A search for radio pulsars and fast transients in M31 using the Westerbork Synthesis Radio Telescope

Abstract

We present the results of the most sensitive and comprehensive survey yet undertaken for radio pulsars and fast transients in the Andromeda galaxy (M31) and its satellites, using the Westerbork Synthesis Radio Telescope (WSRT) at a central frequency of 328 MHz. We used the WSRT in a special configuration called 8gr8 (eight-grate) mode, which provides a large instantaneous field-of-view, about 5 square degrees per pointing, with good sensitivity, long dwell times (up to 8 hours per pointing), and good spatial resolution (a few arc minutes) for locating sources. We have searched for both periodicities and single pulses in our data, aiming to detect bright, persistent radio pulsars and rotating radio transients (RRATs) of either Galactic or extragalactic origin. Our searches did not reveal any confirmed periodic signals or bright single bursts from (potentially) cosmological distances. However, we do report the detection of several single pulse events, some repeating at the same dispersion measure, which could potentially originate from neutron stars in M31. One in particular was seen multiple times, including a burst of six pulses in 2000 seconds, at a dispersion measure of 54.7 pc cm −3 , which potentially places the origin of this source outside of our Galaxy. Our results are compared to a range of hypothetical populations of pulsars and RRATs in M31 and allow us to constrain the luminosity function of pulsars in M31. They also show that, unless the pulsar population in M31 is much dimmer than in our Galaxy, there is no need to invoke any violation of the inverse square law of the distance for pulsar fluxes.

LOFAR radio search for single and periodic pulses from M 31

“…A similar blind search through the 2014 data found no convincing pulsar signals from M31, M32 or M110. A close inspection of even low-significance single-pulse detections around DM=54.7 pc cm −3 could not confirm the Rubio-Herrera et al (2013) candidate.…”

“…The DM = 54.7 pc cm −3 bursts identified in Rubio-Herrera et al (2013) were recorded in a wide-field WSRT mode called 8gr8 (Janssen et al, 2009). This created 8 tied-array beams, each offset within the grating response of the linear WSRT array.…”

Search for transient gravitational waves in coincidence with short-duration radio transients during 2007–2013

“…In some cases this was because they occurred during times before sensitive GW data were available [33,56]. This includes the original Lorimer burst [39].…”

Do pulsar radio fluxes violate the inverse-square law?

“…However, the result of S09 has been disputed by the pulsar community (Lorimer 2011). If the pulsar flux varied more slowly than an inverse-square law, one would have discovered a large number of pulsars in M31 or M33, whereas no confirmed detections have been made (McLaughlin & Cordes 2003;Bhat et al 2011;Rubio-Herrera et al 2013). Nevertheless, it is possible that the non-detection of pulsars from these nearby galaxies could be due to other reasons such as: large pulse smearing or interstellar scattering along the line of sight; or the IMF and star formation rate in M31/M33 could be different from that in our galaxy; or accretion from dark matter could destroy the neutron star population (Bramante & Linden 2014), etc.…”