On core-collapse supernovae in normal and in Seyfert galaxies

This paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio S between the number of Type Ib-Ic and of Type H supernovae. We estimate S independently for all normal and Seyfert galaxies whose radial velocity is less than or equal to 14 000 km s(-1), and which had at least one supernova event recorded in the Asiago catalogue from 1986 January to 2000 August. We find that the ratio S is approximate to 0.23 +/- 0.05 in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter initial mass function and an average binary rate approximate to50 per cent. On the contrary, Seyfert galaxies exceed the ratio S in normal galaxies by a factor approximate to4 at a confidence level; greater than or similar to20sigma. A caveat is that the numbers for Seyferts are still small (six of Type lb-Ic and six of Type H supernovae discovered as yet). Assumed to be real, this excess of Type We supernovae may indicate a burst of low-age star formation (tau less than or similar to 20 Myr), a high incidence of binary systems in the inner regions (r less than or similar to 0.4R(25)) of Seyfert galaxies, or a top-loaded mass function.