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.

SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event

“…Our inferred CSM properties are similar to those of SN 2020hvf and SN 2022ilv, for which Jiang et al (2021) and Srivastav et al (2023) find 𝑀 CSM = 0.01 and 0.001 M , respectively, with 𝑅 env = 1 × 10 13 cm. However, the epoch of SN 2021zny's flux excess was observed in four photometric bands, including the dense TESS-band coverage, as opposed to one band for SNe 2020hvf and 2022ilv, allowing us to better constrain the black body temperature of the CSM-powered luminosity component and the time of explosion.…”

“…4, we show the absolute 𝐵-band peak magnitude against Δ𝑚 15 (𝐵) for a sample of well-observed 03fg-like SNe Ia, alongside the CfA SN Ia sample from Hicken et al (2009). The intrinsic diversity of the 03fg-like SN Ia population is evident in this parameter space, with next to the usual population of high luminosity and slowly evolving SNe 2003fg (Howell et al 2006), 2007if (Scalzo et al 2010), 2009dc (Taubenberger et al 2011), 2020hvf (Jiang et al 2021) and 2022ilv (Srivastav et al 2023) lying the slightly dimmer 2006gz (Hicken et al 2007) and ASASSN-15pz (Chen et al 2019), the slightly dimmer but faster evolving LSQ14fmg (Hsiao et al 2020) and 2020esm (Dimitriadis et al 2022), the faint and faster evolving 2012dn (Taubenberger et al 2019) and the faint and slow evolving ASASSN-15hy (Lu et al 2021). SN 2021zny lies on the extreme end of the magnitude-decline range, with Δ𝑚 15 (𝐵) values similar to the slow evolving SNe 2006gz, 2007if and 2009dc, with its peak luminosity being ∼ 0.33 mag brighter than what is expected for its decline rate.…”

“…Recently, a short-lived flash of optical emission was observed for two overluminous SNe Ia, 2020hvf (Jiang et al 2021) and 2022ilv (Srivastav et al 2023). For SN 2020hvf, the flux excess was observed during the high cadence Tomo-e Gozen transient survey, using the camera's clear filter, and lasted for ∼ 1 day, while for SN 2022ilv, observations in the ATLAS o-band showed a similar early time behaviour.…”

Initial Flash and Spectral Formation of Type Ia Supernovae with An Envelope: Applications to Over-luminous SNe Ia

“…Evolutionary scenarios leading to the formation and explosion of a 𝑀 sup−Ch WD have thus been considered and proposed by various researchers (see Section 4.4 for further details). However, with an increasing number of similar events, a huge diversity has been noticed within this 'over-luminous' class, current classification of which is largely based on the spectral similarity and slow evolution in the light curve; some of them may be just moderately luminous (depending on the treatment of the host extinction which is frequently very uncertain) and/or the velocities seen in the spectral lines are not always slow (e.g., Hicken et al 2007;Scalzo et al 2010;Chakradhari et al 2014;Yamanaka et al 2016;Ashall et al 2021;Srivastav et al 2023).…”

“…While this scenario has not been rejected in general, at least three counter examples have been recently reported; SN 2020hvf, which also falls into the category of the over-luminous class (while its peak luminosity is just moderately high, with a large uncertainty of the host extinction), showed a sub-day time-scale bright flash within a day of the putative explosion date (Jiang et al 2021). Recently added are SNe 2021zny (Dimitriadis et al 2023) and 2022ilv (Srivastav et al 2023), which show a similar initial flash; while the sample is still limited, the initial flash is generally (so far always) found for the over-luminous SNe Ia when prompt photometric observations just after the explosion are conducted with sufficiently high sensitivity. If the SN-CSM interaction scenario would be to provide a major power input to the system, such a short time-scale phenomenon must be diluted out, irrespective of the origin of the flash.…”