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https://hdl.handle.net/2440/139418
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Type: | Journal article |
Title: | Rapid radio brightening of GRB 210702A |
Author: | Anderson, G.E. 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. Rowlinson, A. Ryder, S.D. Schüssler, F. Wagner, S.J. Zhu, S.J. |
Citation: | Monthly Notices of the Royal Astronomical Society, 2023; 523(4):4992-5005 |
Publisher: | Oxford University Press (OUP) |
Issue Date: | 2023 |
ISSN: | 0035-8711 1365-2966 |
Statement of Responsibility: | G. E. Anderson, T. D. Russell, H. M. Fausey, A. J. van der Horst, P. J. Hancock, A. Bahramian, M. E. Bell, J. C. A. Miller-Jones, G. Rowell, M. W. Sammons, R. A. M. J. Wijers, T. J. Galvin, A. J. Goodwin, R. Konno, A. Rowlinson, S. D. Ryder, F. Schussler, S. J. Wagner, and S. J. Zhu |
Abstract: | We observed the rapid radio brightening of GRB 210702A with the Australia Telescope Compact Array (ATCA) just 11 h post-burst, tracking early-time radio variability over a 5 h period on ∼15 min time-scales at 9.0, 16.7, and 21.2 GHz. A broken power law fit to the 9.0 GHz light curve showed that the 5 h flare peaked at a flux density of 0.4 ± 0.1 mJy at ∼13 h post-burst. The observed temporal and spectral evolution is not expected in the standard internal–external shock model, where forward and reverse shock radio emission evolves on much longer time-scales. The early-time (<1 d) 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 that 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 time-scales. Using relations for ISS in the weak regime, we were able to place an upper limit on the size of the blast wave of ≲6 × 1016 cm in the plane of the sky, which is consistent with the theoretical forward shock size prediction of 8 × 1016 cm for GRB 210702A at ∼13 h post-burst. This represents the earliest ISS size constraint on a gamma-ray burst (GRB) blast wave to date, demonstrating the importance of rapid (<1 d) radio follow-up of GRBs using several-hour integrations to capture the early afterglow evolution and to track the scintillation over a broad frequency range. |
Keywords: | gamma-ray bursts; individual; GRB 210702A; radio continuum; transients |
Rights: | © 2023 The Author(s) |
DOI: | 10.1093/mnras/stad1635 |
Grant ID: | http://purl.org/au-research/grants/arc/DE180100346 http://purl.org/au-research/grants/arc/DP200102471 |
Published version: | http://dx.doi.org/10.1093/mnras/stad1635 |
Appears in Collections: | Physics publications |
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