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 풮 between the number of Type Ib–Ic and of Type II supernovae. We estimate 풮 independently for all normal and Seyfert galaxies whose radial velocity is ≤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 풮 is ≈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 ≈50 per cent. On the contrary, Seyfert galaxies exceed the ratio 풮 in normal galaxies by a factor ≈4 at a confidence level ≳2σ. A caveat is that the numbers for Seyferts are still small (six of Type Ib–Ic and six of Type II supernovae discovered as yet). Assumed to be real, this excess of Type Ib/c supernovae may indicate a burst of low-age star formation(τ≲20 Myr), a high incidence of binary systems in the inner regions (r≲0.4R25) of Seyfert galaxies, or a top-loaded mass function.