The supernova rate in starburst galaxies

We conducted an optical CCD search for supernovae in a sample of 142 bright [m(B) less than or equal to 16 mag], nearby (z less than or equal to 0.03) starburst galaxies over the period 1988 December to 1991 June, to a limiting R-band magnitude of 18. Five supernovae were found, in all cases outside the host galaxy's nucleus. We determine supernova rates (in supernova units or SNU) in the extranuclear regions to be 0.7 h(2) SNU for Type Ia, 0.7 h(2) SNU for Type Ib/c, and similar to 0.6 h(2) SNU for Type II, with large uncertainties but upper limits of 2.2 h(2), 2.5 h(2), and 1.7 h(2) SNU, respectively. These rates are similar to those measured in "normal" galaxies. We found no evidence for a supernova-induced brightening in any galactic nucleus and, with a few reasonable assumptions, can place upper limits of 9 h(2), 12 h(2), and 7 h(2) SNU on the rates of unobscured supernovae Types Ia, Ib/c, and II, respectively, inside the nuclei.