Detectability of Pair Echos from Gamma-Ray Bursts and Intergalactic Magnetic Fields

摘要

High-energy emission from gamma-ray bursts (GRBs) can give rise to pairechos, i.e. delayed inverse Compton emission from secondary $e^{pm}$ pairsproduced in $gamma-gamma$ interactions with intergalactic backgroundradiation. We investigate the detectability of such emission with modern-daygamma-ray telescopes. The spectra and light curves are calculated for a widerange of parameters, applying the formalism recently developed by Ichiki et al.The flux depends strongly on the unknown magnitude and coherence length ofintergalactic magnetic fields, and we delineate the range of field strength andredshift that allow detectable echos. Relevant uncertainties such as thehigh-energy cutoff of the primary gamma-ray spectrum and the intensity of thecosmic infrared background are addressed. GLAST and MAGIC may be able to detectpair echo emission from GRBs with redshift $lesssim 1$ if the primary spectraextend to $sim 10 ~ {m TeV}$.