Properties of Type Iax Supernova 2019muj in the Late Phase: Existence, Nature, and Origin of the Iron-rich Dense Core

Abstract

Type Iax supernovae (SNe Iax) form a class of peculiar SNe Ia, whose early phase spectra share main spectral line identifications with canonical SNe Ia but with higher ionization and much lower line velocities. Their late-time behaviors deviate from usual SNe Ia in many respects; SNe Iax continue showing photospheric spectra over several 100 days and the luminosity decline is very slow. In this work, we study the late-time spectra of SN Iax 2019muj, including a newly presented spectrum at ∼500 days. The spectrum is still dominated by allowed transitions but with a lower ionization state, with possible detection of [O i]λλ6300, 6363. By comprehensively examining the spectral formation processes of allowed transitions (Fe ii, Fe i, and the Ca ii near-IR triplet) and forbidden transitions ([Ca ii]λλ7292, 7324 and [O i]), we quantitatively constrain the nature of the innermost region and find that it is distinct from the outer ejecta; the mass of the innermost component is ∼0.03 M ⊙ dominated by Fe (which can initially be 56Ni), expanding with a velocity of ∼760 km s−1. We argue that the nature of the inner component is explained by the failed/weak white-dwarf thermonuclear explosion scenario. We suggest that a fraction of the 56Ni-rich materials initially confined in (the envelope of) the bound remnant can later be ejected by the energy input through the 56Ni/Co/Fe decay, forming the second unbound ejecta component which manifests itself as the inner dense component seen in the late phase.

Over 500 Days in the Life of the Photosphere of the Type Iax Supernova SN 2014dt

“…Thus, while we cannot rule out an inner core in SN 2014dt, we do not require one. Despite these different inner density profiles, we find remarkable agreement in the photospheric velocities of SN 2014dt and those measured for SN 2019muj by Maeda & Kawabata (2022), even at the latest epochs at ∼+500 days.…”

“…Based on the results of this analysis, along with the remarkable agreement of the n1def model to the spectra of SN 2014dt when using shorter distances, we suggest that the correct distance to M61 is likely less than about 18 Mpc. Maeda & Kawabata (2022) recently analyze the Type Iax SN 2019muj with spectral modeling similar to that presented here. They find evidence for a dense inner core of a few hundredths of a solar mass, in contrast with the density profiles of the deflagration models we use.…”

Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

“…The Subaru/FOCAS spectrum was reduced following standard procedures with IRAF, including bias subtraction, flat-fielding, cosmic-ray rejection, sky subtraction, one-dimensional spectral extraction, wavelength calibration using a ThAr lamp and night-sky lines, and flux calibration with the standard star Feige 34 (e.g., Maeda & Kawabata 2022).…”

SN 2020udy: an SN Iax with strict limits on interaction consistent with a helium-star companion

“…Branch et al 2004 ;Jordan George et al 2012 ;Kromer et al 2013 ;Fink et al 2014 ). Their lower luminosities and expansion velocities compared to normal SNe Ia, as well as the characteristics (multiple components of both permitted and forbidden lines) of their late-time spectra can be explained by this scenario (Jha et al 2006 ;F ole y et al 2016 ;Maeda & Kawabata 2022 ). The likely mixing seen in SN Iax ejecta (measured through o v erlapping v elocities of different species) is also consistent with this scenario (e.g.…”