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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2510.19132 |
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| _version_ | 1866912910141292544 |
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| author | Angulo-Valdez, Camila Becerra, Rosa L. Gill, Ramandeep Globus, Noémie Lee, William H. López-Cámara, Diego Mihalenko, Cassidy Moreno-Méndez, Enrique Ricci, Roberto Siellez, Karelle Watson, Alan M. Yadav, Muskan Yang, Yu-han Akl, Dalya Antier, Sarah Atteia, Jean-Luc Basa, Stéphane Butler, Nathaniel R. Dichiara, Simone Dornic, Damien Ducoin, Jean-Grégoire Fortin, Francis García-García, Leonardo López, Kin Ocelotl Magnani, Francesco O'Connor, Brendan Pereyra, Margarita Rakotondrainibe, Ny Avo Sánchez-Álvarez, Fredd Schneider, Benjamin Troja, Eleonora Postigo, Antonio de Ugarte |
| author_facet | Angulo-Valdez, Camila Becerra, Rosa L. Gill, Ramandeep Globus, Noémie Lee, William H. López-Cámara, Diego Mihalenko, Cassidy Moreno-Méndez, Enrique Ricci, Roberto Siellez, Karelle Watson, Alan M. Yadav, Muskan Yang, Yu-han Akl, Dalya Antier, Sarah Atteia, Jean-Luc Basa, Stéphane Butler, Nathaniel R. Dichiara, Simone Dornic, Damien Ducoin, Jean-Grégoire Fortin, Francis García-García, Leonardo López, Kin Ocelotl Magnani, Francesco O'Connor, Brendan Pereyra, Margarita Rakotondrainibe, Ny Avo Sánchez-Álvarez, Fredd Schneider, Benjamin Troja, Eleonora Postigo, Antonio de Ugarte |
| contents | We present the photometric and spectroscopic analysis of the short-duration GRB 250221A ($T_{90}=1.80\pm0.32$ s), using a data set from the optical facilities COLIBRÍ, the Harlingten 50~cm Telescope, and the Very Large Telescope. We complement these observations with data from the Neil Gehrels Swift Observatory and the Einstein Probe, as well as radio observations from the Very Large Array. GRB 250221A is among the few short GRBs with direct afterglow spectroscopy, which gives a secure redshift determination of $z=0.768$ and allows the unambiguous identification of the host as a galaxy with a star-formation rate of $\sim3\,M_\odot\,{\rm yr}^{-1}$. The X-ray and optical light curves up to $T_0+3\times 10^4$ s (where $T_0$ refers to the GRB trigger time) are well described by forward-shock synchrotron emission in the slow-cooling regime within the standard fireball framework. However, at $T_0 \sim 5\times 10^4$ s, both the X-ray and optical bands exhibit an excess over the same interval, which we interpret as evidence of energy injection into a jet with a half-opening angle of $θ_j=11.5^{\circ}$ through a refreshed shock powered by late central engine activity or a radially stratified ejecta. The burst properties (duration, spectral hardness, peak energy, and location in the Amati plane) all favour a compact binary merger origin. However, our modelling of the afterglow suggests a dense circumburst medium ($n\sim80$ cm$^{-3}$), which is more typical of a collapsar environment. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_19132 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Evidence of Energy Injection in the Short and Distant GRB 250221A in a High Density Environment Angulo-Valdez, Camila Becerra, Rosa L. Gill, Ramandeep Globus, Noémie Lee, William H. López-Cámara, Diego Mihalenko, Cassidy Moreno-Méndez, Enrique Ricci, Roberto Siellez, Karelle Watson, Alan M. Yadav, Muskan Yang, Yu-han Akl, Dalya Antier, Sarah Atteia, Jean-Luc Basa, Stéphane Butler, Nathaniel R. Dichiara, Simone Dornic, Damien Ducoin, Jean-Grégoire Fortin, Francis García-García, Leonardo López, Kin Ocelotl Magnani, Francesco O'Connor, Brendan Pereyra, Margarita Rakotondrainibe, Ny Avo Sánchez-Álvarez, Fredd Schneider, Benjamin Troja, Eleonora Postigo, Antonio de Ugarte High Energy Astrophysical Phenomena We present the photometric and spectroscopic analysis of the short-duration GRB 250221A ($T_{90}=1.80\pm0.32$ s), using a data set from the optical facilities COLIBRÍ, the Harlingten 50~cm Telescope, and the Very Large Telescope. We complement these observations with data from the Neil Gehrels Swift Observatory and the Einstein Probe, as well as radio observations from the Very Large Array. GRB 250221A is among the few short GRBs with direct afterglow spectroscopy, which gives a secure redshift determination of $z=0.768$ and allows the unambiguous identification of the host as a galaxy with a star-formation rate of $\sim3\,M_\odot\,{\rm yr}^{-1}$. The X-ray and optical light curves up to $T_0+3\times 10^4$ s (where $T_0$ refers to the GRB trigger time) are well described by forward-shock synchrotron emission in the slow-cooling regime within the standard fireball framework. However, at $T_0 \sim 5\times 10^4$ s, both the X-ray and optical bands exhibit an excess over the same interval, which we interpret as evidence of energy injection into a jet with a half-opening angle of $θ_j=11.5^{\circ}$ through a refreshed shock powered by late central engine activity or a radially stratified ejecta. The burst properties (duration, spectral hardness, peak energy, and location in the Amati plane) all favour a compact binary merger origin. However, our modelling of the afterglow suggests a dense circumburst medium ($n\sim80$ cm$^{-3}$), which is more typical of a collapsar environment. |
| title | Evidence of Energy Injection in the Short and Distant GRB 250221A in a High Density Environment |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2510.19132 |