Detectability of pair echoes from gamma-ray bursts and intergalactic magnetic fields

High-energy emission from gamma-ray bursts (GRBs) can give rise to pair echoes, i.e., delayed inverse Compton emission from secondary electron-positron pairs produced in photon-photon interactions with intergalac tic background radiation. We investigate the detectability of such emission with modern-day gamma-ray telescopes. The spectra and light curves are calculated for a wide range of parameters, applying the formalism recently developed by Ichiki et al. The flux depends strongly on the unknown magnitude and coherence length of intergalactic magnetic fields, and we delineate the range of field strength and redshift that allow detectable echoes. Relevant uncertainties such as the high-energy cutoff of the primary gamma-ray spectrum and the intensity of the cosmic infrared background are addressed. GLAST and MAGIC may be able to detect pair echo emission from GRBs with redshift ≲1 if the primary spectra extend to ∼10 TeV, offering a unique probe of intergalactic magnetic fields.