THE SPECTRAL FLATTENING OF THE LOW-ENERGY COMPONENT IN GAMMA-RAY BURSTS

Observations from BATSE show that the spectra of gamma-ray bursts are very wide, which cannot be described by a simple law. The distribution of the peak energy E(p) [defined as the maximum of the E(gamma)(2)N(E (gamma)) spectrum], and of the spectral indices below and above E(p), is wide. In particular, the slope below E(p) lies mainly between 0.5 a nd 1, which is inconsistent with the 4/3 predicted by the simple synch rotron radiation spectrum. Here we discuss the emission model for gamm a-ray bursts based on the shock model proposed by Meszaros & Rees. We find that the synchrotron radiation of relativistic electrons accelera ted by a strong shock, together with the finite lifetime of synchrotro n radiation and the non-uniform magnetic field distribution, can expla in the gamma-ray burst spectra, and the spectral index below the peak energy E(p) can be flattened by the non-uniform magnetic field distrib ution; this flattening is insensitive to the specific form of the magn etic field variance. Furthermore, the peak energy E(p) proportional to Gamma(4) is sensitively dependent on the bulk Lorentz factor.