SN 2019muj-a well-observed Type Iax supernova that bridges the luminosity gap of the class

Barna, Barnabas and Szalai, Tamas and Jha, Saurabh W. and Camacho-Neves, Yssavo and Kwok, Lindsey and Foley, Ryan J. and Kilpatrick, Charles D. and Coulter, David A. and Dimitriadis, Georgios and Rest, Armin and Rojas-Bravo, Cesar and Siebert, Matthew R. and Brown, Peter J. and Burke, Jamison and Gonzalez, Estefania Padilla and Hiramatsu, Daichi and Howell, D. Andrew and McCully, Curtis and Pellegrino, Craig and Dobson, Matthew and Smartt, Stephen J. and Swift, Jonathan J. and Stacey, Holland and Rahman, Mohammed and Sand, David J. and Andrews, Jennifer and Wyatt, Samuel and Hsiao, Eric Y. and Anderson, Joseph P. and Chen, Ting-Wan and Della Valle, Massimo and Galbany, Lluis and Gromadzki, Mariusz and Inserra, Cosimo and Lyman, Joe and Magee, Mark and Maguire, Kate and Mueller-Bravo, Tomas E. and Nicholl, Matt and Srivastav, Shubham and Williams, Steven C. (2020) SN 2019muj-a well-observed Type Iax supernova that bridges the luminosity gap of the class. Monthly Notices of the Royal Astronomical Society, 501 (1). pp. 1078-1099. ISSN 0035-8711

Abstract

We present early-time (t < +50 d) observations of SN 2019muj (=ASASSN-19tr), one of the best-observed members of the peculiar SN Iax class. Ultraviolet and optical photometric and optical and near-infrared spectroscopic follow-up started from ∼5 d before maximum light [tmax(B) on $58707.8$ MJD] and covers the photospheric phase. The early observations allow us to estimate the physical properties of the ejecta and characterize the possible divergence from a uniform chemical abundance structure. The estimated bolometric light-curve peaks at 1.05 × 1042 erg s-1 and indicates that only 0.031 M of 56Ni was produced, making SN 2019muj a moderate luminosity object in the Iax class with peak absolute magnitude of $M_\rm {V} = -16.4$ mag. The estimated date of explosion is t0 = $58698.2$ MJD and implies a short rise time of trise = 9.6 d in B band. We fit of the spectroscopic data by synthetic spectra, calculated via the radiative transfer code tardis. Adopting the partially stratified abundance template based on brighter SNe Iax provides a good match with SN 2019muj. However, without earlier spectra, the need for stratification cannot be stated in most of the elements, except carbon, which is allowed to appear in the outer layers only. SN 2019muj provides a unique opportunity to link extremely low-luminosity SNe Iax to well-studied, brighter SNe Iax.