Multiwavelength View of the Close-by GRB 190829A Sheds Light on Gamma-Ray Burst Physics

Salafia, Om Sharan and Ravasio, Maria Edvige and Yang, Jun and An, Tao and Orienti, Monica and Ghirlanda, Giancarlo and Nava, Lara and Giroletti, Marcello and Mohan, Prashanth and Spinelli, Riccardo and Zhang, Yingkang and Marcote, Benito and Cimò, Giuseppe and Wu, Xuefeng and Li, Zhixuan (2022) Multiwavelength View of the Close-by GRB 190829A Sheds Light on Gamma-Ray Burst Physics. The Astrophysical Journal Letters, 931 (2). L19. ISSN 2041-8205

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Abstract

We monitored the position of the close-by (about 370 Mpc) gamma-ray burst GRB 190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the European VLBI Network and the Very Long Baseline Array, carrying out a total of nine observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of a few milliarcseconds. From a state-of-the art analysis of these data, we obtained valuable limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modeling of the multiwavelength light curves with a forward-plus-reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the HESS data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the multiwavelength, high-cadence coverage of the afterglow, inherent degeneracies in the afterglow model are broken to a large extent, allowing us to capture some unique physical insights; we find a low prompt emission efficiency of ≲10−3, a low fraction of relativistic electrons in the forward shock downstream χe < 13% (90% credible level), and a rapid decay of the magnetic field in the reverse shock downstream after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometry is not sufficiently tight as to exclude any off-axis viewing angle, but we can exclude the line of sight to have been more than ∼2° away from the border of the gamma-ray-producing region based on compactness arguments.

Item Type: Article
Subjects: STM Article > Physics and Astronomy
Depositing User: Unnamed user with email support@stmarticle.org
Date Deposited: 28 Apr 2023 05:41
Last Modified: 03 Oct 2024 04:47
URI: http://publish.journalgazett.co.in/id/eprint/1104

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