GRB 160821B late afterglow rebrightening: A new candidate for magnetar-powered Merger-novae

Abstract

For the first time on August 17, 2017, the LIGO-Virgo scientific collaboration detected a gravitational wave (GW) signal from a binary neutron star (BNS) merger event (i.e., GW170817), along with its multiwavelength electromagnetic counterparts. The detection of GW170817 confirmed that the BNS merger can produce both Gamma-ray Bursts (GRBs) and Merger-novae. Therefore, searching for the Merger-novae signature could help to justify whether those short GRBs without the detected GW parts are indeed resulting from the merger process of double compact stars. In this study, we thoroughly investigate the special characteristics of GRB 160821B's afterglow (including its internal X-ray plateau, late optical, and simultaneous X-ray rebrightening). We found that its multiband afterglow data could be well-interpreted by invoking magnetar dipole radiation, external shock afterglow emission and magnetar-powered Merger-novae radiation, inferring that the rebrightening signature of GRB 160821B is a novel candidate for magnetar-powered Merger-novae. The discovery of Merger-novae candidates, or GRBs, is important as they can provide an important basis for studying the merger rate of compact binary stars at high redshift, which is essential for studying the origin of heavy elements in the universe.