Gravitational wave signal of the short rise fling of galactic runaway pulsars

Abstract

Determination of pulsar parallaxes and proper motions addresses fundamentalastrophysical open issues. Here, after scrutinizing the ATNF Catalog searching for pulsardistances and proper motions, we verify that for an ATNF sample of 212 galactic runawaypulsars (RAPs), which currently run across the Galaxy at very high speed and undergolarge displacements, some gravitational wave (GW) signals produced by such presentaccelerations appear to be detectable after calibration against the Advanced LIGO (LIGOII). Motivated by this insight, we address the issue of the pulsar kick at birth,or the short rise fling from a supernova explosion, by adapting the theory foremission of GW by ultrarelativistic sources in this case in which the Lorentz factor isγ∼1. We show that during the short rise fling each runaway pulsar (RAP) generates a GWsignal with characteristic amplitude and frequency that makes it detectable by current GWinterferometers. For a realistic analysis, an efficiency parameter is introduced to quantifythe expenditure of the rise fling kinetic energy, which is estimated from the linearmomentum conservation law applied to the supernova explosion that kicks outthe pulsar. The remaining energy is supposed to be used to make the star spin.Thus, a comparison with the spin of ATNF pulsars having velocities in the range400–500 km s−1 is performed. The resulting difference suggests that other mechanisms (like differentialrotation, magnetic breaking or magneto-rotational instability) should dissipate part of thatenergy to produce the observed pulsar spin periods. Meanwhile, the kick phenomenon mayalso occur in globular and open star clusters at the formation or disruption of very shortperiod compact binary systems wherein abrupt velocity and acceleration similar to thosegiven to RAPs during the short rise fling can be imparted to each orbital partner. To betteranalyze these cases, pulsar astrometry from micro-to nano-arcsec scales might be of greathelp. In the case of a supernova, the RAP GW signal could be a benchmark for the GWsignal from the core collapse.