On the triple peaks of SNHunt248 in NGC 5806

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 $\hat{I}¼$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 $\sim \pm 1$ 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.

7 pages, 3 figures, accepted for A&A Letters