Gamma-Ray Burst Light Curves—Another Clue on the Inner Engine

The nature of the `inner engine' that accelerate and collimate therelativistic flow at the cores of GRBs is the most interesting current puzzleconcerning GRBs. Numerical simulations have shown that the internal shocks'light curve reflects the activity of this inner engine. Using a simple analytictoy model we clarify the relations between the observed $ \gamma $-rays lightcurve and the inner engine's activity and the dependence of the light curves onthe inner engine's parameters. This simple model also explains the observedsimilarity between the observed distributions of pulses widths and theintervals between pulses and the correlation between the width of a pulse andthe length of the preceding interval. Our analysis suggests that thevariability in the wind's Lorentz factors arises due to a modulation of themass injected into a constant energy flow.Comment: 5 pages submitted to Ap. J. Let