Magnetar Central Engine and Possible Gravitational Wave Emission of Nearby Short GRB 160821B

GRB 160821B is a short gamma-ray burst (SGRB) at redshift z = 0.16, with a duration less than 1 s and without any "extended emission" detected up to more than 100 s in both Swift/BAT and Fermi/GBM bands. An X-ray plateau with a sharp drop 180 s after the BAT trigger was observed with 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 to B-p < 3.12 x 10(16) G and initial spin period to P-0 < 8.5 x 10(-3) s. Its equation of state is consistent with the GM1 model with M-TOV similar to 2.37 circle dot Me and ellipticity is an element of< 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).National Basic Research Program (973 Programme) of China [2014CB845800]; National Natural Science Foundation of China [11603006, 11533003, 11503011]; One-Hundred-Talents Program of Guangxi colleges, Guangxi Science Foundation [2016GXNSFCB380005, 2013GXNSFFA019001]; High level innovation team and outstanding scholar program in Guangxi colleges; Scientific Research Foundation of GuangXi University [XGZ150299]SCI(E)ARTICLE283