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Radio observations of two binary pulsars Kasian, Laura Elizabeth

Abstract

The study of pulsars in binary systems produces a wide variety of scientific results, including unique tests of general relativity and constraints on the equation of state of matter at extremely high densities. Through pulsar timing (which utilizes the fact that pulsars are precise clocks), it is possible to precisely measure the orbital parameters and masses of some binary pulsars, which can place constraints on their mass transfer histories. We present timing results for two binary pulsars. The intermediate-mass binary pulsar (IMBP) PSR J0621+1002 is a mildly recycled pulsar in an 8.3-day orbit around a massive white dwarf (WD) companion. It is one of only two known IMBPs with a precise mass measurement. We collected 9 days' worth of data using the 305-metre Arecibo telescope (allowing for full orbital coverage), which we used to improve constraints on the advance of periastron, and in turn, the pulsar and companion masses (to 1.53^{+0.10}_{-0.20}M☉ and 0.76^{+0.28}_{-0.07} solar masses, respectively) and inclination angle of the system. These results, combined with the relatively long orbital period, suggest a disk accretion evolutionary scenario involving short-lived periods of hyper-accretion, in which a moderate amount of mass has been transferred to the neutron star (NS). PSR J1906+0746 is a young pulsar in a compact ~4-hour orbit around a companion that was discovered in the early stages of the PALFA survey using the 305-metre Arecibo telescope. We present the timing results using data collected between 2005 to 2009 using the Green Bank, Arecibo, and Nançay telescopes. We have measured the advance of periastron, the time dilation and gravitational redshift parameter, and the orbital decay, and we find the pulsar and companion masses to be 1.323^{+0.011}_{-0.011}M☉ and 1.290^{+0.011}_{-0.011} solar masses, respectively. Although the companion may be a second NS, it is more likely to be a massive WD. The system's evolution probably involved a substantial transfer of mass from the WD progenitor onto the NS progenitor through Roche-lobe overflow accretion, followed by the formation of the WD, and a short common envelope phase, and finally the ejection of the envelope and the pulsar-forming supernova.

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