Anisotropic inverse Compton scattering in the Galaxy

Abstract

The inverse Compton scattering of interstellar photons off cosmic-ray electrons seems to play a more important role in the generation of diffuse emission from the Galaxy than thought before. The background radiation field of the Galaxy is highly anisotropic since it is dominated by the radiation from the Galactic plane. An observer in the Galactic plane thus sees mostly head-on scatterings even if the distribution of the cosmic-ray electrons is isotropic. This is especially evident when considering inverse Compton scattering by electrons in the halo, i.e. the diffuse emission at high Galactic latitudes. We derive formulas for this process and show that the anisotropy of the interstellar radiation field has a significant effect on the intensity and angular distribution of the Galactic diffuse gamma rays, which can increase the high-latitude Galactic gamma-ray flux up to 40%. This effect should be taken into account when calculating the Galactic emission for extragalactic background estimates.

11 pages including 16 ps-figures, latex2e, uses emulateapj.sty (ver. of 11 May 1998, included), graphicx.sty, timesfonts.sty. Minor changes. Final version accepted for publication in The Astrophysical Journal (vol. 528, Jan. 1, 2000 issue - tentatively). More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.html

References in corpus (6)

• Propagation of cosmic-ray nucleons in the Galaxy
• Production and propagation of cosmic-ray positrons and electrons
• EGRET Observations of the Extragalactic Gamma Ray Emission
• Electron acceleration in SNR and diffuse gamma-rays above 1 GeV
• Modelling cosmic rays and gamma rays in the Galaxy
• The Galactic contribution to high latitude diffuse gamma-ray emission

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