The influence of inverse Compton scattering on GRB afterglows: one possible way to flatten and steepen the light curves

The fireball model of gamma-ray bursts predicted that when the energetic bl ast wave encountered the surrounding medium, there will be afterglow emissi on, and the subsequent afterglow observations appeared to confirm this pred iction. In this simplest fireball model, the electrons have been accelerate d to a power law energy distribution in a relativistic blast wave, then the y give afterglow emission through synchrotron radiation. Up to now synchrot ron radiation is believed to be the main mechanism of GRB emission, however , here we will show that under some circumstances, the inverse Compton scat tering (ICS) may play an important role, and can change the light curves of GRB afterglows. Here we investigate the effects of ICS in the relativistic case (the surrounding medium density rho proportional to r(-2)) and in the non-relativistic case (for both rho = constant and rho proportional to r(- 2)). We find that in the relativistic case the effect of ICS is usually imp ortant, while in the non-relativistic case, this effect is usually unimport ant, unless the surrounding medium density is very high. We show that if IC S is important, then it can flatten and steepen the light curves of GRB aft erglows, and this may provide the explanation for some afterglow observatio ns.