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 .