The 'extragalactic' diffuse gamma ray intensity

We have returned to the problem of the apparently diffuse gamma rays coming from extragalactic space, the energy range being 30 MeV-4 GeV. The return involves the use of somewhat more precise EGRET data (Phase 1 and 2 sky survey) than was used in our earlier work but more particularly a detailed analysis of the Inverse Compton contribution, of Galactic origin. The ensuing extragalactic intensity is significantly lower than hitherto and an interesting consequence is that the spectrum joins rather nicely that estimated recently at lower energies using the COMPTEL instrument. We have also made a rather speculative estimate of the contribution from gamma rays produced in the Giant Galactic Halo which has been claimed to extend to some 100 kpc from the sun. The conclusion is that the truly extragalactic diffuse intensity could be much lower than commonly estimated over a wide energy band. (C) 1997 Elsevier Science B.V.