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

Abstract

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 to B-band maximum, LSQ14fmg is already brighter than mag before host extinction correction. The observed color curves show a flat evolution from the earliest observation to approximately 1 week after maximum. The near-infrared light curves peak brighter than −20.5 mag in the J and H bands, 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 56Ni. 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 past B-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.

An imaging polarimetry survey of Type Ia supernovae: are peculiar extinction and polarization properties produced by circumstellar or interstellar matter?

“…The curves in PPNe are shown to be produced by CSM scattering (Oppenheimer et al 2005). Therefore, the common continuum polarization properties between PPNe and SNe Ia might be an indication that some SNe Ia explode within a PPN after the WD (formed from the initially more-massive star) merges with the core of the companion AGB star during the common-envelope phase (core-degenerate scenario, Kashi & Soker 2011; see also Jones & Boffin 2017;Soker 2019a,b;Chiotellis et al 2021;Hsiao et al 2020;Wu et al 2021;Ashall et al 2021).…”

Parameterized nonrelativistic limit of stellar structure equations in Ricci-based gravity theories

“…Regarding the description of stellar structure, RBGs are capable to modify the mass-radius relations of neutron stars, which allows to raise their maximum mass with realistic equation of state to match observations of neutron stars above two solar masses [51]; and also alter the Chandrasekhar's limit of white dwarfs, which might allow to address the existence of super-Chandrasekhar white dwarfs, whose masses are suggested to be up to two times the standard Chandrasekhar limit [52][53][54][55] (see chapter 3 of [28] for details on these issues). Moreover, the nonrelativistic limits of some RBGs have been recently employed to work out the minimum main sequence mass of quadratic fðRÞ gravity [56] and or the minimum deuterium burning mass for Eddington-inspired Born-Infeld gravity (EiBI, [39]), where the current modeling of these scenarios and their compatibility with observations still leaves some room for modifications of GR, becoming a source of strong constraints on the parameters of RBGs.…”

ASASSN-15hy: an under-luminous, red 03fg-like type Ia supernova

“…One of the most rare peculiar sub-types is the "super-Chandrasekhar" or 03fg-like SNe. 1 To date there have only been a handful of well-studied SNe Ia identified as members of this sub-type, including: SN 2003fg (Howell et al 2006), SN 2006gz (Hicken et al 2007Maeda et al 2009), SN 2007if (Scalzo et al 2010Yuan et al 2010;Childress et al 2011), SN 2009dc (Yamanaka et al 2009Tanaka et al 2010;Silverman et al 2011;Taubenberger et al 2011;Hachinger et al 2012), SN 2012dn (Chakradhari et al 2014Parrent et al 2016;Nagao et al 2017;Taubenberger et al 2019), ASASSN-15pz (Chen et al 2019), and LSQ14fmg (Hsiao et al 2020).…”

“…Early suggestions of single degenerate, rapid rotating super-M Ch WD (Howell et al 2006;Hachisu et al 2012) have been challenged since the model simulations could not reproduce the slow expansion velocities on top of the high luminosity regardless of the explosion mechanism, such as pure detonation, pure deflagration and delayed detonation (e.g., Pfannes et al 2010;Hachinger et al 2012;Fink et al 2018). The "interaction" (e.g., Yuan et al 2010;Hachinger et al 2012;Taubenberger et al 2013;Noebauer et al 2016;Taubenberger et al 2019) or "envelope" models (e.g., Khokhlov et al 1993;Hoeflich & Khokhlov 1996;Scalzo et al 2010Scalzo et al , 2014Hsiao et al 2020), in which the interaction between the exploding WD and surrounding circumstellar medium (CSM) provides an additional energy source and slows down the expansion, present a promising route to explain these peculiar events. Recent works have shown photometric evidence of CSM such as the NIR excess in SN 2012dn (Yamanaka et al 2016;Nagao et al 2017) and possible wind interaction in LSQ14fmg (Hsiao et al 2020).…”

“…The "interaction" (e.g., Yuan et al 2010;Hachinger et al 2012;Taubenberger et al 2013;Noebauer et al 2016;Taubenberger et al 2019) or "envelope" models (e.g., Khokhlov et al 1993;Hoeflich & Khokhlov 1996;Scalzo et al 2010Scalzo et al , 2014Hsiao et al 2020), in which the interaction between the exploding WD and surrounding circumstellar medium (CSM) provides an additional energy source and slows down the expansion, present a promising route to explain these peculiar events. Recent works have shown photometric evidence of CSM such as the NIR excess in SN 2012dn (Yamanaka et al 2016;Nagao et al 2017) and possible wind interaction in LSQ14fmg (Hsiao et al 2020). However, the nature of the "envelope" is still under debate (e.g., pre-explosion wind material, the product of double degenerate merger, or the envelope of an AGB star in the core degenerate scenario; Kashi & Soker 2011;Ilkov & Soker 2012;Aznar-Siguán et al 2015) and there is currently no spectral evidence of interaction observed so far.…”