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Session 43 - Gamma-ray Burst Counterparts and Afterglows.
Display session, Tuesday, June 09
Atlas Ballroom,
We present two-dimensional hydrodynamical calculations of the ``collapsar'' model for gamma-ray bursts using a PPM hydrodynamics code and appropriate nuclear, neutrino and accretion disc physics. The collapsar model occurs in rotating massive stars which fail to eject all of their envelopes in a supernova explosion. The remaining material collapses onto the stellar core, forming a black hole which continues to accrete matter. The infalling material forms a disc around the black hole which heats due to viscous dissipation and emits neutrinos. For example, the collapse of the inner 8\,M_ødot of a 25\,M_ødot star with specific angular momentum of \sim\!10^17 cm^2\,s^-1 forms an accretion disc with densities of \sim\!10^10\,g\,cm^-3, temperatures of \sim\!5\!\times\!10^10\,K, and a resultant peak integrated neutrino luminosity of nearly 10^52\,erg\,s^-1. These neutrinos annihilate along the polar axis to form a photon/e^+\!e^-\,pair plasma, which is posited to expand, break through the stellar mantle and drive a beamed gamma ray burst. Other systems containing specific angular momentum in the range 10^16\!-\! 10^18\,cm^2\,s^-1 which will produce similar black hole accretion disc configurations include the merger of black hole--white dwarf and black hole--red giant binaries. This model predicts large amounts of mildly relativistic ejecta in addition to the ultra-relativistic material producing the gamma rays. The mildly relativistic material may have important implications for afterglows in non-gamma-ray wavelengths.
