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

The hydrodynamical modelling of Type II 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 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 ≲E/1051 erg ≲ 3), whereas the envelope mass remains within the limits 10 ≲ M/M⊙ ≲ 30. The pre-supernova radius is typically 200-600 R⊙, but can reach ≳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 56Ni mass required to power the post-plateau light curve tail through 56Co 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