High $\gamma$-ray escape time in 2003fg-like supernovae: A challenge to proposed models

TL;DR

This study investigates the gamma-ray escape times in 2003fg-like supernovae, revealing higher escape times than normal Type Ia supernovae and challenging existing explosion models, with collisions of massive white dwarfs showing better agreement.

Contribution

It provides the first detailed gamma-ray escape time analysis for 2003fg-like SNe and tests various explosion models against observed data, highlighting the limitations of current theories.

Findings

2003fg-like SNe have gamma-ray escape times of 45-60 days.

These supernovae are distinct from normal SNe Ia in the t0-M_Ni56 plane.

White dwarf collision models better match observations than merger or single-star models.

Abstract

A rare subclass of Type Ia supernovae (SNe Ia), named after the prototype SN 2003fg, includes some of the brightest SNe Ia, often called "super Chandrasekhar-mass" SNe Ia. We calculate the $\gamma$-ray deposition histories and the $^{56}$Ni mass synthesized in the explosion, $M_\mathrm{Ni56}$, for eight 2003fg-like SNe. Our findings reveal that the $\gamma$-ray escape time, $t_0$, for these objects is $ t_0\approx45\text{-}60 \,$ days, significantly higher than that of normal SNe Ia. 2003fg-like SNe are distinct from normal SNe Ia in the $ t_0 $-$ M_\mathrm{Ni56} $ plane, with a noticeable gap between the two populations. The observed position of 2003fg-like SNe in this plane poses a significant challenge for theoretical explosion models. We demonstrate that the merger of two white dwarfs (WDs) and a single star exceeding the Chandrasekhar limit fail to reproduce the observed $ t_0 $-$ M_\mathrm{Ni56} $ distribution. However, preliminary calculations of head-on collisions of massive WDs show agreement with the observed $ t_0 $-$ M_\mathrm{Ni56} $ distribution.