A study of the Type II-P supernova 2003gd in M74

Abstract

We present photometric and spectroscopic data of the type II-P supernova\n2003gd, which was discovered in M74 close to the end of its plateau phase. SN\n2003gd is the first type II supernova to have a directly confirmed red\nsupergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P\nsupernova, and estimate an explosion date of 18th March 2003. We determine a\nreddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different\nmethods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc,\n7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the\nStandardised Candle Method (SCM), for type II supernovae, and the latter two\nusing the Brightest Supergiants Method (BSM). When combined with existing\nkinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc.\nSN 2003gd was found to have a lower tail luminosity compared to other\n``normal'' type II-P SNe bringing into question the nature of this supernova.\nWe present a discussion concluding that this is a ``normal'' type II-P\nsupernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.\n