2004ApJ...604..306W

It has been suggested that electromagnetic cascade of very high-energy gamma-rays from gamma-ray bursts (GRBs) in the infrared/microwave background can produce delayed MeV-GeV photons. This delay could be caused by the angular spreading effect of the scattered microwave photons or deflection of the secondary pairs due to the intergalactic magnetic field. Very high-energy TeV photons of GRBs could be produced by a few mechanisms including the proton-synchrotron radiation and electron inverse Compton emission from GRB internal shocks as well as external shocks. We suggest that the information provided by the delayed emission could give constraints on models for TeV gamma-rays. A more accurate calculation of the delayed time caused by the angular spreading effect is presented by considering recent observations of the extragalactic infrared background and the theoretical high-redshift infrared background. We also suggest that the dependence of the maximum time delay of scattered photons on their energies, if determined by future GLAST detector, could differentiate the two mechanisms causing the time delay.