Explosion energies, nickel masses and distances of Type II plateau supernovae

The hydrodynamical modelling of Type Il plateau supernova (SNIIP) light curves predicts a correlation between three observable parameters (plateau duration, absolute magnitude and photospheric velocity at the middle of the plateau) on the one hand, and three physical parameters (explosion energy E, mass of the envelope expelled M and pre-supernova radius R) on the other. The correlation is used, together with adopted distances from the expanding photosphere method, to estimate E, M and R for a dozen well-observed SNIIP. For this set of supernovae, the resulting value of E varies within a factor of 6 (0.5 less than or similar to E/10(51) erg less than or similar to 3), whereas the envelope mass remains within the limits 10 less than or similar to M/M-. less than or similar to 30. The pre-supernova radius is typically 200-600 R-., but can reach greater than or similar to 1000 R-. for the brightest supernovae (e.g. SN 1992am). A new method of determining the distance of SNIIP is proposed. It is based on the assumption of a correlation between the explosion energy E and the Ni-56 mass required to power the post-plateau light curve tail through Co-56 decay. The method is useful for SNIIP with well-observed bolometric light curves during both the plateau and radioactive tail phases. The resulting distances and future improvements are discussed.