On the triple peaks of SNHunt248 in NGC 5806

TL;DR

This study analyzes the complex light curve and spectral energy distribution of SNHunt248, a supernova impostor, revealing multiple circumstellar interactions and a luminous yellow hypergiant progenitor with historical variability.

Contribution

It provides a detailed multi-year observational analysis of SNHunt248, highlighting its triple-peaked light curve and the nature of its progenitor star, which was brighter than typical Galactic hypergiants.

Findings

The light curve shows three distinct peaks with the brightest at -15.0 mag.

Spectral energy distribution matches a 6700 K blackbody with log luminosity 6.1.

The progenitor was a luminous yellow hypergiant brighter than known Galactic counterparts.

Abstract

We present our findings on a supernova (SN) impostor, SNHunt248, based on optical and near-IR data spanning $\sim$15 yrs before discovery, to $\sim$1 yr post-discovery. The light curve displays three distinct peaks, the brightest of which is at $M_{R} \sim -15.0$ mag. The post-discovery evolution is consistent with the ejecta from the outburst interacting with two distinct regions of circumstellar material. The 0.5 - 2.2 $\mu$m spectral energy distribution at -740 d is well-matched by a single 6700 K blackbody with $\log(L/L_\odot) \sim 6.1$. This temperature and luminosity support previous suggestions of a yellow hypergiant progenitor; however, we find it to be brighter than the brightest and most massive Galactic late-F to early-G spectral type hypergiants. Overall the historical light curve displays variability of up to $\sim \pm1$ mag. At current epochs ($\sim$1 yr post-outburst), the absolute magnitude ($M_{R} \sim -9$ mag) is just below the faintest observed historical absolute magnitude $\sim$10 yrs before discovery.