| Title: |
The Type Ia supernova 2021hem: A 2003fg-like event in an apparently hostless environment |
| Authors: |
Bose, S.; 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, A.; Anderson, J.; Baron, E.; Duarte, J.; Gromadzki, M.; Inserra, Cosimo |
| Publisher Information: |
EDP Sciences |
| Publication Year: |
2026 |
| Collection: |
Cardiff University: ORCA (Online Research @ Cardiff) |
| Description: |
We report observations of a Type Ia supernova (SN Ia) 2021hem that was discovered within 48 hours of last nondetection and is located in an apparently hostless environment. With a peak absolute B -band magnitude of M B , max = −19.96 ± 0.29 mag, SN 2021hem lies at the luminous end of the SNe Ia distribution. Its near-infrared and i -band light curves lack the secondary maximum, which is otherwise ubiquitous to normal and 1991T-like SNe Ia. Instead, these properties cause SN 2021hem to closely resemble 2003fg-like events. The slowly evolving light curves (characterized by Δ m 15 ( B ) = 1.02 ± 0.02 mag; s BV = 0.94 ± 0.05) and the earliest spectrum showing C II λ 6580 and λ 7235 absorption lines further support this classification. Other spectroscopic features, including Si II line diagnostics, resemble those of normal SNe Ia. A fit of a fireball model to the early-time light curves yields a time of first light of t first = −16.43 +0.45 −0.38 days relative to B -band maximum. The first photometric detection occurs 1.51 +0.45 −0.38 days before the onset of fireball-like flux rise. This early emission, together with the intrinsic ( 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 for the delayed onset of the fireball flux rise, while a double-detonation scenario with a thin helium shell remains a less likely alternative. Notably, SN 2021hem represents the fifth known 2003fg-like SN that has early-time activity or excess flux emission. The estimated mass of radioactive 56 Ni synthesized in SN 2021hem is 1.00 ± 0.09 M ⊙ . Deep GTC imaging obtained 2.5 years after the explosion, with an estimated limiting magnitude of m lim, r = 24.4 mag and a surface-brightness limit of μ lim, r = 26.3 mag arcsec −2 , revealed no coincident host. Most faint dwarf and ultradiffuse galaxies (UDGs) are therefore ruled out. Alternatively, if the nearest plausible AGN host galaxy located at a projected distance of ... |
| Document Type: |
article in journal/newspaper |
| File Description: |
application/pdf |
| Language: |
English |
| Relation: |
https://orca.cardiff.ac.uk/id/eprint/185267/1/aa58053-25.pdf; Bose, S., 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, A., Anderson, J., Baron, E., Duarte, J., Gromadzki, M. and Inserra, Cosimo https://orca.cardiff.ac.uk/view/cardiffauthors/A2408324G.html orcid:0000-0002-3968-4409 orcid:0000-0002-3968-4409 2026. The Type Ia supernova 2021hem: A 2003fg-like event in an apparently hostless environment. Astronomy & Astrophysics 706 , A252. 10.1051/0004-6361/202558053 https://doi.org/10.1051/0004-6361%2F202558053 file https://orca.cardiff.ac.uk/id/eprint/185267/1/aa58053-25.pdf |
| DOI: |
10.1051/0004-6361/202558053 |
| Availability: |
https://orca.cardiff.ac.uk/id/eprint/185267/; https://doi.org/10.1051/0004-6361/202558053 |
| Rights: |
cc_by_4_0 |
| Accession Number: |
edsbas.78789392 |
| Database: |
BASE |