We present the Pan-STARRS1 discovery and light curves , and follow-up MMT and Gemini spectroscopy of an ultra-luminous supernova ( ULSN ; dubbed PS1-11bam ) at a redshift of z = 1.566 with a peak brightness of M _ { UV } \approx - 22.3 mag .
PS1-11bam is one of the highest redshift spectroscopically-confirmed SNe known to date .
The spectrum is characterized by broad absorption features typical of previous ULSNe ( e.g. , C ii , Si iii ) , and by strong and narrow Mg ii and Fe ii absorption lines from the interstellar medium ( ISM ) of the host galaxy , confirmed by an [ O ii ] \lambda 3727 emission line at the same redshift .
The equivalent widths of the Fe ii \lambda 2600 and Mg ii \lambda 2803 lines are in the top quartile of the quasar intervening absorption system distribution , but are weaker than those of gamma-ray burst intrinsic absorbers ( i.e. , GRB host galaxies ) .
We also detect the host galaxy in pre-explosion Pan-STARRS1 data and find that its UV spectral energy distribution is best fit with a young stellar population age of \tau _ { * } \approx 15 - 45 Myr and a stellar mass of M _ { * } \approx ( 1.1 - 2.6 ) \times 10 ^ { 9 } M _ { \odot } ( for Z = 0.05 - 1 Z _ { \odot } ) .
The star formation rate inferred from the UV continuum and [ O ii ] \lambda 3727 emission line is \approx 10 M _ { \odot } yr ^ { -1 } , higher than in any previous ULSN host .
PS1-11bam provides the first direct demonstration that ULSNe can serve as probes of the interstellar medium in distant galaxies .
At the present , the depth and red sensitivity of PS1 are uniquely suited to finding such events at cosmologically interesting redshifts ( z \sim 1 - 2 ) ; the future combination of LSST and 30-m class telescopes promises to extend this technique to z \sim 4 .