A Luminous and Fast-Expanding Type Ib Supernova SN 2012au
  We present a set of photometric and spectroscopic observations of a bright
Type Ib supernova SN 2012au from -6d until ~+150d after maximum. The shape of
its early R-band light curve is similar to that of an average Type Ib/c
supernova. The peak absolute magnitude is M_R=-18.7+-0.2 mag, which suggests
that this supernova belongs to a very luminous group among Type Ib supernovae.
The line velocity of He I {\lambda}5876 is about 15,000 km/s around maximum,
which is much faster than that in a typical Type Ib supernova. From the
quasi-bolometric peak luminosity of (6.7+-1.3)x10^(42) erg/s, we estimate the
\Ni mass produced during the explosion as ~0.30 Msun. We also give a rough
constraint to the ejecta mass 5-7 Msun and the kinetic energy (7-18)x10^(51)
erg. We find a weak correlation between the peak absolute magnitude and He I
velocity among Type Ib SNe. The similarities to SN 1998bw in the density
structure inferred from the light curve model as well as the large peak
bolometric luminosity suggest that SN 2012au had properties similar to
energetic Type Ic supernovae.
