paper

Optical Emission from Aspherical Supernovae and the Hypernova SN 1998bw

arXiv:astro-ph/0511389 · doi:10.1086/504581

Abstract

A fully 3D Monte Carlo scheme is applied to compute optical bolometric light curves for aspherical (jet-like) supernova explosion models. Density and abundance distributions are taken from hydrodynamic explosion models, with the energy varied as a parameter to explore the dependence. Our models show initially a very large degree ( depending on model parameters) of boosting luminosity toward the polar () direction relative to the equatorial () plane, which decreases as the time of peak is approached. After the peak, the factor of the luminosity boost remains almost constant () until the supernova enters the nebular phase. This behavior is due mostly to the aspherical Ni distribution in the earlier phase and to the disk-like inner low-velocity structure in the later phase. Also the aspherical models yield an earlier peak date than the spherical models, especially if viewed from near the z-axis. Aspherical models with ejecta mass $\sim 10\Msun$ are examined, and one with the kinetic energy of the expansion ergs and a mass of Ni $\sim 0.4\Msun$ yields a light curve in agreement with the observed light curve of SN 1998bw (the prototypical hyper-energetic supernova). The aspherical model is also at least qualitatively consistent with evolution of photospheric velocities, showing large velocities near the z-axis, and with a late-phase nebular spectrum. The viewing angle is close to the z-axis, strengthening the case for the association of SN 1998bw with the gamma ray burst GRB980425.

Accepted by the Astrophysical Journal. 28 pages, 14 figures

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