GRB$\,$220831A: a hostless, intermediate Gamma-ray burst with an unusual optical afterglow
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2024
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| author | Freeburn, James O'Connor, Brendan Cooke, Jeff Dobie, Dougal Möller, Anais Tejos, Nicolas Zhang, Jielai Beniamini, Paz Auchettl, Katie DeLaunay, James Dichiara, Simone Fong, Wen-fai Goode, Simon Gordon, Alexa Kilpatrick, Charles D. Lien, Amy Mihalenko, Cassidy Ryan, Geoffrey Siellez, Karelle Suhr, Mark Troja, Eleonora Van Bemmel, Natasha Webb, Sara |
| author_facet | Freeburn, James O'Connor, Brendan Cooke, Jeff Dobie, Dougal Möller, Anais Tejos, Nicolas Zhang, Jielai Beniamini, Paz Auchettl, Katie DeLaunay, James Dichiara, Simone Fong, Wen-fai Goode, Simon Gordon, Alexa Kilpatrick, Charles D. Lien, Amy Mihalenko, Cassidy Ryan, Geoffrey Siellez, Karelle Suhr, Mark Troja, Eleonora Van Bemmel, Natasha Webb, Sara |
| contents | GRB$\,$220831A is a gamma-ray burst (GRB) with a duration and spectral peak energy that places it at the interface between the distribution of long-soft and short-hard GRBs. In this paper, we present the multi-wavelength follow-up campaign to GRB$\,$220831A and its optical, near-infrared, X-ray and radio counterparts. Our deep optical and near-infrared observations do not reveal an underlying host galaxy, and establish that GRB$\,$220831A is observationally hostless to depth, $m_i\gtrsim26.6$ AB mag. Based on the Amati relation and the non-detection of an accompanying supernova, we find that this GRB is most likely to have originated from a collapsar at $z>2$, but it could also possibly be a compact object merger at $z<0.4$ with a large separation distance from its host galaxy. Regardless of its origin, we show that its optical and near-infrared counterpart departs from the evolution expected from a forward shock dominated synchrotron afterglow, exhibiting a steep post-break temporal powerlaw index of $-3.83^{+0.62}_{-0.79}$, too steep to be the jet-break. By analysing a range of models, we find that the observed steep departure from forward shock closure relations is likely due to an internal process producing either a flare or a plateau. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2411_14749 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | GRB$\,$220831A: a hostless, intermediate Gamma-ray burst with an unusual optical afterglow Freeburn, James O'Connor, Brendan Cooke, Jeff Dobie, Dougal Möller, Anais Tejos, Nicolas Zhang, Jielai Beniamini, Paz Auchettl, Katie DeLaunay, James Dichiara, Simone Fong, Wen-fai Goode, Simon Gordon, Alexa Kilpatrick, Charles D. Lien, Amy Mihalenko, Cassidy Ryan, Geoffrey Siellez, Karelle Suhr, Mark Troja, Eleonora Van Bemmel, Natasha Webb, Sara High Energy Astrophysical Phenomena GRB$\,$220831A is a gamma-ray burst (GRB) with a duration and spectral peak energy that places it at the interface between the distribution of long-soft and short-hard GRBs. In this paper, we present the multi-wavelength follow-up campaign to GRB$\,$220831A and its optical, near-infrared, X-ray and radio counterparts. Our deep optical and near-infrared observations do not reveal an underlying host galaxy, and establish that GRB$\,$220831A is observationally hostless to depth, $m_i\gtrsim26.6$ AB mag. Based on the Amati relation and the non-detection of an accompanying supernova, we find that this GRB is most likely to have originated from a collapsar at $z>2$, but it could also possibly be a compact object merger at $z<0.4$ with a large separation distance from its host galaxy. Regardless of its origin, we show that its optical and near-infrared counterpart departs from the evolution expected from a forward shock dominated synchrotron afterglow, exhibiting a steep post-break temporal powerlaw index of $-3.83^{+0.62}_{-0.79}$, too steep to be the jet-break. By analysing a range of models, we find that the observed steep departure from forward shock closure relations is likely due to an internal process producing either a flare or a plateau. |
| title | GRB$\,$220831A: a hostless, intermediate Gamma-ray burst with an unusual optical afterglow |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2411.14749 |