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SN 1998bw/GRB 980425: Hypernova or Aspherical Explosion?

P. Hoeflich·J. C. Wheeler·L. Wang
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Abstract

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 10^{52} 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 2E51 erg, a total ejecta mass of 2 M_o, and a 56Ni mass of 0.2M_o 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.

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P. Hoeflich, J. C. Wheeler, L. Wang. 1998-07-31. SN 1998bw/GRB 980425: Hypernova or Aspherical Explosion?. https://arxiv.org/abs/astro-ph/9807345

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