Electromagnetic Counterparts Of Gravitational Waves From Compact Binary Mergers

The hallmark event of gravitational wave GW170817 and its electromagnetic(EM)counterparts short gamma-ray burst SGRB 170817 A and kilonova AT 2017 gfo confirmed an association of gravitational waves(GWs),short gamma-ray bursts(SGRBs),and kilonove from binary neutron star mergers.Another hallmark event of fast radio burst FRB 200428 in association with a hard X-ray burst from Galactic magnetar SGR 1935+2154 established magnetar as a source that can produce fast radio bursts(FRBs).These events motivates people to seek out an association of GWs,SGRBs,and FRBs,since they are all likely related to magnetars theoretically and observationally.So I here treat FRBs as one type of EM counterpart of GWs from compact binary mergers.EM counterparts in a nutshell are outlined in Chapter I.In the following,I will briefly introduce our works and results relevant to EM counterparts roughly tracing the order of premerger-merger-postmerger of compact binary mergers.In Chapter II,for the first time,we find out a large sample—18 SGRBs with precursor from 660 SGRBs observed by Fermi and Swift satellites and carry out a comprehensive statistical analysis on their temporal and spectral features.Then we obtain some interesting statistical results and constrain the origins of precursors and study their probes for the progenitor properties of SGRBs by using these results.In Chapter III,we investigate EM emissions post a plunging spinning massive black hole(BH)–a strongly magnetized neutron star(NS)under the Wald charge scenario and find three possible mechanisms that could produce EM counterparts in a time interval of the BH's discharge post a BH–NS merger-induced GW event:(1)magnetic reconnection leading to a bright EM signal;(2)magnetic shock producing a bright radio emission like an FRB;or(3)the Blandford-Znajek mechanism giving rise to a luminous high-energy(X/?-ray)burst.In Chapter IV,we study whether magnetars could also be produced from neutron star–white dwarf(NSWD)mergers and apply to FRBs.By a preliminary calculation,we find that NSWD mergers with unstable mass transfer could result in the NS remnant acquiring an ultra-strong magnetic field via the dynamo mechanism due to differential rotation or envelope convection or possibly via the magnetic flux conservation of fossil field.If NSWD mergers can indeed create magnetars,then such channel could produce at least a subset of FRB 180924-like and FRB 180916.J0158+65-like FRBs.In Chapter V,under the assumption that SGR 1935+2154 and supernova remnant SNR G57.2+0.8 are physically related,by using the dispersion measure(DM)of FRB 200428 contributed by the foreground medium of our Galaxy and its local environments and combining other observations,we obtain that the distance of SGR1935+2154 turns out to be 9.0 ± 2.5 kpc.This is important to figure out the energy and luminosity of FRB 200428 and its associated X-ray burst so as to understand the physical mechanisms of FRBs.Finally,all works mentioned above are summarized,and some open questions and prospects are discussed in Chapter VI.