ± 10 5.0 0.6 5.3 J2258+496 63 + 5 103 ± 6 87 ± 8 5.6 0.5 5.0 J2327+096 508 ± 25 738 ± 35 643 ± 57 4.8 0.8 5.4 J2350+111 291 ± 15 192 ± 11 247 ± 22 2.1 0.1 5.4 J0002+749 77 + 5 113 ± 6 96 ± 9 2.1 1.5 4.8 Appendix A. Short Term Variable Tables 99 A.3 Short Term Variable SIMBAD Matches N A M E Class Position (J2000) Distance J0019+734 Radio 0:19:45.70 +73:27:30.2 3.70 J0121+118 QSO 1:21:41.52 +11:49:50.6 14.90 J0202+397 Radio 2: 2: 1.63 +39:43:20.6 4.80 J0228+673 QSO 2:28:50.05 +67:21: 3.0 6.30 J0310+382 Radio 3:10:49.88 +38:14:53.9 4.60 J0326+287 R S C V n 3:26:35.09 +28:42:59.3 8.70 J0332+545 Pulsar 3:32:59.31 +54:34:44.0 0.50 J0431+206 RadioG 4:31: 3.69 +20:37:34.2 0.90 J0449+635' QSO 4:49:23.25 +63:32: 9.5 1.00 J0502+388 Radio 5: 2:32.45 +38:49:52.5 2.40 J0714+146 RadioG 7:14: 4.64 +14:36:22.6 1.90 J0738+177 BLLac 7:38: 7.39 +17:42:19.0 0.80 J0957+553 QSO 9:57:38.67 +55:22:58.9 4.80 J0958+655 BLLac 9:58:47.24 +65:33:54.8 0.70 J1031+746 Radio 10:31:22.16 +74:41:57.9 0.70 J1037+571 BLLac 10:37:44.50 +57:11:54.0 3.10 J1048+717 A G N 10:48:27.58 +71:43:35.6 0.50 J1112+350 Radio 11:12:33.25 +35: 3:38.6 1.30 J1127+568 QSO 11:27:40.16 +56:50:14.8 0.70 J1236+393 Radio 12:36:51.36 +39:20:28.1 2.20 J1243+732 Galaxy 12:43:11.16 +73:15:59.2 4.10 Appendix A. Short Term Variable Tables 100 N A M E Class Position (J2000) Distance J1256+350 Radio 12:56:11.19 +35: 2:17.6 1.40 J1355+304 QSO 13:55:40.81 +30:24: 8.6 4.20 J1419+383 Radio 14:19:46.47 +38:21:48.1 0.90 J1434+420 Radio 14:34: 5.70 +42: 3:16.0 0.90 J1437+381 Radio 14:37:33.36 +38: 7:44.8 0.10 J1520+745 Radio 15:20:42.85 +74:35:42.2 4.00 J1549+214 RadioG 15:49:48.94 +21:25:38.8 11.40 J1608+104 QSO 16: 8:46.20 +10:29: 7.8 3.70 J1630+741 Radio 16:30:25.83 +74: 9:33.5 2.80 J1657+481 Galaxy 16:57:46.81 +48: 8:33.1 1.10 J1700+685 Radio 17: 0: 9.02 +68:30: 5.7 1.40 J1716+689 Radio 17:16: 9.14 +68:56:14.1 6.30 J1716+686 QSO 17:16:13.81 +68:36:38.3 0.60 J1717+743 Radio 17:17:38.37 +74:18:41.7 2.80 J1740+521 QSO 17:40:36.98 +52:11:43.4 5.70 J1849+670 QSO 18:49:15.94 +67: 5:42.8 2.00 J1852+489 QSO 18:52:28.39 +48:55:47.5 9.80 J2102+470 Radio 21: 2:17.01 +47: 2:16.4 12.40 J2147+153 RadioG 21:47:25.07 +15:20:32.1 20.30 J2201+508 Radio 22: 1:42.62 +50:49: 1.4 12.80 J2240+515 Star 22:40:17.65 +51:32:51.2 21.50 Appendix A. Short Term Variable Tables AA Short T e r m Variable NED Matches N A M E Radio X-ray QSO Galaxy Other J0005+544 • J0019+734 2 • J0042+544 • J0047+569 J0049+343 • J0120+265 J0121+118 • J0128+490 • J0202+397 VisS J0228+673 Blue J0249+221 J0258+056 • J0302+535 • J0304+683 J0310+391 J0310+382 • J0323+462 J0325+224 J0332+545 