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The long-active afterglow of GRB 210204A: detection of the most delayed flares in a gamma-ray burst

Kumar, H, Gupta, R, Saraogi, D, Ahumada, T, Andreoni, I, Anupama, GC, Aryan, A, Barway, S, Bhalerao, V, Chandra, P, Coughlin, MW, Dimple, D, Dutta, A, Ghosh, A, Ho, AYQ, Kool, EC, Kumar, A, Medford, MS, Misra, K, Pandey, SB , Perley, DA, Riddle, R, Ror, AK, Setiadi, JM and Yao, Y (2022) The long-active afterglow of GRB 210204A: detection of the most delayed flares in a gamma-ray burst. Monthly Notices of the Royal Astronomical Society, 513 (2). pp. 2777-2793. ISSN 0035-8711

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We present results from extensive broadband follow-up of GRB 210204A over the period of 30 d. We detect optical flares in the afterglow at 7.6 × 105 s and 1.1 × 106 s after the burst: the most delayed flaring ever detected in a GRB afterglow. At the source redshift of 0.876, the rest-frame delay is 5.8 × 105 s (6.71 d). We investigate possible causes for this flaring and conclude that the most likely cause is a refreshed shock in the jet. The prompt emission of the GRB is within the range of typical long bursts: it shows three disjoint emission episodes, which all follow the typical GRB correlations. This suggests that GRB 210204A might not have any special properties that caused late-time flaring, and the lack of such detections for other afterglows might be resulting from the paucity of late-time observations. Systematic late-time follow-up of a larger sample of GRBs can shed more light on such afterglow behaviour. Further analysis of the GRB 210204A shows that the late-time bump in the light curve is highly unlikely due to underlying SNe at redshift (z) = 0.876 and is more likely due to the late-time flaring activity. The cause of this variability is not clearly quantifiable due to the lack of multiband data at late-time constraints by bad weather conditions. The flare of GRB 210204A is the latest flare detected to date.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
SWORD Depositor: A Symplectic
Date Deposited: 15 Nov 2022 09:15
Last Modified: 15 Nov 2022 09:15
DOI or ID number: 10.1093/mnras/stac1061
URI: https://researchonline.ljmu.ac.uk/id/eprint/18122
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