GRB 260310A / SN 2026fgk: A Multi-Wavelength Study of a Nearby Underluminous Long GRB and SN with a Complex Afterglow
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| Formato: | Preprint |
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2026
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| author | Gill, Ramandeep Becerra, Rosa L. Postigo, Antonio de Ugarte Thöne, Christina C. Watson, Alan M. Globus, Noémie Ducoin, Jean-Grégoire Veres, Peter Kurtz, Stanley E. Kuwata, Asuka Martín-Carrillo, Antonio Izzo, Luca Adami, Christophe Méndez, Enrique Moreno Mandarakas, Nikos Angulo-Valdez, Camila Basa, Stéphane Lee, William H. Aguilar-Ruiz, Edilberto Akl, Dalya Aller, Margo F. Aloy, Miguel Ángel An, Jie Antier, Sarah Atteia, Jean-Luc Butler, Nathaniel R. Chanchaiworawit, Krittapas De La Parra, Philipe V. Dornic, Damien Fortin, Francis Fu, Shaoyu Fynbo, Johan P. U. Galbany, Lluis García-García, Leonardo Geier, Stefan Guelfand, Marion He, Linbo Jiang, Shuaiqing Floc'h, Emeric Le Lincetto, Massimiliano Liu, Xing Lombardi, Gianluca López-Cámara, Diego Malesani, Daniele Bjørn Magnani, Francesco Noysena, Kanthanakorn Pereyra, Margarita Rakotondrainibe, Ny Avo Readhead, Anthony C. S. Russeil, Delphine Sánchez-Álvarez, Fredd Schneider, Benjamin Surti, Tirth D. Tanvir, Nial R. Tinyanont, Samaporn Xu, Dong Zhu, Zipei |
| author_facet | Gill, Ramandeep Becerra, Rosa L. Postigo, Antonio de Ugarte Thöne, Christina C. Watson, Alan M. Globus, Noémie Ducoin, Jean-Grégoire Veres, Peter Kurtz, Stanley E. Kuwata, Asuka Martín-Carrillo, Antonio Izzo, Luca Adami, Christophe Méndez, Enrique Moreno Mandarakas, Nikos Angulo-Valdez, Camila Basa, Stéphane Lee, William H. Aguilar-Ruiz, Edilberto Akl, Dalya Aller, Margo F. Aloy, Miguel Ángel An, Jie Antier, Sarah Atteia, Jean-Luc Butler, Nathaniel R. Chanchaiworawit, Krittapas De La Parra, Philipe V. Dornic, Damien Fortin, Francis Fu, Shaoyu Fynbo, Johan P. U. Galbany, Lluis García-García, Leonardo Geier, Stefan Guelfand, Marion He, Linbo Jiang, Shuaiqing Floc'h, Emeric Le Lincetto, Massimiliano Liu, Xing Lombardi, Gianluca López-Cámara, Diego Malesani, Daniele Bjørn Magnani, Francesco Noysena, Kanthanakorn Pereyra, Margarita Rakotondrainibe, Ny Avo Readhead, Anthony C. S. Russeil, Delphine Sánchez-Álvarez, Fredd Schneider, Benjamin Surti, Tirth D. Tanvir, Nial R. Tinyanont, Samaporn Xu, Dong Zhu, Zipei |
| contents | We present a comprehensive multi-wavelength study of GRB 260310A / SN 2026fgk, a nearby ($z=0.153$), long-duration gamma-ray burst (GRB) with an exceptionally underluminous prompt $γ$-ray emission and a Comptonized spectrum. It is located at the edge of a blue host galaxy with a projected distance of 15 kpc, which is one of the largest offsets reported for a long GRB. The bright optical afterglow, with dense coverage from COLIBRÍ, likely peaked at a few to several hours post-burst, followed by a shallow decay not expected from canonical afterglow models. Both the optical and X-ray light curves show a brief chromatic plateau from $4-7$ days and a more standard decay thereafter only terminated with a rebrightening at $\sim20$ days. We demonstrate that this feature is best described by a combination of emission from the Ic-BL supernova, as identified in GTC spectra, and a late-time refreshed shock. The broadband optical to X-ray spectral energy distribution is well described by synchrotron emission from the forward shock, while the radio observations demand an additional emission component. We model the afterglow using (a) an on-axis uniform jet from a dirty fireball with late-time energy injection and (b) a misaligned jet with power-law angular structure, both having material emitting along our line-of-sight (LOS) moving with an initial Lorentz factor of $Γ_0\sim20-35$. Had this GRB occurred at a more typical redshift ($z\gtrsim0.5$), its prompt emission would likely have remained undetected by current $γ$-ray monitors while its optical afterglow would still have been readily detectable, placing it observationally among orphan afterglows or gamma-ray quiet fast X-ray transients. