Monitoring of the prompt radio emission from the unusual supernova SN 2004dj in NGC 2403

Supernova SN 2004dj in the nearby spiral galaxy NGC 2403 was detected optically in 2004 July. Peaking at a magnitude of 11.2, this is the brightest supernova detected for several years. Here we present Multi-Element Radio Linked Interferometer Network ( MERLIN) observations of this source, made over a 4 month period, that give a position of R.A. = 07(h)37(m)17(s). 044, decl. = p +65 degrees 35'57.'' 84 (J2000.0). We also present a well-sampled 5 GHz light curve covering the period from 2004 August 5 to December 2. With the exception of the unusual and very close SN 1987A, these observations represent the first detailed radio light curve for the prompt emission from a Type II-P supernova.