A Common Origin of Normal Type Ia Supernovae Suggested by the Photometric Diversity

TL;DR

This study analyzes early-phase normal Type Ia supernovae, revealing diversity in their photometric behaviors and suggesting a unified explosion mechanism involving the thin-helium double-detonation scenario.

Contribution

It systematically investigates early photometric features of 67 SNe Ia and proposes a common origin based on the double-detonation model considering viewing angles.

Findings

EExSNe Ia have longer rise times and brighter peaks.

EExSNe Ia show 'red-bump' features in early color evolution.

Photometric diversity can be explained by the double-detonation scenario.

Abstract

In recent years, with an increasing number of type Ia supernovae (SNe Ia) discovered soon after their explosions, a non-negligible fraction of SNe Ia with early-excess emissions (EExSNe Ia) have been confirmed. In this letter, we present a total of \textbf{67} early-phase normal SNe Ia from published papers and ongoing transient survey projects to systematically investigate their photometric behaviors from very early time. We found that EExSNe Ia in our sample have longer rise and brighter peak luminosities compared to those of non-EExSNe Ia. Moreover, EExSNe Ia commonly have ``red-bump" features in the early $B-V$ color while non-EExSNe Ia show blueward evolution from the very beginning. Here, we propose that the thin-helium double-detonation scenario can phenomenologically explain the photometric diversities of normal SNe Ia considering different white dwarf-He-shell mass combinations and the viewing-angle effect, implying a unified explosion mechanism of normal-type SNe Ia. To further testify the possible common origin of normal SNe Ia, systematical studies of multiband photometric and spectral properties of early-phase SNe Ia through the new generation wide-field time-domain survey facilities and global real-time follow-up networks are highly demanded.