SN 2006gy: An extremely luminous supernova in the early-type galaxy NGC 1260

E. O. Ofek, P. B. Cameron, M. M. Kasliwal, A. Gal-Yam, A. Rau, S. R. Kulkarni, D. A. Frail, P. Chandra, S. B. Cenko, A. M. Soderberg, S. Immler

Abstract: With an extinction-corrected V-band peak absolute magnitude of about -22.2, supernova (SN) 2006gy is probably the brightest SN ever observed. We report on multi-wavelength observations of this SN and its environment. The optical spectra and the slow light-curve evolution resemble those of members of the hybrid IIn/Ia SN class, also called type-IIa SNe. The total radiated energy in the first two months is about 1.2 x 10^51 erg, comparable to the total mechanical energy release of a type-Ia SN. If the engine behind SN2006gy is a type-Ia SN, the rapid conversion of mechanical energy to radiation requires a very dense circumstellar medium, which in turns implies an extreme mass loss rate for the progenitor, ~10^-2 solar mass per year over a period of ~100 yr prior to explosion. Such a mass-loss rate is a challenging requirement for most proposed models of type-IIa SN. Unlike the four previously known type-IIa SNe, the host galaxy NGC 1260 is not a star-forming galaxy, but rather an S0 galaxy dominated by an old stellar population, which probably has a relatively high metallicity. However, our high resolution adaptive optics images reveal a dust lane in this galaxy, passing about 300 pc (projected) from the SN position. These observations add more questions as to the origin of the enigmatic IIa supernovae.