Model predictions for the MeV-to-TeV emission of GRBs.

We estimate the emission from the X-ray to the TeV energy bands in the context of different models, with particular regard to Internal and External shocks with synchrotron and self synchrotron Compton radiation. Model predictions can be tested with observations by Swift (at low energies) and by AGILE, GLAST and Cherenkov telescopes (at high energies) during the prompt, and X-ray flare phases of gamma-ray bursts (GRBs). For the prompt emission we find that the detectability of the SSC emission improves for higher values of the fireball Lorentz factor and of the bursts temporal variability and that the best candidate bursts for high energy detection will be those with the peak energy close to the lower value of the Swift BAT energy band, i.e. X-ray flash gamma-ray bursts. However, due to the source optical thickness high energy emission during the prompt phase of GRBs is difficult to detect by Cherenkov telescopes. For the flares we discuss them in the framework of the late internal shock (LIS) and the delayed external shock (DES) scenario. In both the models the mechanism responsible for X-ray flares is synchrotron emission and X-ray flare photons are expected to be up-scattered by Inverse Compton thus producing high energy flares. We show that the LIS and the DES models predict different properties for the high energy emission component. In the context of the LIS the peak of the high energy flare is expected to be at lower energies with respect to that predicted by the DES scenario, i.e. in the MeV band for internal shocks and in the GeV-TeV band for the external shock. In addition, the LIS model predicts an anti-correlation between the flare temporal variability and the peak energy of the related IC component. A detailed temporal analysis of flare light curves is mandatory to understand the physics of the flares and to check the LIS model. Simultaneous observations by Swift in the X-ray band, and by AGILE, GLAST and MAGIC at high energies, could play an important role to test model predictions, and thus to constrain the origin of flares and the physics of the central engine.