Dr Kaustubh Rajwade

Abstract:

Most population studies of pulsars have hitherto focused on the disc of the Galaxy, the Galactic centre, globular clusters, and nearby galaxies. It is expected that pulsars, by virtue of their natal kicks, are also to be found in the Galactic halo. We investigate the possible population of canonical (i.e. non-recycled) radio pulsars in the halo, estimating the number of such pulsars, and the fraction that is detectable via single pulse and periodicity searches. Additionally, we explore the distributions of flux densities and dispersion measures (DMs) of this population. We also consider the effects of different velocity models and the evolution of inclination angle and magnetic field on our results. We show that ∼33  % of all pulsars beaming towards the Earth are in the halo but the fraction reduces to ∼1.5  % if we let the inclination angle and the magnetic field evolve as a falling exponential. Moreover, the fraction that is detectable is significantly limited by the sensitivity of surveys. This population would be most effectively probed by surveys using time-domain periodicity search algorithms. The current non-detections of pulsars in the halo can be explained if we assume that the inclination angle and magnetic field of pulsars evolve with time. We also highlight a possible confusion between bright pulses from halo pulsars and fast radio bursts with low DMs where further follow-up is warranted.

Abstract:

ALFABURST has been searching for fast radio bursts (FRBs) commensally with other projects using the Arecibo L-band Feed Array receiver at the Arecibo Observatory since 2015 July. We describe the observing system and report on the non-detection of any FRBs from that time until 2017 August for a total observing time of 518 h. With current FRB rate models, along with measurements of telescope sensitivity and beam size, we estimate that this survey probed redshifts out to about 3.4 with an effective survey volume of around 600 000 Mpc 3 . Based on this, we would expect, at the 99 per cent confidence level, to see at most two FRBs. We discuss the implications of this non-detection in the context of results from other telescopes and the limitation of our search pipeline. During the survey, single pulses from 17 known pulsars were detected. We also report the discovery of a Galactic radio transient with a pulse width of 3 ms and dispersion measure of 281 pc cm -3 , which was detected while the telescope was slewing between fields.