Supernovae (SNe), the luminous explosions of stars, were observed since
antiquity, with typical peak luminosity not exceeding 1.2x10^{43} erg/s
(absolute magnitude >-19.5 mag). It is only in the last dozen years that
numerous examples of SNe that are substantially super-luminous (>7x10^{43}
erg/s; <-21 mag absolute) were well-documented. Reviewing the accumulated
evidence, we define three broad classes of super-luminous SN events (SLSNe).
Hydrogen-rich events (SLSN-II) radiate photons diffusing out from thick
hydrogen layers where they have been deposited by strong shocks, and often show
signs of interaction with circumstellar material. SLSN-R, a rare class of
hydrogen-poor events, are powered by very large amounts of radioactive 56Ni and
arguably result from explosions of very massive stars due to the pair
instability. A third, distinct group of hydrogen-poor events emits photons from
rapidly-expanding hydrogen-poor material distributed over large radii, and are
not powered by radioactivity (SLSN-I). These may be the hydrogen-poor analogs
of SLSN-II.Comment: This manuscript has been accepted for publication in Science (to
appear August 24). This version has not undergone final editing. Please refer
to the complete version of record at http://www.sciencemag.org/. The
manuscript may not be reproduced or used in any manner that does not fall
within the fair use provisions of the Copyright Act without the prior,
written permission of AAA