J0340+540 2 J0357+418 3 J0411+087 2 J0424+006 4 • • J0431+206 5 • J0440+146 • J0445+072 2 J0449+635 2 • J0502+388 • Appendix A. Short Term Variable Tables N A M E Radio X-ray QSO Galaxy Other J0502+346 • J0518+331 • J0530+550 • J0607+712 2 J0606+146 2 J0714+146 4 • J0716+367 2 J0737+645 • J0738+177 8 2 • AbLS GammaS IrS J0751+272 2 J0839+033 3 • J0849+098 6 J0856+717 • J0903+636 • J0939+421 • J0943+435 • J0944+520 2 • J0957+553 7 • • J0958+655 3 • • GammaS J1015+558 • J1016+052 4 VisS(2) J1031+746 2 • J1030+515 • J1048+717 2 • J1106+282 • J1106+172 • J1112+350 • J1120+126 • J1125+399 2 Appendix A. Short Term Variable Tables 103 N A M E Radio X-ray QSO Galaxy Other J1127+568 3 • J1205+008 3 J1206+527 • • SN IrS J1221+083 • J1222+042 6 2 • J1236+393 3 J1243+398 • J1243+732 2 • J1256+350 2 J1300+234 3 J1303+513 • • J1307+064 • J1318+044 2 J1355+304 • • J1356+405 2 J1403+637 3 J1419+383 2 • J1434+420 2 • J1437+381 2 • EmLS J1508+414 2 J1520+745 2 J1549+214 • GLens J1603+110 • J1608+104 7 • • J1618+489 • J1624+568 2 J1630+741 3 J1656+533 • J1657+481 3 Appendix A. Short Term Variable Tables NAME Radio X-ray QSO Galaxy Other J1702+079 • J1700+685 3 J1711+541 • J1716+689 5 J1716+686 4 • • J1717+743 4 J1722+610 • J1732+009 5 J1740+521 5 • • GammaS J1745+670 3 J1803+431 • J1810+016 • .J1849+670 AbLS J1852+489 2 • J1924+286 J1956+635 J2055+613 J2102+470 VisS J2115+367 J2145+187 . J2147+153 7 • J2152+653 2 J2201+248 • J2201+508 • J2202+292 • J2240+515 • J2251+440 3 J2327+096 5 • • J2350+111 • Appendix A. Short Term Variable Tables 1 0 5 A . 5 Short Term Variable APS Counterparts N A M E Class Position (J2000) Distance Magnitude Colour J0258+056 Star 2:58:50.54 + 5:41:08.12 0.92 20.26 -0.38 J0430+169 Star 4:30:22.28 +16:55:04.30 1.08 20.62 2.48 J0445+072 Galaxy 4:45:01.45 + 7:15:53.64 0.74 20.84 0.94 J0449+635 Star 4:49:23.16 +63:32:10.28 1.93 20.36 1.42 J0716+367 Galaxy 7:16:37.10 +36:42:19.22 1.25 16.53 1.94 J0737+645 Star 7:37:58.96 +64:30:43.16 0.18 20.84 4.32 J0856+717 Star 8:56:54.83 +71:46:23.52 1.77 19.65 0.52 J0958+655 Star 9:58:47.27 +65:33:54.43 0.58 16.82 0.78 J1031+746 Galaxy 10:31:22.78 +74:41:56.26 2.76 17.53 1.50 J1048+717 Star 10:48:27.58 +71:43:35.40 0.31 19.08 0.66 J1106+282 Star 11:06:07.26 +28:12:46.33 1.09 19.42 0.36 J1153+251 Galaxy 11:53:18.12 +25:09:04.39 0.53 22.41 1.86 J1309+524 Star 13.09:07.98 +52:24:37.30 1.11 18.38 0.52 J1355+304 Star 13:55:41.11 +30:24:11.23 0.82 18.73 0.50 J1609+284 Star 16:09:40.27 +28:28:47.24 2.12 19.77 0.12 J1722+610 Star 17:22:40.01 +61:05:59.24 0.69 19.41 0.02 

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