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J.C. Wheeler, P. Hoeflich, L. Wang (Department of Astronomy; University of Texas)
The recent discovery of the unusual supernova SN1998bw and its apparent correlation with the gamma-ray burst GRB 980425 has raised new issues concerning both the GRB and SNe. SN1998bw was unusually bright at maximum light and expansion velocities were large making SN1998bw a possible candidate for a ``hypernova" with explosion energies exceeding 1052 erg. We show that the light curve of SN1998bw can be understood as the result of an aspherical explosion along the rotational axis of a basically spherical, non-degenerate C/O core of a massive star with an explosion energy of 2 \times 1051 erg, a total ejecta mass of 2 Mo, and a 56Ni mass of 0.2M\odot if it is seen from high inclinations with respect to the plane of symmetry. In this model, the high expansion velocities are a direct consequence of the aspherical explosion which, in turn, produces oblate iso-density contours. This suggests that the fundamental core-collapse explosion process itself is strongly asymmetric.