Coherent radio precursors to neutron star mergers

The Department of Physics is pleased to welcome Navin Sridhar for a presentation as part of the Gravitational Wave Seminar Series. Navin comes to us from Columbia University. His research interests are in understanding the physics of particle energization in astrophysical plasmas, accretion around compact objects, emission mechanisms of high energy non-thermal X-rays from black hole coronae and the origin of coherent radio emission from sources like Pulsars and Fast Radio Bursts.

Abstract:

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 emission of ms-second duration prior to binary NS merger. We calculate the light curves and spectra of such a precursor using results from our hydro and particle-in-cell simulations. 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. This can serve as a potential EM counterpart to LIGO events of BNS or BHNS mergers with no associated GRB.