10/16/14 SO/NOAO Joint Colloquium Series: Andrew MacFadyen
Andrew MacFadyen, New York University
The Dynamics, Stability and Radiation of GRB Jets
Gamma-rays bursts and their afterglows involve the dynamics of highly relativistic plasma as it is accelerated at the central engine and expands over more than ten orders of magnitude in length scale. I will discuss high resolution studies of GRB jets using a powerful new code (JET) which employs a moving numerical mesh, thus allowing for highly accurate Lagrangian multi-dimensional simulations of relativistic jet dynamics. I will present the first multidimensional simulations of a collapsar jet starting from the center of a massive star, breaking out of the stellar surface, coasting and producing internal then external shocks. Synchrotron light curves computed from the simulation data naturally produce the early steep decay and extended plateau observed in early X-ray light curves. During the deceleration phase I will demonstrate that GRB jets are unstable to the Rayleigh-Taylor instability. This makes the jets turbulent, thus amplifying magnetic fields via small-scale dynamo to values sufficient to explain the synchrotron emission. The Rayleigh-Taylor fingers can also impact the forward shock thus corrugating it with possible implications for the afterglow emission. I will demonstrate fits of theoretical light curves computed from numerical simulations to the observational data.
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