Carnegie Supernova Project II: The Slowest Rising Type Ia Supernova LSQ14fmg and Clues to the Origin of Super-Chandrasekhar/03fg-like Events

Hsiao, E. Y.; Hoeflich, P.; Ashall, C.; Lu, J.; Contreras, C.; Burns, C. R.; Phillips, M. M.; Galbany, L.; Anderson, J. P.; Baltay, C.; Baron, E.; Castellon, S.; Davis, S.; Freedman, Wendy L.; Gall, C.; Gonzalez, C.; Graham, M. L.; Hamuy, M.; Holoien, T. W. -S.; Karamehmetoglu, E.; Krisciunas, K.; Kumar, S.; Kuncarayakti, H.; Morrell, N.; Moriya, T. J.; Nugent, P. E.; Perlmutter, S.; Persson, S. E.; Piro, A. L.; Rabinowitz, D.; Roth, M.; Shahbandeh, M.; Shappee, B. J.; Stritzinger, M. D.; Suntzeff, N. B.; Taddia, F.; Uddin, S. A.
2020
ASTROPHYSICAL JOURNAL
DOI
10.3847/1538-4357/abaf4c
The Type Ia supernova (SN Ia) LSQ14fmg exhibits exaggerated properties that may help to reveal the origin of the "super-Chandrasekhar" (or 03fg-like) group. The optical spectrum is typical of a 03fg-like SN Ia, but the light curves are unlike those of any SNe Ia observed. The light curves of LSQ14fmg rise extremely slowly. At -23 rest-frame days relative toB-band maximum, LSQ14fmg is already brighter thanJandHbands, far more luminous than any 03fg-like SNe Ia with near-infrared observations. At 1 month past maximum, the optical light curves decline rapidly. The early, slow rise and flat color evolution are interpreted to result from an additional excess flux from a power source other than the radioactive decay of the synthesized Ni-56. The excess flux matches the interaction with a typical superwind of an asymptotic giant branch (AGB) star in density structure, mass-loss rate, and duration. The rapid decline starting at around 1 month pastB-band maximum may be an indication of rapid cooling by active carbon monoxide (CO) formation, which requires a low-temperature and high-density environment. These peculiarities point to an AGB progenitor near the end of its evolution and the core degenerate scenario as the likely explosion mechanism for LSQ14fmg.