Shock-powered radio precursors of neutron star mergers from accelerating relativistic binary winds

During the final stages of a compact object merger, if at least one of the binary components is a magnetized neutron star (NS), then its orbital motion substantially expands the NS's open magnetic flux - and hence increases its wind luminosity - relative to that of an isolated pulsar. As the binary orbit shrinks due to gravitational radiation, the power and speed of this binary-induced inspiral wind may (depending on pair loading) secularly increase, leading to self-interaction and internal shocks in the outflow beyond the binary orbit. The magnetized forward shock can generate coherent radio emission via the synchrotron maser process, resulting in an observable radio precursor to binary NS merger. We perform 1D relativistic hydrodynamical simulations of shock interaction in the accelerating binary NS wind, assuming that the inspiral wind efficiently converts its Poynting flux into bulk kinetic energy prior to the shock radius. This is combined with the shock maser spectrum from particle-in-cell simulations, to generate synthetic radio light curves. The precursor burst with a fluence of similar to 1 Jy.ms at similar to GHz frequencies lasts similar to 1-500 ms following the merger for a source at similar to 3 Gpc (B-d/10(12) G)(8/9), where B-d is the dipole field strength of the more strongly magnetized star. Given an outflow geometry concentrated along the binary equatorial plane, the signal may be preferentially observable for high-inclination systems, that is, those least likely to produce a detectable gamma-ray burst.

Automated summary

Research shows that during the final stages of a compact object merger, if one of the binary components is a magnetized neutron star, it can lead to the shrinking of the binary orbit, increasing wind luminosity, and potentially producing a radio precursor. The precursor burst lasts for a short duration and its intensity depends on the source distance and magnetic field strength.