PS1-10afx at z = 1.388: Pan-STARRS1 Discovery of a New Type of Superluminous Supernova
Price, P. A.; Berger, E.; Challis, P.; Kirshner, R. P.; Rest, A.; Foley, R. J.; Smartt, S. J.; Chambers, K. C.; Stubbs, C. W.; Huber, M. E.; Magnier, E. A.; Chornock, R.; Lunnan, R.; Burgasser, A. J.; Tonry, J. L.; Smith, K.; Scolnic, D.; Fong, W.; Burgett, W. S.; Kaiser, N.; Valenti, S.; Riess, A. G.; Soderberg, A. M.; Hodapp, K. W.; Sanders, N. E.; Milisavljevic, D.; Chomiuk, L.; Marion, G. H.; Czekala, I.; Drout, M.; Narayan, G.; Kudritzki, R. -P.; Leibler, C.; Roth, K. C.; McLeod, B.
United States, United Kingdom
Abstract
We present the Pan-STARRS1 discovery of PS1-10afx, a unique hydrogen-deficient superluminous supernova (SLSN) at redshift z = 1.388. The light curve peaked at z P1 = 21.7 mag, making PS1-10afx comparable to the most luminous known SNe, with Mu = -22.3 mag. Our extensive optical and near-infrared observations indicate that the bolometric light curve of PS1-10afx rose on the unusually fast timescale of ~12 days to the extraordinary peak luminosity of 4.1 × 1044 erg s-1 (M bol = -22.8 mag) and subsequently faded rapidly. Equally important, the spectral energy distribution is unusually red for an SLSN, with a color temperature of ~6800 K near maximum light, in contrast to previous hydrogen-poor SLSNe, which are bright in the ultraviolet (UV). The spectra more closely resemble those of a normal SN Ic than any known SLSN, with a photospheric velocity of ~11, 000 km s-1 and evidence for line blanketing in the rest-frame UV. Despite the fast rise, these parameters imply a very large emitting radius (gsim 5 × 1015 cm). We demonstrate that no existing theoretical model can satisfactorily explain this combination of properties: (1) a nickel-powered light curve cannot match the combination of high peak luminosity with the fast timescale; (2) models powered by the spindown energy of a rapidly rotating magnetar predict significantly hotter and faster ejecta; and (3) models invoking shock breakout through a dense circumstellar medium cannot explain the observed spectra or color evolution. The host galaxy is well detected in pre-explosion imaging with a luminosity near L*, a star formation rate of ~15 M ⊙ yr-1, and is fairly massive (~2 × 1010 M ⊙), with a stellar population age of ~108 yr, also in contrast to the young dwarf hosts of known hydrogen-poor SLSNe. PS1-10afx is distinct from known examples of SLSNe in its spectra, colors, light-curve shape, and host galaxy properties, suggesting that it resulted from a different channel than other hydrogen-poor SLSNe.