Rapid radio brightening of GRB 210702A

Anderson, Gemma; Russell, T. D.; Bahramian, A.; Wijers, R. A. M. J.; Ryder, S. D.; Fausey, H. M.; Miller-Jones, J. C. A.; Zhu, S. J.; Wagner, S. J.; Hancock, P. J.; Goodwin, A. J.; Galvin, T. J.; Rowlinson, A.; Bell, M. E.; Schussler, F.; Rowell, G.; Sammons, M. W.; van der Horst, A. J.; Konno, R.

doi:10.1093/mnras/stad1635

Journal Article

PUBDB-2023-03986

Rapid radio brightening of GRB 210702A

Anderson, G. (Corresponding author) ; Russell, T. D. ; Fausey, H. M. ; van der Horst, A. J. ; Hancock, P. J. ; Bahramian, A. ; Bell, M. E. ; Miller-Jones, J. C. A. ; Rowell, G. ; Sammons, M. W. ; Wijers, R. A. M. J. ; Galvin, T. J. ; Goodwin, A. J. ; Konno, R.Extern*DESY* ; Rowlinson, A. ; Ryder, S. D. ; Schussler, F. ; Wagner, S. J. ; Zhu, S. J.DESY*

2023
Oxford Univ. Press Oxford

Monthly notices of the Royal Astronomical Society 523(4), 4992 - 5005 (2023) [10.1093/mnras/stad1635]

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Please use a persistent id in citations: doi:10.1093/mnras/stad1635

Report No.: arXiv:2211.11212

Abstract: We observed the rapid radio brightening of GRB 210702A with the Australian Telescope Compact Array (ATCA) just 11hr post-burst, tracking early-time radio variability over a 5hr period on ~15min timescales at 9.0, 16.7, and 21.2GHz. A broken power-law fit to the 9.0GHz light curve showed that the 5hr flare peaked at a flux density of 0.4+/-0.1mJy at ~13hr post-burst with a steep rise and decline. The observed temporal and spectral evolution are not expected in the standard internal-external shock model, where forward and reverse shock radio emission evolves on much longer timescales. The early-time (<1day) optical and X-ray light curves from the Neil Gehrels Swift Observatory demonstrated typical afterglow forward shock behaviour, allowing us to use blast wave physics to determine a likely homogeneous circumburst medium and an emitting electron population power-law index of p=2.9+/-0.1. We suggest the early-time radio flare is likely due to weak interstellar scintillation (ISS), which boosted the radio afterglow emission above the ATCA sensitivity limit on minute timescales. Using weak ISS relations, we were able to place an upper limit on the size of the blast wave of $\leq6 \times 10^{16}$cm in the plane of the sky, which is consistent with the theoretical forward shock size prediction of $8\times10^{16}$cm for GRB 210702A at ~13h post-burst. This represents the earliest ISS size constraint on a GRB blast wave to date, demonstrating the importance of rapid (<1day) radio follow-up of GRBs using several-hour integrations to capture the early afterglow evolution, and to track scintillation over a broad frequency range.

Classification:

ddc:520

Note: Submitted to MNRAS 13 pages, 6 figures, 2 tables Waiting for fulltext

Contributing Institute(s):

High Energy Steroscopic System (ZEU-HESS)

Research Program(s):

613 - Matter and Radiation from the Universe (POF4-613) (POF4-613)

Experiment(s):

High Energy Stereoscopic System

Appears in the scientific report 2023

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Medline

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