No plateau observed in late-time near-infrared observations of the underluminous Type Ia supernova 2021qvv
Galbany, L.; Rest, A.; Howell, D. A.; Handberg, R.; Maguire, K.; Stritzinger, M. D.; Karamehmetoglu, E.; Graur, O.; McCully, C.; Burke, J.; Hiramatsu, D.; Pellegrino, C.; Riess, A. G.; Jha, S. W.; Hosseinzadeh, G.; Seitenzahl, I. R.; Terreran, G.; Zurek, D. R.; Padilla Gonzalez, E.; Deckers, M.; Fisher, R.; Fullard, A. G.; Kerzendorf, W. E.; Newsome, M.; Shara, M. M.; Shen, K. J.
United Kingdom, United States, Ireland, Spain, Denmark, Australia
Abstract
Near-infrared (NIR) observations of normal Type Ia supernovae (SNe Ia) obtained between 150 and 500 d past maximum light reveal the existence of an extended plateau. Here, we present observations of the underluminous, 1991bg-like SN 2021qvv. Early, ground-based optical and NIR observations show that SN 2021qvv is similar to SN 2006mr, making it one of the dimmest, fastest evolving 1991bg-like SNe to date. Late-time (170-250 d) Hubble Space Telescope observations of SN 2021qvv reveal no sign of a plateau. An extrapolation of these observations backwards to earlier-phase NIR observations of SN 2006mr suggests the complete absence of an NIR plateau, at least out to 250 d. This absence may be due to a higher ionization state of the ejecta, as predicted by certain sub-Chandrasekhar-mass detonation models, or to the lower temperatures of the ejecta of 1991bg-like SNe, relative to normal SNe Ia, which might preclude their becoming fluorescent and shifting ultraviolet light into the NIR. This suggestion can be tested by acquiring NIR imaging of a sample of 1991bg-like SNe that covers the entire range from slowly evolving to fast-evolving events (0.2 ≲ sBV ≲ 0.6). A detection of the NIR plateau in slower evolving, hotter 1991bg-like SNe would provide further evidence that these SNe exist along a continuum with normal SNe Ia. Theoretical progenitor and explosion scenarios would then have to match the observed properties of both SN Ia subtypes.