A Search for Supernova Light Echoes in NGC 6946 with SITELLE

TL;DR

This study used spectroscopic observations with SITELLE to search for supernova light echoes in NGC 6946, developing a novel detection method based on identifying specific spectral features, but found no evidence of light echoes.

Contribution

The paper introduces a new spectroscopic technique for detecting supernova light echoes using negatively sloped continua as indicators.

Findings

No supernova light echoes detected above the surface brightness limit.

Developed a novel spectroscopic search method for light echoes.

Applied the method to NGC 6946's historical supernovae.

Abstract

We present the analysis of four hours of spectroscopic observations of NGC 6946 with the SITELLE Imaging Fourier Transform Spectrometer on the Canada-France-Hawaii Telescope, acquired to search for supernova light echoes from its ten modern supernovae. We develop a novel spectroscopic search method: identifying negatively sloped continua in the narrow-band SN3 filter as candidate highly-broadened P-Cygni profiles in the H$\alpha$ line, which would be characteristic of the spectra of supernovae ejecta. We test our methodology by looking for light echoes from any of the ten supernovae observed in NGC 6946 in the past 100 years. We find no evidence of light echoes above the survey surface brightness limit of 1$\times$10$^{-15}$erg/s/cm$^2$/arcsec$^2$.