Observational properties of low-redshift pair instability supernovae

Abstract

So called superluminous supernovae have been recently discovered in the local Universe. It appears possible that some of them originate from stellar explosions induced by the pair instability mechanism. Recent stellar evolution models also predict pair instability supernovae (PISNe) from very massive stars at fairly high metallicities (i.e. Z~0.004). We provide supernova (SN) models and synthetic light curves for two progenitor models, a 150 Msun red-supergiant and a 250 Msun yellow-supergiant at a metallicity of Z=0.001, for which the evolution from the main sequence to collapse, and the initiation of the PISN itself, has been previously computed in a realistic and self-consistent way. We are using the radiation hydrodynamics code STELLA to describe the SN evolution of both models over a time frame of about 500 days. We describe the shock-breakout phases of both SNe which are characterized by a higher luminosity, a longer duration and a lower effective temperature than those of ordinary SNeIIP. We derive the bolometric as well as the U, B, V, R and I light curves of our PISN models, which show a long-lasting plateau phase with maxima at Mbol=-19.3 mag and -21.3 mag for our lower and higher mass model, respectively. We also describe the photospheric composition and velocity as function of time. We conclude that the light curve of the explosion of our initially 150 Msun star resembles those of relatively bright SNeIIP, whereas its photospheric velocity at early times is smaller. Its 56Ni mass of 0.04 Msun also falls well into the range found in ordinary core collapse SNe. The light curve and photospheric velocity of our 250 Msun models has a striking resemblance with that of the superluminous SN2007bi, strengthening its interpretation as PISN. We conclude that PISNe may occur more frequently in the local universe than previously assumed.