Magnetar central engine and possible gravitational wave emission of nearby short GRB 160821B

TL;DR

This paper models the central engine of short GRB 160821B as a newly formed magnetar, constraining its properties, and discusses the potential detectability of its gravitational wave emission with future detectors.

Contribution

It proposes a magnetar central engine model for the short GRB and estimates its magnetic field, spin period, and gravitational wave emission prospects.

Findings

Magnetar surface magnetic field constrained to <3.12×10^16 G

Initial spin period constrained to <8.5×10^-3 seconds

Gravitational waves may be detectable by Einstein Telescope at 100 Mpc

Abstract

GRB 160821B is a short gamma-ray burst (GRB) at redshift $z=0.16$, with a duration less than 1 second and without detection of any "extended emission" up to more than 100 seconds in both {\em Swift}/BAT and {\em Fermi}/GBM bands. An X-ray plateau with a sharp drop 180 seconds after the BAT trigger was observed with {\em Swift}/XRT. No supernova or kilo-nova signature was detected. Assuming the central engine of this SGRB is a recently born supra-massive magnetar, we can explain the SGRB as jet radiation and its X-ray plateau as the internal energy dissipation of the pulsar wind as it spins down. We constrain its surface magnetic field as $B_{\rm p}<3.12\times 10^{16}$ G and initial spin period as $P_0< 8.5\times 10^{-3}$ seconds. Its equation of state is consistent with the GM1 model with $M_{\rm TOV} \sim 2.37 M_\odot$ and ellipticity $\epsilon<0.07$. Its gravitational wave (GW) radiation may be detectable with the future Einstein Telescope, but is much weaker than the current detectability limit of advanced-LIGO. The GW radiation of such an event would be detectable by advanced-LIGO if it occurred at a distance of 100 Mpc ($z=0.023$).