Double Neutron Star Merger In The Off-axis Observation Effect Of Optics And Near-infrared

Gamma-ray bursts(GRBs)are extremely energetic explosions that occur in the universe.According to the duration,we divided them into long gamma-ray bursts and short gamma-ray bursts.It is generally agreed that the progenitors of long GRBs are high-mass star collapse.The most popular model for SGRBs is the coalescence of binary neutron stars(BNSs),which is also expected to be the promising sources producing strong gravitational wave emission.GW170817 is the first direct detection of the gravitational-wave radiation with electromagnetic signal GRB 170817A,which marks the start of multi-messenger astronomy.In this paper,we introduce the background of GRBs,and during the merger of BNSs,different components such as relativistic jet and shock-breakout ejecta,cocoon,tidal ejecta,viscous-and neutrino-winds interacting with surrounding interstellar medium will produce luminous optical/near-infrared(NIR)emission.We have numerically estimated these expected optical/NIR transients viewing at different angles.The predicted brightness depends strongly on the viewing angles,the circumburst medium density,the kinetic energy as well as the velocity of the outflow.At the distance of DL=200 Mpc,the optical emission from the ultra-relativistic jet is the strongest at all densities viewing on-axis and off-axis with small observed angles.The orphan emission is dominated by the mildly relativistic shock-breakout ejecta at larger viewing angle.We also compare the kilonova emission with that of jet,shock-breakout ejecta and cocoon in NIR band.The on-and off-axis optical emission can be detectable with the ongoing and planned wide-field telescopes,ASAS-SN,iPTF,Pan-STARRS and LSST.GRB 170817A is the first SGRB signal from the double neutron star merger with direct detection of the gravitational-wave radiation and kilonova emission(AT 2017gfo).We show that strengthening the potential“connection”between GRB 170817A and GRB 130603B,and the extremely dim emission but long-lasting afterglow emission of GRB 170817A may suggest a low density of its circumburst medium.We then discuss whether GRB 070923,GRB 080121,GRB 090417A,GRB 111005A,and GRB 170817A form a new group of very nearby underluminous GRBs originated from neutron star mergers and compare the kilonova.They are strongly suggests that the kilonova from neutron star mergers are significantly diverse.