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arXiv · 2205.07790

Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM

M. D. Caballero-García·Rahul Gupta·S. B. Pandey·S. R. Oates·M. Marisaldi·A. Ramsli·Y. -D. Hu·A. J. Castro-Tirado·R. Sánchez-Ramírez·P. H. Connell·F. Christiansen·A. Kumar Ror·A. Aryan·J. -M. Bai·M. A. Castro-Tirado·Y. -F. Fan·E. Fernández-García·A. Kumar·A. Lindanger·A. Mezentsev·J. Navarro-González·T. Neubert·N. Østgaard·I. Pérez-García·V. Reglero·D. Sarria·T. R. Sun·D. -R. Xiong·J. Yang·Y. -H. Yang·B. -B. Zhang
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Abstract

We report on detailed multi-wavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor (ASIM) installed on the International Space Station (ISS) and the Gamma-ray Burst Monitor (GBM) on-board the Fermi mission. Our main goal is to understand the radiation mechanisms and jet composition of GRB 210619B. With a measured redshift of $z$ = 1.937, we find that GRB 210619B falls within the 10 most luminous bursts observed by Fermi so far. The energy-resolved prompt emission light curve of GRB 210619B exhibits an extremely bright hard emission pulse followed by softer/longer emission pulses. The low-energy photon indices ($\alpha_{\rm pt}$) values obtained using the time-resolved spectral analysis of the burst suggest a transition between the thermal (during harder pulse) to non-thermal (during softer pulse) outflow. We examine the correlation between spectral parameters and find that both peak energy and $\alpha_{\rm pt}$ exhibit the flux tracking pattern. The late time broadband photometric dataset can be explained within the framework of the external forward shock model with $\nu_m$ $< \nu_c$ $< \nu_{x}$ (where $\nu_m$, $\nu_c$, and $\nu_{x}$ are the synchrotron peak, cooling-break, and X-ray frequencies, respectively) spectral regime supporting a rarely observed hard electron energy index ($p<$ 2). We find moderate values of host extinction of E(B-V) = 0.14 $\pm$ 0.01 mag for the Small Magellanic Cloud (SMC) extinction law. In addition, we also report late-time optical observations with the 10.4 m GTC placing deep upper limits for the host galaxy ($z$=1.937), favouring a faint, dwarf host for the burst.

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M. D. Caballero-García, Rahul Gupta, S. B. Pandey, S. R. Oates, M. Marisaldi, A. Ramsli, Y. -D. Hu, A. J. Castro-Tirado, R. Sánchez-Ramírez, P. H. Connell, F. Christiansen, A. Kumar Ror, A. Aryan, J. -M. Bai, M. A. Castro-Tirado, Y. -F. Fan, E. Fernández-García, A. Kumar, A. Lindanger, A. Mezentsev, J. Navarro-González, T. Neubert, N. Østgaard, I. Pérez-García, V. Reglero, D. Sarria, T. R. Sun, D. -R. Xiong, J. Yang, Y. -H. Yang, B. -B. Zhang. 2022-05-16. Multi-wavelength study of the luminous GRB 210619B observed with Fermi and ASIM. https://doi.org/10.1093/mnras%2Fstac3629

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