- Fermi LAT Observation of Diffuse Gamma-Rays Produced Through Interactions between Local Interstellar Matter and High Energy Cosmic Rays doi link

Author(s): Abdo A. A., Ackermann M., Ajello M., B. Atwood W., Axelsson M., Baldini L., Ballet J., Barbiellini G., Bruel P., Casandjian J.M., Cohen-Tanugi J., Dumora D., Farnier C., Fegan S.J., Giebels B., Grenier I.A., Grondin M.-H., Guillemot L., Guiriec Sylvain, Knödlseder J., Lemoine-Goumard M., Lott B., Nuss E., Parent D., Piron F., Reposeur T., Sanchez D., Smith D.A., Starck J.-L., Vilchez N.

(Article) Published: The Astrophysical Journal / The Astrophysical Journal Letters, vol. 703 p.1249-1256 (2009)
Links openAccess full text : arxiv

Ref HAL: in2p3-00429043_v1
Ref Arxiv: 0908.1171
DOI: 10.1088/0004-637X/703/2/1249
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
94 citations

Observations by the Large Area Telescope (LAT) on the \textit{Fermi} mission of diffuse $\gamma$-rays in a mid-latitude region in the third quadrant (Galactic longitude $l$ from $200\arcdeg$ to $260\arcdeg$ and latitude $| b |$ from $22\arcdeg$ to $60\arcdeg$) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of $\gamma$-ray point sources and inverse Compton scattering are estimated and subtracted. The residual $\gamma$-ray intensity exhibits a linear correlation with the atomic gas column density in energy from 100 MeV to 10 GeV. The measured integrated $\gamma$-ray emissivity is $(1.63 \pm 0.05) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ and $(0.66 \pm 0.02) \times 10^{-26} {\rm photons s^{-1} sr^{-1} H\mathchar`-atom^{-1}}$ above 100 MeV and above 300 MeV, respectively, with additional systematic error of $\sim 10%$. The differential emissivity in 100 MeV--10 GeV agrees with calculations based on cosmic ray spectra consistent with those directly measured, at the 10% level. The results obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar system in regions studied are close to the local interstellar spectra inferred from direct measurements at the Earth within $\sim 10%$.