Abstract
We present the discovery of two ultra-luminous supernovae (SNe) at z ~ 0.9 with the Pan-STARRS1 Medium-Deep Survey. These SNe, PS1-10ky and PS1-10awh, are amongst the most luminous SNe ever discovered, comparable to the unusual transients SN 2005ap and SCP 06F6. Like SN 2005ap and SCP 06F6, they show characteristic high luminosities (M_bol ~ -22.5 mag), blue spectra with a few broad absorption lines, and no evidence for H or He. We have constructed a full multi-color light curve sensitive to the peak of the spectral energy distribution in the rest-frame ultraviolet, and we have obtained time-series spectroscopy for these SNe. Given the similarities between the SNe, we combine their light curves to estimate a total radiated energy over the course of explosion of (0.9-1.4) x 10^51 erg. We find photospheric velocities of 12,000-19,000 km/s with no evidence for deceleration measured across ~3 rest-frame weeks around light-curve peak, consistent with the expansion of an optically-thick massive shell of material. We show that, consistent with findings for other ultra-luminous SNe in this class, radioactive decay is not sufficient to power PS1-10ky, and we discuss two plausible origins for these events: the initial spin-down of a newborn magnetar in a core-collapse SN, or SN shock breakout from the dense circumstellar wind surrounding a Wolf-Rayet star.
Highlights
The observational and physical parameter space occupied by supernovae (SNe) has expanded dramatically because of the recent discovery of several ultraluminous SNe
We note that the measured evolution of the radius (Figure 8) is consistent with a shell that begins expanding at constant velocity from a very small radius around Day −40 or Day −30, roughly coincident with the first detections of SN 2005ap-like sources; our radius calculations are very uncertain, and better temperature determinations before light curve maximum are required to constrain the radius at early times
Using multi-color photometry and multi-epoch spectroscopy, we find that PS1-10ky and PS1-10awh radiate ∼1051 erg in just a few months, making them among the most energetic SNe known
Summary
The observational and physical parameter space occupied by supernovae (SNe) has expanded dramatically because of the recent discovery of several ultraluminous SNe. SN 2005ap and SCP 06F6 were tied together into a common class of transients by Quimby et al (2011, Q+11), who collected four additional SN 2005aplike sources discovered by the Palomar Transient Factory (PTF) They identified narrow Mg ii λλ2796,2803 absorption lines in their spectra, presumably associated with the interstellar media of the host galaxies. A common set of observational properties began to emerge for the SN 2005ap-like objects In addition to their very high peak luminosities, these sources typically show distinctive symmetric light curves with rise times of ∼20–50 of days in the rest frame.
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