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_26091 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | GRB 260310A / SN 2026fgk: A Multi-Wavelength Study of a Nearby Underluminous Long GRB and SN with a Complex Afterglow Gill, Ramandeep Becerra, Rosa L. Postigo, Antonio de Ugarte Thöne, Christina C. Watson, Alan M. Globus, Noémie Ducoin, Jean-Grégoire Veres, Peter Kurtz, Stanley E. Kuwata, Asuka Martín-Carrillo, Antonio Izzo, Luca Adami, Christophe Méndez, Enrique Moreno Mandarakas, Nikos Angulo-Valdez, Camila Basa, Stéphane Lee, William H. Aguilar-Ruiz, Edilberto Akl, Dalya Aller, Margo F. Aloy, Miguel Ángel An, Jie Antier, Sarah Atteia, Jean-Luc Butler, Nathaniel R. Chanchaiworawit, Krittapas De La Parra, Philipe V. Dornic, Damien Fortin, Francis Fu, Shaoyu Fynbo, Johan P. U. Galbany, Lluis García-García, Leonardo Geier, Stefan Guelfand, Marion He, Linbo Jiang, Shuaiqing Floc'h, Emeric Le Lincetto, Massimiliano Liu, Xing Lombardi, Gianluca López-Cámara, Diego Malesani, Daniele Bjørn Magnani, Francesco Noysena, Kanthanakorn Pereyra, Margarita Rakotondrainibe, Ny Avo Readhead, Anthony C. S. Russeil, Delphine Sánchez-Álvarez, Fredd Schneider, Benjamin Surti, Tirth D. Tanvir, Nial R. Tinyanont, Samaporn Xu, Dong Zhu, Zipei High Energy Astrophysical Phenomena We present a comprehensive multi-wavelength study of GRB 260310A / SN 2026fgk, a nearby ($z=0.153$), long-duration gamma-ray burst (GRB) with an exceptionally underluminous prompt $γ$-ray emission and a Comptonized spectrum. It is located at the edge of a blue host galaxy with a projected distance of 15 kpc, which is one of the largest offsets reported for a long GRB. The bright optical afterglow, with dense coverage from COLIBRÍ, likely peaked at a few to several hours post-burst, followed by a shallow decay not expected from canonical afterglow models. Both the optical and X-ray light curves show a brief chromatic plateau from $4-7$ days and a more standard decay thereafter only terminated with a rebrightening at $\sim20$ days. We demonstrate that this feature is best described by a combination of emission from the Ic-BL supernova, as identified in GTC spectra, and a late-time refreshed shock. The broadband optical to X-ray spectral energy distribution is well described by synchrotron emission from the forward shock, while the radio observations demand an additional emission component. We model the afterglow using (a) an on-axis uniform jet from a dirty fireball with late-time energy injection and (b) a misaligned jet with power-law angular structure, both having material emitting along our line-of-sight (LOS) moving with an initial Lorentz factor of $Γ_0\sim20-35$. Had this GRB occurred at a more typical redshift ($z\gtrsim0.5$), its prompt emission would likely have remained undetected by current $γ$-ray monitors while its optical afterglow would still have been readily detectable, placing it observationally among orphan afterglows or gamma-ray quiet fast X-ray transients. |
| title | GRB 260310A / SN 2026fgk: A Multi-Wavelength Study of a Nearby Underluminous Long GRB and SN with a Complex Afterglow |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2605.26091 |