Multiwavelength study of the luminous GRB 210619B observed with Fermi and ASIM

• Published in: Monthly notices of the Royal Astronomical Society Vol. 519; no. 3; pp. 3201 - 3226
• Main Authors: Caballero-García, M D, Gupta, Rahul, Pandey, S B, Oates, S R, Marisaldi, M, Ramsli, A, Hu, Y-D, Castro-Tirado, A J, Sánchez-Ramírez, R, Connell, P H, Christiansen, F, Ror, A Kumar, Aryan, A, Bai, J-M, Castro-Tirado, M A, Fan, Y-F, Fernández-García, E, Kumar, A, Lindanger, A, Mezentsev, A, Navarro-González, J, Neubert, T, Østgaard, N, Pérez-García, I, Reglero, V, Sarria, D, Sun, T R, Xiong, D-R, Yang, J, Yang, Y-H, Zhang, B-B
• Format: Journal Article
• Language: English
• Published: Oxford University Press 09-01-2023
• Subjects: methods: data analysis; gamma-ray burst: general; gamma-ray burst: individual: GRB 210619B
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stac3629

ABSTRACT
We report on detailed multiwavelength observations and analysis of the very bright and long GRB 210619B, detected by the Atmosphere-Space Interactions Monitor installed on the International Space Station 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 index (αpt) 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 αpt exhibit the flux tracking pattern. The late time broad-band photometric data set can be explained within the framework of the external forward shock model with νm < νc < νx (where νm, νc, and νx 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 ± 0.01 mag for the small magellanic cloud extinction law. In addition, we also report late-time optical observations with the 10.4 m Gran Telescopio de Canarias placing deep upper limits for the host galaxy (z = 1.937), favouring a faint, dwarf host for the burst.