Over a decade ago , a group of supernova explosions with peak luminosities far exceeding ( often by > 100 ) those of normal events , has been identified .
These superluminous supernovae ( SLSNe ) have been a focus of intensive study .
I review the accumulated observations and discuss the implications for the physics of these extreme explosions . \bullet SLSNe can be classified into hydrogen poor ( SLSNe-I ) and hydrogen rich ( SLSNe-II ) events . \bullet Combining photometric and spectroscopic analysis of samples of nearby SLSNe-I and lower-luminosity events , a threshold of M _ { g } < -19.8 mag at peak appears to separate SLSNe-I from the normal population . \bullet SLSN-I light curves can be quite complex , presenting both early bumps and late post-peak undulations . \bullet SLSNe-I spectroscopically evolve from an early hot photospheric phase with a blue continuum and weak absorption lines , through a cool phtospheric phase resembling spectra of SNe Ic , and into the late nebular phase . \bullet SLSNe-II are not nearly as well studied , lacking information based on large sample studies .
Proposed models for the SLSN power source are challenged to explain all the observations .
SLSNe arise from massive progenitors , with some events associated with very massive stars ( M > 40 M _ { \odot } ) .
Host galaxies of SLSNe in the nearby universe tend to have low mass and sub-solar metallicity .
SLSNe are rare , with rates < 100 times lower than ordinary SNe .
SLSN cosmology and their use as beacons to study the high-redshift universe offer exciting future prospects .