Supernova Progenitors, Their Variability, and the Type IIP Supernova ASASSN-16fq in M66

TL;DR

This study identifies the progenitor of a Type IIP supernova in archival HST data, constrains its initial mass, and finds no significant variability in the progenitor over 8 years, providing insights into supernova progenitors.

Contribution

First identification of a supernova progenitor in archival data with mass estimates and variability constraints, enhancing understanding of progenitor characteristics before explosion.

Findings

Progenitor had an initial mass of 8-12 solar masses.

No significant variability detected over 8 years.

Constraints on pre-supernova outbursts are N<3 for outbursts >0.1 years and brighter than M_R<-8 mag.

Abstract

We identify a pre-explosion counterpart to the nearby Type IIP supernova ASASSN-16fq (SN 2016cok) in archival Hubble Space Telescope (HST) data. The source appears to be a blend of several stars that prevents obtaining accurate photometry. However, with reasonable assumptions about the stellar temperature and extinction, the progenitor almost certainly had an initial mass M<17Msun, and was most likely in the mass range 8-12Msun. Observations once ASASSN-16fq has faded will have no difficulty accurately determining the properties of the progenitor. In 8 years of Large Binocular Telescope (LBT) data, no significant progenitor variability is detected to RMS limits of roughly 0.03 mag. Of the six nearby SN with constraints on low level variability, SN 1987A, SN 1993J, SN 2008cn, SN 2011dh, SN 2013ej and ASASSN-16fq, only the slowly fading progenitor of SN 2011dh showed clear evidence of variability. Excluding SN 1987A, the 90% confidence limit implied by these sources on the number of outbursts over the last decade before the SN that last longer than 0.1 years (FWHM) and are brighter than M_R<-8 mag is approximately N<3. Our continuing LBT monitoring program will steadily improve constraints on pre-SN progenitor variability at amplitudes far lower than achievable by SN surveys.