Details

Autor(en) / Beteiligte

• 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

Titel

Rapid radio brightening of GRB 210702A

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2023-06, Vol.523 (4), p.4992-5005

Ort / Verlag

Oxford University Press

Erscheinungsjahr

2023

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• 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.