Diffractive interaction and scaling violation in p p ---> pi0 interaction and GeV excess in galactic diffuse gamma-ray spectrum of EGRET
Oct, 200435 pages
Published in:
- Astrophys.J. 620 (2005) 244-256
e-Print:
- astro-ph/0410617 [astro-ph]
DOI:
Report number:
- SLAC-PUB-10819
Experiments:
Citations per year
Abstract: (arXiv)
We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in the Galactic ridge environment. The calculation includes the diffractive pp interaction and incorporates the Feynman scaling violation for the first time. Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV range (GeV Excess) in the EGRET Galactic diffuse spectrum above the prediction based on experimental pp->pi^0 cross-sections and the Feynman scaling hypothesis. We show, in this work, that the diffractive process makes the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in power-law index, and, that the scaling violation produces 30-80% more pi^0 than the scaling model for incident proton energies above 100GeV. Combination of the two can explain about a half of the GeV Excess with the local cosmic proton (power-law index ~2.7). The excess can be fully explained if the proton spectral index in the Galactic ridge is a little harder (~0.2 in power-law index) than the local spectrum. Given also in the paper is that the diffractive process enhances e^+ over e^- and the scaling violation gives 50-100% higher p-bar yield than without the violation, both in the multi-GeV range.Note:
- 35 pages, 11 figures, to appear in Astrophysical Journal Report-no: SLAC-PUB-10819
- cosmic rays
- diffuse radiation
- gamma rays: observations
- gamma rays: theory
- ISM: general
- p: cosmic radiation
- photon: cosmic radiation
- cosmic radiation: energy spectrum
- p p: inclusive reaction
- anti-p p: inclusive reaction
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