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| Auteurs principaux: | , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2025
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| Accès en ligne: | https://arxiv.org/abs/2511.07529 |
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| author | Bose, Subhash Stritzinger, M. D. Malmgaard, A. Miller, C. J. Elias-Rosa, N. Fynbo, J. P. U. Ashall, C. Burns, C. R. DerKacy, J. M. Galbany, L. Gutiérrez, C. P. Hoogendam, W. B. Hsiao, E. Y. Jensen, E. A. M. Medler, K. Alburai, Alaa Anderson, J. Baron, E. Duarte, J. Gromadzki, M. Inserra, C. Mazzali, P. A. Müller-Bravo, T. E. Lundqvist, P. Reguitti, A. Salmaso, I. Sand, D. J. Valerin, G. |
| author_facet | Bose, Subhash Stritzinger, M. D. Malmgaard, A. Miller, C. J. Elias-Rosa, N. Fynbo, J. P. U. Ashall, C. Burns, C. R. DerKacy, J. M. Galbany, L. Gutiérrez, C. P. Hoogendam, W. B. Hsiao, E. Y. Jensen, E. A. M. Medler, K. Alburai, Alaa Anderson, J. Baron, E. Duarte, J. Gromadzki, M. Inserra, C. Mazzali, P. A. Müller-Bravo, T. E. Lundqvist, P. Reguitti, A. Salmaso, I. Sand, D. J. Valerin, G. |
| contents | We report observations of Type Ia SN 2021hem, located in an apparently hostless environment. With a peak absolute B-band magnitude of -19.96 mag, and a lack of secondary maximum in near-infrared and i-band light curves make it resemble 2003fg-like events. The slowly evolving light curves, and the earliest spectrum showing CII absorption lines, further support this classification. Fireball model fit to early light curves yields a time of first light of -16.43 days relative to B-band maximum. The first detection occurs 1.51 days before the onset of the fireball-like flux rise. This early emission, and $(g - r)_0$ color, is inconsistent with circumstellar or companion interaction. Instead, shallow $^{56}$Ni mixing or an asymmetric $^{56}$Ni distribution offers a plausible explanation. SN2021hem is the fifth known 2003fg-like SN with early-time excess flux emission. The estimated mass of radioactive $^{56}$Ni in SN2021hem is $1.00\pm0.09 M_\odot$. Deep GTC imaging obtained 2.5 yr after the explosion (with $m_{lim,r}=24.4$ mag and $μ_{lim,r} = 26.3\rm~mag~arsec^{-2}$), reveals no coincident host, thereby ruling out most faint dwarf and UDGs. Alternatively, assuming the nearest plausible AGN host galaxy, at a distance of 104 kpc, implies a hyper-velocity progenitor ejected at $\sim$2200 km/s by AGN interaction. A faint diffuse feature ~6 kpc from the SN site has also been detected in the image, with its surface brightness of a UDGs. However, it is unclear whether it is a galaxy and is associated with SN2021hem. Considering its large normalized directional light distance ($d_{DLR}\sim3-4$) from SN, and its unusual elongation, it is a candidate of low probability to be the host galaxy of SN2021hem. These results identify SN2021hem as one of the strongest candidates for a hostless SN Ia, underscoring the diversity of luminous, slowly evolving, 2003fg-like explosions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_07529 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Type Ia Supernova 2021hem: A 2003fg-like Event in an Apparently Hostless Environment Bose, Subhash Stritzinger, M. D. Malmgaard, A. Miller, C. J. Elias-Rosa, N. Fynbo, J. P. U. Ashall, C. Burns, C. R. DerKacy, J. M. Galbany, L. Gutiérrez, C. P. Hoogendam, W. B. Hsiao, E. Y. Jensen, E. A. M. Medler, K. Alburai, Alaa Anderson, J. Baron, E. Duarte, J. Gromadzki, M. Inserra, C. Mazzali, P. A. Müller-Bravo, T. E. Lundqvist, P. Reguitti, A. Salmaso, I. Sand, D. J. Valerin, G. High Energy Astrophysical Phenomena We report observations of Type Ia SN 2021hem, located in an apparently hostless environment. With a peak absolute B-band magnitude of -19.96 mag, and a lack of secondary maximum in near-infrared and i-band light curves make it resemble 2003fg-like events. The slowly evolving light curves, and the earliest spectrum showing CII absorption lines, further support this classification. Fireball model fit to early light curves yields a time of first light of -16.43 days relative to B-band maximum. The first detection occurs 1.51 days before the onset of the fireball-like flux rise. This early emission, and $(g - r)_0$ color, is inconsistent with circumstellar or companion interaction. Instead, shallow $^{56}$Ni mixing or an asymmetric $^{56}$Ni distribution offers a plausible explanation. SN2021hem is the fifth known 2003fg-like SN with early-time excess flux emission. The estimated mass of radioactive $^{56}$Ni in SN2021hem is $1.00\pm0.09 M_\odot$. Deep GTC imaging obtained 2.5 yr after the explosion (with $m_{lim,r}=24.4$ mag and $μ_{lim,r} = 26.3\rm~mag~arsec^{-2}$), reveals no coincident host, thereby ruling out most faint dwarf and UDGs. Alternatively, assuming the nearest plausible AGN host galaxy, at a distance of 104 kpc, implies a hyper-velocity progenitor ejected at $\sim$2200 km/s by AGN interaction. A faint diffuse feature ~6 kpc from the SN site has also been detected in the image, with its surface brightness of a UDGs. However, it is unclear whether it is a galaxy and is associated with SN2021hem. Considering its large normalized directional light distance ($d_{DLR}\sim3-4$) from SN, and its unusual elongation, it is a candidate of low probability to be the host galaxy of SN2021hem. These results identify SN2021hem as one of the strongest candidates for a hostless SN Ia, underscoring the diversity of luminous, slowly evolving, 2003fg-like explosions. |
| title | The Type Ia Supernova 2021hem: A 2003fg-like Event in an Apparently Hostless Environment |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2511.07529 |