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 \sim 40 days in the R band .
Through an analysis of the light curve and the spectral sequence , we estimate a kinetic energy of \sim 7–17 foe and a total ejected mass of \sim 7–17 M _ { \odot } , 5–10 M _ { \odot } of which is oxygen and 0.6–0.7 M _ { \odot } is ^ { 56 } Ni .
The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 M _ { \odot } .
The profile of the forbidden oxygen lines in the nebular spectra show no evidence of a bi-polar geometry in the ejected material .