Visual spectra of hypernova in GRB 030329

Series of VLT-FORS-spectra, showing the spectral evolution of the hypernova (designated SN 2003dh) underlying the gamma-ray burst GRB 030329 (black curves). The red-dotted spectra are those of an earlier, nearby hypernova, SN 1998bw, observed with various ESO telescopes. The elapsed time (days in the rest frame of the object) since the explosion is indicated. There is a striking similarity between the spectra of the two hypernovae, also in their evolution with time. This allowed a precise dating of the explosion of the hypernova underlying GRB 030329.