The Evolution of Late-Time Optical Emission From SN 1979C

TL;DR

This study tracks the optical emission evolution of SN 1979C over 11 to 29 years, revealing flux decreases, profile narrowing, and potential Wolf-Rayet star signatures, enhancing understanding of late-time supernova behavior.

Contribution

It provides the first detailed comparison of late-time optical spectra of SN 1979C over nearly three decades, highlighting common features in similar supernovae and identifying possible Wolf-Rayet star signatures.

Findings

Halpha flux decreased by ~35% from 1993 to 2008

Narrowing of oxygen emission line profiles observed

Possible Wolf-Rayet star signatures detected

Abstract

Optical spectra of the bright Type II-L supernova SN 1979C obtained in April 2008 with the 6.5 m MMT telescope are compared with archival late-time spectra to follow the evolution of its optical emission over the age range of 11 to 29 years. We estimate an Halpha flux decrease of around 35% from 1993 to 2008 but noticeable increases in the strength of blueshifted emission of forbidden oxygen lines. While the maximum expansion of the broad ~6700 km/s Halpha emission appears largely unchanged from 1993, we find a significant narrowing of the double-peaked emission profiles in the [O I] 6300, 6364 and [O II] 7319, 7330 lines. A comparison of late-time optical spectra of a few other Type II supernovae which, like SN 1979C, exhibit bright late-time X-ray, optical, and radio emissions, suggests that blueshifted double-peaked oxygen emission profiles may be a common phenomenon. Finally, detection of a faint, broad emission bump centered around 5800 Angstroms suggests the presence of WC type Wolf-Rayet stars in the supernova's host star cluster.