Explosion of a massive, He-rich star at z = 0.16

Abstract

We present spectroscopic and photometric data of the peculiar type Ib supernova 2001 gh, discovered by the Southern inTermediate Redshift ESO Supernova Search at a redshift z = 0.16. SN 2001 gh has high luminosity at maximum, while the light curve shows a broad, delayed peak. An early-time spectrum shows an almost featureless blue continuum with a few weak P-Cygni lines that we attribute to He I. He I lines remain the only spectral features visible in another spectrum obtained one month later. Three possible scenarios are considered: a massive and energetic progenitor with M_(ejecta)~30M_⊙, E~6x10^(52) erg and earlier explosion date; a moderate-mass progenitor with M_(ejecta)~15M_⊙, M_(Ni) = 0.65M_⊙ and E~18x10^(51) erg; or a more canonical SN Ib with a dense, circumstellar shell

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