THE SPECTRAL FEATURES OF GAMMA-RAY BURSTS AT LOWER AND HIGHER ENERGY COMPONENTS - A POSSIBLE WAY TO DISTINGUISH BETWEEN COSMOLOGICAL AND GALACTIC ORIGINS OF GAMMA-RAY BURSTS

The isotropic and inhomogeneous distribution of gamma-ray burst source s (GRBs) detected by the Burst and Transient Source Experiment (BATSE) suggests that the GRBs are located either at cosmological distances o r in an extended Galactic halo. Both models predict that the sudden re lease of a huge amount of energy will result in a foreball, and the in teraction between fireball and interstellar medium can produce non-the rmal gamma-ray emission. In this paper we discuss the spectral feature s of GRBs at lower and higher energy bands based on the shock model pr oposed by Meszaros & Rees. We find that for the cosmological model, th e optical flash is nearly impossible to observe since the synchrotron self-absorption frequency is always above similar to 10(15) Hz, but th e TeV emission due to inverse Compton scattering (ICS) is possible to detect if the absorption by the intergalactic radiation field is small . For the Galactic model, the situation is just the opposite; both the self-absorption frequency and the efficiency of the ICS are lower tha n those in the cosmological model. We suggest that this may provide a way to distinguish between Galactic and cosmological origin of GRBs.