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 sources (GRBs) detected by the Burst and Transient Source Experiment (BATSE) suggests that the GRBs are located either at cosmological distances or in an extended Galactic halo. Both models predict that the sudden release of a huge amount of energy will result in a foreball, and the interaction between fireball and interstellar medium can produce non-thermal gamma-ray emission. In this paper we discuss the spectral features of GRBs at lower and higher energy bands based on the shock model proposed by Meszaros & Rees. We find that for the cosmological model, the optical flash is nearly impossible to observe since the synchrotron self-absorption frequency is always above similar to 10(15) Hz, but the 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 than those in the cosmological model. We suggest that this may provide a way to distinguish between Galactic and cosmological origin of GRBs.