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Rapid radio brightening of GRB 210702A

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...

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Main Authors: Anderson, Gemma (Author) , Russell, T D (Author) , Fausey, H M (Author) , van der Horst, A J (Author) , Hancock, P J (Author) , Bahramian, A (Author) , Bell, M E (Author) , Miller-Jones, J C A (Author) , Rowell, G (Author) , Sammons, M W (Author) , Wijers, R A M J (Author) , Galvin, T J (Author) , Goodwin, A J (Author) , Konno, R (Author) , Rowlinson, A (Author) , Ryder, S D (Author) , Schüssler, F (Author) , Wagner, Stefan (Author) , Zhu, S J (Author)
Format: Article (Journal)
Language:English
Published: 2023
In: Monthly notices of the Royal Astronomical Society
Year: 2023, Volume: 523, Issue: 4, Pages: 4992-5005
ISSN:1365-2966
DOI:10.1093/mnras/stad1635
Online Access:Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1093/mnras/stad1635
Verlag, lizenzpflichtig, Volltext: https://academic.oup.com/mnras/article/523/4/4992/7190645
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Author Notes: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. Schüssler, S.J. Wagner and S.J. Zhu
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Summary: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.
Item Description:Veröffentlicht: 05. Juni 2023
Gesehen am 11.10.2023
Physical Description:Online Resource
ISSN:1365-2966
DOI:10.1093/mnras/stad1635

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