Ground-Based Wide Angle Camera Array Detects Immediate Optical Emission of Gamma-Ray Burst

A team of researchers led by Dr. XIN Liping from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has detected the prompt optical emission and its transition to the early afterglow of a gamma-ray burst (GRB 201223A) using the Ground Wide Angle Camera Array (GWAC) located at Xinglong Observatory of NAOC. Gamma-ray bursts are produced by the collapse of massive stars or the merger of binary neutron stars. They are accompanied by extreme relativistic jets emitting enormous amounts of energy within a few seconds of the bursts. The phenomenon includes the prompt emission caused by the shock in the jet and the afterglow produced by interaction between the jet and external medium. GWAC, proposed and led by Prof. WEI Jianyan, principal investigator of the Space-based Multi-band Astronomical Variable Objects Monitor (SVOM) mission, is one of the key ground-based telescopes for the SVOM project. It can cover an ultra-large sky area with a temporal resolution of 15 seconds and a detection capability of magnitude 16. Its scientific purpose is to conduct systematic research on the prompt optical emission of GRBs discovered by the SVOM mission. The extremely early unique data provided by GWAC place a fine constraint on the characteristics of the progenitor. Scientists expect strong stellar winds around a massive star, which is thought to be the ideal progenitor of a gamma-ray burst. However, the stellar wind is quite small for this event, even at a very close distance from the burst, thus suggesting the progenitor has a small stellar mass.