The Type Ic Hypernova SN 2003dh/GRB 030329

The spectra of SN 2003dh, identified in the afterglow of GRB030329, aremodeled using radiation transport codes. It is shown that SN 2003dh had a highexplosion kinetic energy ($\sim 4 \times 10^{52}$ erg in spherical symmetry),making it one of the most powerful hypernovae observed so far, and supportingthe case for association between hypernovae and Gamma Ray Bursts. However, thelight curve derived from fitting the spectra suggests that SN 2003dh was not asbright as SN 1998bw, ejecting only $\sim 0.35\Msun$ of \Nifs. The spectra of SN2003dh resemble those of SN 1998bw around maximum, but later they look morelike those of the less energetic hypernova SN 1997ef. The spectra and theinferred light curve can be modeled adopting a density distribution similar tothat used for SN 1998bw at $ v > 25,000$\kms but more like that of SN 1997ef atlower velocities. The mass of the ejecta is $\sim 8\Msun$, somewhat less thanin the other two hypernovae. The progenitor must have been a massive star ($M\sim 35-40\Msun$), as for other hypernovae. The need to combine differentone-dimensional explosion models strongly indicates that SN 2003dh was anasymmetric explosion.Comment: 11 pages, 1 table and 5 figures. To appear in the Astrophysical Journal (Letters). Revised version taking referee's comments into account, minor change