TP-22

Asymmetric explosions in massive rotating stars

Andrew MacFadyen

The fate of massive (M_ms $\lower .1ex\hbox{\rlap{\raise .6ex\hbox{\hskip .3ex {\ifmmode{\scriptscriptstyl... ... -.4ex{\ifmmode{\scriptscriptstyle \sim}\else {$\scriptscriptstyle\sim$ }\fi}}$ 25 M $_{\scriptscriptstyle \odot}$) rotating stars for which the Type-II supernova mechanism fails to launch a strong explosion is studied by means of 1D and 2D hydrodynamical simulations. In the extreme case (M_ms $\lower .1ex\hbox{\rlap{\raise .6ex\hbox{\hskip .3ex {\ifmmode{\scriptscriptstyl... ... -.4ex{\ifmmode{\scriptscriptstyle \sim}\else {$\scriptscriptstyle\sim$ }\fi}}$ 35 M $_{\scriptscriptstyle \odot}$) a collapsar - a rapidly accreting ( $\dot{M} \approx$ 0.1 M $_{\scriptscriptstyle \odot}$s^-1) stellar mass black hole at the center of a collapsing star - forms promptly. Here we study the case of weak to moderately energetic supernova explosions in rotating stars with extended Hydrogen envelopes. For explosion energies (at infinity) in the range 0.2 - 1.7 $\times 10^{51}$ ergs part of the exploding stellar mantle (0.1 - 5 M $_{\scriptscriptstyle \odot}$) fails to reach terminal escape velocity and accretes onto the central compact object. Accretion rates of 10^-2 - 10^-6 M $_{\scriptscriptstyle \odot}$s^-1 result over timescales of 100 - 100,000 s. Since the accreting gas has sufficient angular momentum to form an accretion disk around the central black hole, a jet engine similar to currently favored GRB engine models forms within an extended stellar envelope. 2D modelling demonstrates the propagation of the ensuing jet-driven explosion through the stellar envelope. The resulting asymmetric explosions have isotropic equivalent energies (4 $\pi dE/d\Omega$) at breakout ranging from 10⁵⁴ ergs at the pole to 10⁵¹ ergs near the equator. Were the stars stripped of their envelopes by mass loss due to a wind or accretion onto a companion, they would be capable of producing long, t $\approx$ 1000 s, GRBs.