Searching for light echoes due to CSM in SN Ia spectra

TL;DR

This paper develops an analytical model to identify light echoes from circumstellar material in Type Ia supernova spectra, analyzing observational data to distinguish between light echoes and dust sublimation effects.

Contribution

The study introduces a spectral signature-based model for detecting light echoes from CSM in SNe Ia and compares it with observational data to interpret extinction effects.

Findings

Spectral signatures at 4100 Å and 6200 Å can indicate light echoes.

Decreasing extinction due to dust sublimation may explain spectral observations.

A combined model of light echoes and interstellar extinction fits the data better.

Abstract

We present an analytical model for light echoes (LEs) coming from circumstellar material (CSM) around Type Ia Supernovae (SNe Ia). Using this model we find two spectral signatures at 4100 {\AA} and 6200 {\AA} that are useful to identify LEs during the Lira law phase (between 35 and 80 days after maximum light) coming from nearby CSM at distances of 0.01-0.25 pc. We analyze a sample of 89 SNe Ia divided in two groups according to their B-V decline rate during the Lira law phase, and search for LEs from CSM interaction in the group of SNe with steeper slopes by comparing their spectra with our LE model. We find that a model with LEs + pure extinction from interstellar material (ISM) fits better the observed spectra than a pure ISM extinction model that is constant in time, but we find that a decreasing extinction alone explains better the observations without the need of LEs, possibly implying dust sublimation due to the radiation from the SN.