Delayed MeV–GeV Gamma-Ray Photons in Gamma-Ray Bursts: An Effect of Electromagnetic Cascades of Very High Energy Gamma Rays in the Infrared/Microwave Background

Abstract

We show that the electromagnetic cascade of very high energy gamma-rays from gamma-ray bursts in the IR/microwave background will produce delayed MeV--GeV photons. Monte Carlo simulations have been performed to study this process. The distance of GB 940217 is estimated to be not less than 120 Mpc using our model, which supports a cosmological origin for this source. We also show that the time delays of gamma-ray photons are inversely proportional to their energy. Our model does not require the presence of intergalactic magnetic fields.