Gamma-ray burst light curves in the relativistic turbulence and relativistic subjet models

Abstract

Randomly oriented relativistic emitters in a relativistically expanding shell provide an alternative to internal shocks as a mechanism for producing gamma-ray bursts' variable light curves with efficient conversion of energy to radiation. In this model, the relativistic outflow is broken into small emitters moving relativistically in the outflow's rest frame. Variability arises because an observer sees an emitter only when its velocity points toward him so that only a small fraction of the emitters is seen by a given observer. Significant relativistic random motion requires that a large fraction of the overall energy is converted to random kinetic energy and is maintained in this form. While it is not clear how this is achieved, we explore here, using two toy models, the constraints on parameters required to produce light curves comparable to the observations. We find that a tight relation between the size of the emitters, and the bulk and random Lorentz factors is needed and that the random Lorentz factor determines the variability. While both models successfully produce the observed variability there are several inconsistencies with other properties of the light curves. Most of which, but not all, might be resolved if the central engine is active for a long time, producing a number of shells, resembling to some extent the internal shocks model.

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