http://arxiv.org/abs/1702.04362
The X-ray light curves of the early afterglow phase from gamma-ray bursts present a puzzling diversity, including flares. The origin of these flares is still debated, and often associated with a late activity of the central engine. We discuss an alternative scenario where the central engine remains short-lived and flares are produced by the propagation of a long-lived reverse shock in a stratified ejecta. We use a set of one-dimensional ultrarelativistic hydrodynamic simulations with different initial internal structure in the gamma-ray burst ejecta. We use them to extract bolometric light curves and compare them with a previous study based on a simplified ballistic model. We find a good agreement between the two approaches, with similar slopes and variability in the light curves, but identify several weaknesses in the ballistic model: the density is underestimated in the shocked regions, and more importantly, late shock reflections are not captured. With the accurate dynamics provided by our hydrodynamic simulations, we confirm that internal shocks in the ejecta lead to the formation of dense shells. The interaction of a long-lived reverse shock with these dense shells then produces bright flares in the bolometric light curve, with arrival times, shapes, and duration in agreement with the observed properties of X-ray flares in GRB afterglows.
A. Lamberts and F. Daigne
Thu, 16 Feb 17
1/45
Comments: Submitted to MNRAS, comments welcome
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