The Luminous Type Ia Supernova 2022ilv and Its Early Excess Emission

Abstract

We present observations and analysis of the hostless 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 Asteroid Terrestrial-impact Last Alert System 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 those of 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 realized in a double-degenerate scenario, wherein a white dwarf merger is preceded by the 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 M r ≳ −11, providing further evidence that these types of explosions occur predominantly in low-metallicity environments.