On the triple peaks of SNHunt248 in NGC 5806^⋆

¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, BT7 1NN, UK
e-mail: e.kankare@qub.ac.uk
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁵ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
⁸ Department of Astronomy, The Oskar Klein Center, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁹ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
¹⁰ Millennium Institute of Astrophysics, Casilla 36-D, Santiago, Chile
¹¹ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Received: 29 May 2015
Accepted: 17 August 2015

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 M_R ~ −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 (M_R ~ − 9 mag) is just below the faintest observed historical absolute magnitude ~10 yr before discovery.