REDISCUSSION OF EXTRAGALACTIC SUPERNOVA RATES DERIVED FROM EVANS 1980-1988 OBSERVATIONS

Supernova rates are derived from observations by Evans under the assum ption that (1) the discovery probability of supernovae is independent of parent galaxy inclination and (2) supernovae of all types have lumi nosity functions of finite width at maximum light. For spirals of type s Sab-Sd the total supernova rate is calculated to be approximately 1. 3(H0/75)2 SNu. Modeling shows that symmetrical broadening of the lumin osity functions of supernovae at maximum light does not change the sup ernova rates significantly from those computed from Evans's observatio ns under the assumption that each type of supernova has a single value of M(V)(max). However, systematic shifts in the mean luminosities of supernovae (or changes in the amount of interstellar extinction) resul t in dramatic changes in the calculated supernova rates. The rate of c ore-collapse supernovae within 4 kpc of the Sun is calculated to be ap proximately 2.3(H0/75)2 per millennium. This rate is in excellent agre ement with the fact that four such objects are known to have occurred within 4 kpc during the last 2000 years.