GRB 210121A: A Typical Fireball Burst Detected by Two Small Missions

Abstract

The Chinese CubeSat Mission, Gamma Ray Integrated Detectors (GRID), recently detected its first gamma-ray burst, GRB 210121A, which was jointly observed by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM). This burst is confirmed by several other missions, including Fermi and Insight-HXMT. We combined multi-mission observational data and performed a comprehensive analysis of the burst's temporal and spectral properties. Our results show that the burst is special in its high peak energy, thermal-like low energy indices, and large fluence. By putting it to the E p -E γ,iso relation diagram with assumed distance, we found this burst can be constrained at the redshift range of [0.3,3.0]. The thermal spectral component is also confirmed by the direct fit of the physical models to the observed spectra. Interestingly, the physical photosphere model also constrained a redshift of z ∼ 0.3 for this burst, which help us to identify a host galaxy candidate at such a distance within the location error box. Assuming the host galaxy is real, we found the burst can be best explained by the photosphere emission of a typical fireball with an initial radius of r 0 ∼ 6.7 × 10 7 cm.

Kilonova and Optical Afterglow from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational-wave Triggers

“…Among these potential associated EM signals of BNS GW events, kilonovae are the most expected EM sources for astronomers to search after GW triggers. The observations of sGRBs would achieve all-sky coverage by the Gamma Ray Integrated Detectors (GRID Wen et al 2019;Wang et al 2021) and the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM; Zhang et al 2018b;Wang et al 2021), which can cooperate on the constraint of the sky location for BNS GW alerts. However, for onaxis or near-on-axis observers, the presence of bright jet afterglows may affect the observations of kilonovae.…”