http://arxiv.org/abs/2111.03686
Multi-messenger probes of BHNS and NSNS mergers are important for our understanding of the properties of these compact objects and the extreme physical domain they inhabit. While SGRBs and kilonovae are the most considered counterpart to these mergers, both require disruption of the NS, which may not occur in BHNS systems. We investigate the properties of an EM counterpart that does not require tidal disruption: resonant shattering flares (RSFs).
We find that RSFs are short (duration $\sim 0.1 \text{ s}$) non-thermal flares with luminosities up to a few $\times10^{48}\text{ erg/s}$ that are strongly dependent on the magnetic field strength at the surface of the NS. These flares are a result of multiple colliding relativistic shells launched during the resonance window, leading to a prompt non-thermal gamma-ray emission, as well as broad-band afterglow emission.
We compute the expected rates of detectable RSFs using the BPASS population synthesis code, with different assumptions about the evolution of surface magnetic field strengths before merger. We find the rate of detectable RSFs to be $\sim 0.0001-5$ per year for BHNS mergers and $\sim 0.0005-25$ per year for NSNS mergers, with the lower bound corresponding to surface field decay consistent with magneto-thermal evolution in purely crustal fields, while the upper bounds are for systems which have longer-lived surface magnetic fields supported by flux frozen into the core. If some of the observed SGRB precursor flares are indeed RSFs, this suggests the presence of a longer-lived surface field for some fraction of the neutron star population, and that we should expect RSFs to be the most common detectable EM counterpart to GW detections of BHNS mergers. The non-detection of a RSF prior to GRB170817A provides an upper bound for the magnetic fields for the progenitor NSs of $B_{\rm surf}~\sim 10^{13} {\rm G}$.
D. Neill, D. Tsang, H. Eerten, et. al.
Tue, 9 Nov 21
59/102
Comments: 16 pages, 12 figures, submitted to MNRAS
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