Time delay of cascade radiation for TeV blazars and the measurement of the intergalactic magnetic field

Abstract

Recent claims that the strength B IGMF of the intergalactic magnetic field (IGMF) is ≳ 10-15G are based on upper limits to the expected cascade flux in the GeV band produced by blazar TeV photons absorbed by the extragalactic background light. This limit depends on an assumption that the mean blazar TeV flux remains constant on timescales ≳ 2(B IGMF/10-18G)2/(E/10 GeV)2yr for an IGMF coherence length 1Mpc, where E is the measured photon energy. Restricting TeV activity of 1ES 0229+200 to 3-4 years during which the source has been observed leads to a more robust lower limit of B IGMF ≳ 10-18 G, which can be larger by an order of magnitude if the intrinsic source flux above 5-10TeV from 1ES 0229+200 is strong. © 2011. The American Astronomical Society. All rights reserved.