The radio afterglow of the ultra-long GRB 220627A
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2025
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| author | Leung, James K. Salafia, Om Sharan Spingola, Cristiana Ghirlanda, Giancarlo Giarratana, Stefano Giroletti, Marcello Reynolds, Cormac Wang, Ziteng An, Tao Deller, Adam Drout, Maria R. Kaplan, David L. Lenc, Emil Murphy, Tara Perez-Torres, Miguel Rhodes, Lauren |
| author_facet | Leung, James K. Salafia, Om Sharan Spingola, Cristiana Ghirlanda, Giancarlo Giarratana, Stefano Giroletti, Marcello Reynolds, Cormac Wang, Ziteng An, Tao Deller, Adam Drout, Maria R. Kaplan, David L. Lenc, Emil Murphy, Tara Perez-Torres, Miguel Rhodes, Lauren |
| contents | We present the discovery of the radio afterglow of the most distant ultra-long gamma-ray burst (GRB) detected to date, GRB~220627A at redshift $z=3.084$. Its prompt gamma-ray light curve shows a double-pulse profile, with the pulses separated by a period of quiescence lasting ${\sim} 15$\,min, leading to early speculation it could be a strongly gravitationally lensed GRB. However, our analysis of the \textit{Fermi}/GBM spectra taken during the time intervals of both pulses show clear differences in their spectral energy distributions, disfavouring the lensing scenario. We observed the radio afterglow from 7 to 456\,d post-burst: an initial, steep decay ($F_ν \propto t^{-2}$) is followed by a shallower decline ($F_ν \propto t^{-1/2}$) after ${\sim} 20$\,d. There are three scenarios that could explain these radio properties: (i) energy injection from an additional, slower ejecta component catching up to the external shock; (ii) a stratified density profile going as $n \propto r^{-8/3}$; or alternatively, (iii) the presence of a slow, wide ejecta component in addition to a fast, narrow ejecta component. We also conducted an independent test of the lensing hypothesis via Very Long Baseline Interferometry (VLBI) observations at ${\sim} 12$\,d post-burst by searching, for the first time, for multiple images of the candidate lensed GRB afterglow. Our experiment highlighted the growing need for developments in real-time correlation capabilities for time-critical VLBI experiments, particularly as we advance towards the SKA and ngVLA era of radio astronomy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_13435 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The radio afterglow of the ultra-long GRB 220627A Leung, James K. Salafia, Om Sharan Spingola, Cristiana Ghirlanda, Giancarlo Giarratana, Stefano Giroletti, Marcello Reynolds, Cormac Wang, Ziteng An, Tao Deller, Adam Drout, Maria R. Kaplan, David L. Lenc, Emil Murphy, Tara Perez-Torres, Miguel Rhodes, Lauren High Energy Astrophysical Phenomena We present the discovery of the radio afterglow of the most distant ultra-long gamma-ray burst (GRB) detected to date, GRB~220627A at redshift $z=3.084$. Its prompt gamma-ray light curve shows a double-pulse profile, with the pulses separated by a period of quiescence lasting ${\sim} 15$\,min, leading to early speculation it could be a strongly gravitationally lensed GRB. However, our analysis of the \textit{Fermi}/GBM spectra taken during the time intervals of both pulses show clear differences in their spectral energy distributions, disfavouring the lensing scenario. We observed the radio afterglow from 7 to 456\,d post-burst: an initial, steep decay ($F_ν \propto t^{-2}$) is followed by a shallower decline ($F_ν \propto t^{-1/2}$) after ${\sim} 20$\,d. There are three scenarios that could explain these radio properties: (i) energy injection from an additional, slower ejecta component catching up to the external shock; (ii) a stratified density profile going as $n \propto r^{-8/3}$; or alternatively, (iii) the presence of a slow, wide ejecta component in addition to a fast, narrow ejecta component. We also conducted an independent test of the lensing hypothesis via Very Long Baseline Interferometry (VLBI) observations at ${\sim} 12$\,d post-burst by searching, for the first time, for multiple images of the candidate lensed GRB afterglow. Our experiment highlighted the growing need for developments in real-time correlation capabilities for time-critical VLBI experiments, particularly as we advance towards the SKA and ngVLA era of radio astronomy. |
| title | The radio afterglow of the ultra-long GRB 220627A |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2502.13435 |