2012ApJ...749L..28V

We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was ∼40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of ∼7-17 foe and a total ejected mass of ∼7-17 M_☉, 5-10 M_☉ of which is oxygen and 0.6-0.7 M _☉ is ⁵⁶Ni. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 M_☉. The profile of the forbidden oxygen lines in the nebular spectra shows no evidence of a bi-polar geometry in the ejected material.