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arXiv · 2512.03136

GRB 230204B: GIT Discovery of a Fast Fading Afterglow Associated with an Energetic GRB from a Massive-Star Progenitor

Vishwajeet Swain·Varun Bhalerao·Harsh Kumar·Mehul Goyal·Ankur Ghosh·Utkarsh Pathak·Poonam Chandra·Tomas Ahumada·G. C. Anupama·Suman Bala·Sudhanshu Barway·Joshua S. Bloom·Dimple Dimple·Viraj R. Karambelkar·Mansi M. Kasliwal·Kuntal Misra·Josiah Purdum·Divita Saraogi·Jesper Sollerman·Aswin Suresh·Stefan J. van der Walt·Gaurav Waratkar
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Abstract

We present a comprehensive multi-wavelength 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 $E_{\mathrm{iso}} \sim 2.2 \times 10^{54}\ \mathrm{erg}$, released during the prompt emission. The GROWTH-India Telescope discovered a bright afterglow ($m_r = 15.55$) that faded rapidly ($\propto t^{-1.82}$). The prompt emission shows strong thermal photospheric emission, along with a non-thermal high-energy component. We explore the evolution of these components and find them to be consistent with theoretical expectations. Afterglow modeling reveals an energetic jet $E_{tot} \gtrsim 10^{52}\ \mathrm{erg}$ 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 understand the complete picture of GRB progenitors.

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Vishwajeet Swain, Varun Bhalerao, Harsh Kumar, Mehul Goyal, Ankur Ghosh, Utkarsh Pathak, Poonam Chandra, Tomas Ahumada, G. C. Anupama, Suman Bala, Sudhanshu Barway, Joshua S. Bloom, Dimple Dimple, Viraj R. Karambelkar, Mansi M. Kasliwal, Kuntal Misra, Josiah Purdum, Divita Saraogi, Jesper Sollerman, Aswin Suresh, Stefan J. van der Walt, Gaurav Waratkar. 2025-12-02. GRB 230204B: GIT Discovery of a Fast Fading Afterglow Associated with an Energetic GRB from a Massive-Star Progenitor. https://doi.org/10.3847/1538-4357/ae459f

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