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CfA theory seminar

CfA theory seminar

Fri, Dec 5
12:30pm, Phillips Auditorium at CfA

Weiqun Zhang (UC Santa Cruz)

Numerical Simulations of Relativistic Jets in Collapsars

In this talk, I report numerical simulations of relativistic jets in
collapsars.  Such jets are believed to give rise to outbursts of
high-energy emission known as gamma-ray bursts.  The propagation and
break out of the jets are examined in multi-dimensional numerical
simulations using a special relativistic hydrodynamics code.  During
its propagation, the jet is collimated by the passage through the
stellar mantle.  Interaction of the jet with the star and its own
cocoon also causes mixing that sporadically decelerates the flow.  As
it erupts, the highly relativistic jet core is surrounded by a cocoon
of less energetic, but still moderately relativistic ejecta that
expands and becomes visible at larger polar angles.  We predict a
distribution of energy and Lorentz factor with viewing angle in the
jet beam and its cocoon.  These imply that what is seen may vary
greatly with viewing angle.  In particular, we predict the existence
of a large number of low energy GRBs with mild Lorentz factors that
may be related to GRB 980425/SN 1998bw and to the recently recognized
cosmological X-ray flashes.