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...
| Main Authors: | , , , , , , , , , , , , , , , , , , |
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| Format: | Journal Article |
| Published: |
2023
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| Online Access: | http://purl.org/au-research/grants/arc/DE180100346 http://hdl.handle.net/20.500.11937/96504 |
| _version_ | 1848766160526376960 |
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| author | Anderson, Gemma E. Russell, T.D. Fausey, H.M. van der Horst, A.J. Hancock, Paul J. Bahramian, Arash Bell, M.E. Miller-Jones, James C. A. Rowell, G. Sammons, Mawson W. Wijers, R.A.M.J. Galvin, Timothy J. Goodwin, Adelle J. Konno, R. Rowlinson, A. Ryder, S.D. Schüssler, F. Wagner, S.J. Zhu, S.J. |
| author_facet | Anderson, Gemma E. Russell, T.D. Fausey, H.M. van der Horst, A.J. Hancock, Paul J. Bahramian, Arash Bell, M.E. Miller-Jones, James C. A. Rowell, G. Sammons, Mawson W. Wijers, R.A.M.J. Galvin, Timothy J. Goodwin, Adelle J. Konno, R. Rowlinson, A. Ryder, S.D. Schüssler, F. Wagner, S.J. Zhu, S.J. |
| author_sort | Anderson, Gemma E. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | 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. |
| first_indexed | 2025-11-14T11:46:44Z |
| format | Journal Article |
| id | curtin-20.500.11937-96504 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T11:46:44Z |
| publishDate | 2023 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-965042025-01-14T01:30:29Z Rapid radio brightening of GRB 210702A Anderson, Gemma E. Russell, T.D. Fausey, H.M. van der Horst, A.J. Hancock, Paul J. Bahramian, Arash Bell, M.E. Miller-Jones, James C. A. Rowell, G. Sammons, Mawson W. Wijers, R.A.M.J. Galvin, Timothy J. Goodwin, Adelle J. Konno, R. Rowlinson, A. Ryder, S.D. Schüssler, F. Wagner, S.J. Zhu, S.J. 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. 2023 Journal Article http://hdl.handle.net/20.500.11937/96504 10.1093/mnras/stad1635 http://purl.org/au-research/grants/arc/DE180100346 http://purl.org/au-research/grants/arc/DP200102471 fulltext |
| spellingShingle | Anderson, Gemma E. Russell, T.D. Fausey, H.M. van der Horst, A.J. Hancock, Paul J. Bahramian, Arash Bell, M.E. Miller-Jones, James C. A. Rowell, G. Sammons, Mawson W. Wijers, R.A.M.J. Galvin, Timothy J. Goodwin, Adelle J. Konno, R. Rowlinson, A. Ryder, S.D. Schüssler, F. Wagner, S.J. Zhu, S.J. Rapid radio brightening of GRB 210702A |
| title | Rapid radio brightening of GRB 210702A |
| title_full | Rapid radio brightening of GRB 210702A |
| title_fullStr | Rapid radio brightening of GRB 210702A |
| title_full_unstemmed | Rapid radio brightening of GRB 210702A |
| title_short | Rapid radio brightening of GRB 210702A |
| title_sort | rapid radio brightening of grb 210702a |
| url | http://purl.org/au-research/grants/arc/DE180100346 http://purl.org/au-research/grants/arc/DE180100346 http://hdl.handle.net/20.500.11937/96504 |