We present observations and analysis of the host-less and luminous type Ia supernova 2022ilv, illustrating it is part of the 2003fg-like family, often referred to as super-Chandrasekhar (Ia-SC) explosions. The ATLAS light curve shows evidence of a short-lived, pulse-like early excess, similar to that detected in another luminous type Ia supernova (SN 2020hvf). The light curve is broad and the early spectra are remarkably similar to SN 2009dc. Adopting a redshift of z=0.026±0.005 for SN 2022ilv based on spectral matching, our model light curve requires a large 56Ni mass in the range 0.7−1.5 M⊙, and a large ejecta mass in the range 1.6−2.3 M⊙. The early excess can be explained by fast-moving SN ejecta interacting with a thin, dense shell of circumstellar material close to the progenitor (∼1013 cm), a few hours after the explosion. This may be realised in a double-degenerate scenario, wherein a white dwarf merger is preceded by ejection of a small amount (∼10−3−10−2 M⊙) of hydrogen and helium-poor tidally stripped material. A deep pre-explosion Pan-STARRS1 stack indicates no host galaxy to a limiting magnitude of r∼24.5. This implies a surprisingly faint limit for any host of Mr≳−11, providing further evidence that these types of explosion occur predominantly in low-metallicity environments.
@article{arxiv.2211.10544,
title = {The luminous type Ia supernova 2022ilv and its early excess emission},
author = {Shubham Srivastav and S. J. Smartt and M. E. Huber and G. Dimitriadis and K. C. Chambers and Michael D. Fulton and Thomas Moore and F. P. Callan and James H. Gillanders and K. Maguire and M. Nicholl and Luke J. Shingles and S. A. Sim and K. W. Smith and J. P. Anderson and Thomas de Boer and Ting-Wan Chen and Hua Gao and D. R. Young},
journal= {arXiv preprint arXiv:2211.10544},
year = {2023}
}