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 ∼15 yr before discovery, to ∼1 yr post-discovery. The light curve displays three distinct peaks, the brightest of which is at MR ∼ −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 μm spectral energy distribution at −740 d is well-matched by a single 6700 K blackbody with log(L/L ) ∼ 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 ∼±1 mag. At current epochs (∼1 yr post-outburst), the absolute magnitude (MR ∼ −9 mag) is just below the faintest observed historical absolute magnitude ∼10 yr before discovery