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UBC Theses and Dissertations

A survey of the galactic plane for variable radio emission Taylor, A. R.


Observations have been carried out to survey the northern galactic plane for sources of highly variable radio emission at 5 GHz. To over—come the biases of previous searches for variability, the survey is conducted by making repeated and systematic observations of the survey region, consisting of the area within about ±2° of the galactic plane in the longitude interval of 40° to 220°. This thesis presents the analysis and results of the first three years of observations, comprising 40% of the total survey. The observations were carried out for a total of 3 months, in August of 1977, 1978 and 1979, and cover an area of over 200 square degrees, with a resolution of 3'. Within this area, a total of 806 compact radio sources have been detected. The catalogue includes sources with flux density as low as 15 mJy, and is complete down to 70 mJy. Of these sources, 758 have been examined for variation on a time scale of a few days (short—term), and 434 for variations on time scales of one or two years (long—term). Twenty—three new variable radio sources have been discovered; 12 short—term and 11 long—term. An additional 18 sources are possibly variable. The amplitudes of the long—term variations are similar to those of known extragalactic variables. A number of short—term variables exhibit much larger variations. The longitude distribution suggest that the majority of short—term variables are galactic, with luminosities in the range 10³⁰—10³⁵ ergs—s⁻¹. This luminosity range is similar to that of the strong X—ray binaries sources, such as Cyg X-3, SS 433 and Sco X-1. To date, extensive follow—up observations have been carried out for only one of the variable sources discovered. This source (GT0236+610) is periodic, undergoing a radio outburst every 26.52 days. The source is positionally co-incident with the BO star LS 1+61°303 and this identification has been confirmed by Gregory et al. (1979). GT0236+610 is an X-ray source (Share et al. 1978, Bignami et al. 1980) and, in addition, is the most probable counterpart of the COS B ƴ-ray source CG135+01 (Gregory and Taylor 1978, Pollock et al. 1981 ). Another highly variable source (GT2116+493) is also found to be co—incident with a stellar object. This source is probably an RS CVn type binary at a distance of about 300 pc. Comparison of source counts from the catalogue of compact sources, to extragalactic results, show that >200 of the compact sources, with flux density less than 60 mJy, are galactic. The non—variable galactic sources are likely to be small HII regions within 6 kpc of the sun.

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