No plateau observed in late-time near-infrared observations of the underluminous Type Ia supernova 2021qvv

• Published in: Monthly notices of the Royal Astronomical Society 2023-09, Vol.526 (2), p.2977-2990
• Main Authors: Graur, O, Padilla Gonzalez, E, Burke, J, Deckers, M, Jha, S W, Galbany, L, Karamehmetoglu, E, Stritzinger, M D, Maguire, K, Howell, D A, Fisher, R, Fullard, A G, Handberg, R, Hiramatsu, D, Hosseinzadeh, G, Kerzendorf, W E, McCully, C, Newsome, M, Pellegrino, C, Rest, A, Riess, A G, Seitenzahl, I R, Shara, M M, Shen, K J, Terreran, G, Zurek, D R
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad2960

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.