New BVRI photometry and optical spectroscopy of the Type IIp supernova 2004dj in NGC 2403 , obtained during the first year since discovery , are presented .
The progenitor cluster , Sandage 96 , is also detected on pre-explosion frames .
The light curve indicates that the explosion occured about 30 days before discovery , and the plateau phase lasted about +110 \pm 20 days after that .
The plateau-phase spectra have been modelled with the SYNOW spectral synthesis code using H , Na I , Ti II , Sc II , Fe II and Ba II lines .
The SN distance is inferred from the Expanding Photosphere Method ( EPM ) and the Standard Candle Method ( SCM ) applicable for SNe IIp .
They resulted in distances that are consistent with each other as well as earlier Cepheid- and Tully-Fisher distances .
The average distance , D = 3.47 \pm 0.29 Mpc is proposed for SN 2004dj and NGC 2403 .
The nickel mass produced by the explosion is estimated as \sim 0.02 \pm 0.01 ~ { } M _ { \odot } .
The SED of the progenitor cluster is reanalysed by fitting population synthesis models to our observed BVRI data supplemented by U and JKH magnitudes from the literature .
The \chi ^ { 2 } -minimization revealed a possible ” young ” solution with cluster age T _ { cl } = 8 Myr , and an ” old ” solution with T _ { cl } = 20 - 30 Myr .
The ” young ” solution would imply a progenitor mass M > 20 ~ { } M _ { \odot } , which is higher than the previously detected progenitor masses for Type II SNe .