SN 2014J in M82: New Insights On the Spectral Diversity of Type Ia Supernovae

TL;DR

This study provides detailed spectroscopic analysis of SN 2014J, revealing its spectral diversity and challenging existing classifications of Type Ia supernovae, with implications for understanding their progenitors and explosion mechanisms.

Contribution

It offers new insights into the spectral diversity of Type Ia supernovae, especially regarding the high-velocity and low velocity gradient subgroup characteristics.

Findings

SN 2014J is classified as high-velocity with low velocity gradient.

HV+LVG SNe Ia show higher photospheric temperatures and more complete burning.

Spectral features suggest differences in progenitor explosion processes.

Abstract

We present extensive spectroscopic observations for one of the closest type Ia supernovae (SNe Ia), SN 2014J discovered in M82, ranging from 10.4 days before to 473.2 days after B-band maximum light. The diffuse interstellar band (DIB) features detected in a high-resolution spectrum allow an estimate of line-of-sight extinction as Av=1.9+/-0.6 mag. Spectroscopically, SN 2014J can be put into the high-velocity (HV) subgroup in Wang's classification with a velocity of Si~II 6355 at maximum light as about 12200 km/s, but has a low velocity gradient (LVG, following Benetti's classification) as 41+/-2 km/s/day, which is inconsistent with the trend that HV SNe Ia generally have larger velocity gradients. We find that the HV SNe Ia with LVGs tend to have relatively stronger Si III (at ~4400 Angstrom) absorptions in early spectra, larger ratios of S II 5468 to S II 5640, and weaker Si II 5972 absorptions compared to their counterparts with similar velocities but high velocity gradients. This shows that the HV+LVG subgroup of SNe Ia may have intrinsically higher photospheric temperature, which indicates that their progenitors may experience more complete burning in the explosions relative to the typical HV SNe Ia.