GRB Jets with Time Variable Central Engines

Details GRB Jets with Time Variable Central Engines GRB Jets with Time Variable Central Engines

Jan 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21335203m&link_type=abstract

American Astronomical Society, AAS Meeting #213, #352.03; Bulletin of the American Astronomical Society, Vol. 41, p.492

Astronomy and Astrophysics

Astronomy

Scientific paper

We study the long-term evolution of relativistic jets in collapsars and examine the effects of time variable energy input on the subsequent gamma ray bursts. We carry out a series of high-resolution simulations of a jet propagating through a stellar envelope in 2D cylindrical coordinates using the FLASH relativistic hydrodynamics module. We carry out a series of simulations of central engines that vary on long time periods, comparable to the breakout time of the jet, short time periods (0.1s) much less than the breakout time, and that decay as a powerlaw at late times.
Long period simulations show the opening angle of the jet rapidly adjusts to changes in input energy, in about 0.1s. For short period variability, the structure of the jet is not significantly effected by changes of the central engine output, but the signature of these changes is clearly visible in the energy flux seen by an observer. Short period changes are preserved from the central engine to well outside the star, indicating that short timescale fluctuation seen in prompt GRB emission can be due to central engine activity and will reflect the history of that activity.
Models with a decaying energy input have a constant opening angle at late times. This is significant because it allows energy to escape from the central engine to a large radius even with a small energy input at late times, indicating that the central engine could be responsible for the shallow decay seen in X-ray afterglow lightcurves and for X-ray flares. A simulation of a flare from the central engine during the decay phase produces a flare of energy with a sharp rise and decay that is not significantly modified by passing through the stellar envelope.

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