Extending the model of Dawson & Johnson for the observability of supernovae

We construct a Monte Carlo code like that used by Dawson & Johnson to study the observability of Galactic supernovae. In this paper we adopt the Dawson & Johnson model for the distributions of supernova progenitors and dust in the Galaxy, but vary the supernova luminosity functions. Motivated by a paper by Schaefer in which the probable existence of subluminous supernovae is stressed, we consider the observability of a hypothesized population of ultradim supernovae having M-v = -13 and sigma (M-v) = 2. We estimate on the basis of six known Galactic supernovae within the last 1000 years that the number of ultradim supernovae is comparable to the number of 'classical' (luminous) supernovae, and that allowing for the possibility of ultradim supernovae significantly raises the Galactic supernova rate as inferred from the historical record. We also consider the observability of supernovae in this model from the point of view of an external observer, as a function of inclination angle. We find that this particular model is not dusty enough to account by means of extinction for a strong observational selection against the discovery of supernovae in moderately inclined galaxies, and that it predicts the probability distribution of extinction for Type Ia supernovae to be strongly peaked near zero.