TIME DELAY OF CASCADE RADIATION FOR TeV BLAZARS AND THE MEASUREMENT OF THE INTERGALACTIC MAGNETIC FIELD

Recent claims that the strength B-IGMF of the intergalactic magnetic field (IGMF) is greater than or similar to 10(-15) G 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 greater than or similar to 2(B-IGMF/10(-18)G)(2)/(E/10 GeV)(2) yr for an IGMF coherence length approximate to 1 Mpc, where E is the measured photon energy. Restricting TeV activity of 1ES 0229+200 to approximate to 3-4 years during which the source has been observed leads to a more robust lower limit of B-IGMF greater than or similar to 10(-18) G, which can be larger by an order of magnitude if the intrinsic source flux above approximate to 5-10 TeV from 1ES 0229+200 is strong.