Discovery of the extremely energetic supernova 2008fz

Abstract

We report on the discovery and initial observations of the energetic type IIn supernova 2008fz. This object was discovered at redshift z = 0.133 and reached an apparent magnitude of V ∼ 17. After correcting for Galactic extinction and redshift, we determine the peak absolute magnitude of the event to be MV = 22.3, placing it among the most luminous supernovae discovered. The optical energy emitted by SN 2008fz (based on the light curve over an 88 day period) is possibly the most ever observed for a supernova (>1.4 ×1051 erg). The event was more luminous than the type IIn SN 2006gy, but exhibited the same smooth, slowly evolving light curve. As is characteristic of type IIn supernova, the early spectra of SN 2008fz initially exhibited narrow Balmer lines which were replaced by a broader component at later times. The spectra also show a blue continuum with no signs of Ca or Na absorption, suggesting that there is little extinction due to dust in the host or circumstellar material. No host galaxy is identified in prior co-added images reaching R ∼ 22. From the supernova's redshift, we place an upper limit on the brightness of the host of MR ∼ ?17 (similar to the brightness of the Small Magellanic Cloud). The presence of the supernova within such a faint galaxy follows the majority of recently discovered highly luminous supernovae. A possible reason for this is the combination of a high star formation rate in low-mass galaxies with a low-metallicity environment. © 2010 The American Astronomical Society.