GRB 230204B: GIT discovery of a fast fading afterglow associated with an energetic gamma-ray burst from a massive star progenitor

Abstract

We present a comprehensive multiwavelength study of a bright gamma-ray burst GRB 230204B, analyzing both prompt and afterglow emissions. This GRB is highly energetic, with an isotropic equivalent energy emission of Eiso ∼ 2.2 × 1054 erg released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow (mr = 15.55) that fades rapidly (∝t−1.82). The prompt emission shows a strong thermal photospheric emission along with a nonthermal high-energy component. We explore the evolution of these components and find them to be consistent with the theoretical expectations of the fireball model. Afterglow modeling reveals an energetic jet (Eγ ≳ 1052 erg) expanding into a wind-type medium viewed nearly on-axis, suggesting a massive star progenitor with strong winds. We also explore correlations between the prompt emission and afterglow that may help to place GRB 230204B within the broader context of the long GRB population.