Fermi LAT Observation of Diffuse Gamma-Rays Produced through Interactions Between Local Interstellar Matter and High Energy Cosmic Rays

• Published in: The Astrophysical journal 2012-03, Vol.703 (2)
• Main Authors: Abdo, A.A., /Naval Research Lab, Wash., D.C. /Federal City Coll, Ackermann, M., /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept, Ajello, M., Atwood, W.B., /UC, Santa Cruz, Axelsson, M., /Stockholm U. /Stockholm U., OKC, Baldini, L., /INFN, Pisa, Ballet, J., /DAPNIA, Saclay, Barbiellini, G., /INFN, Trieste /Trieste U., Bastieri, D., /INFN, Padua /Padua U., Baughman, B.M., /Ohio State U., Bechtol, K., Bellazzini, R., Berenji, B., Bloom, E.D., Bonamente, E., /INFN, Perugia /Perugia U., Borgland, A.W., Bregeon, J., Brez, A., Brigida, M., /Bari U. /INFN, Bari, Bruel, P., /Ecole Polytechnique, Burnett, T.H., /Washington U., Seattle /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /IASF, Milan /Milan Polytechnic /Royal Inst. Tech., Stockholm /Stockholm U., OKC /DAPNIA, Saclay /INFN, Perugia /Perugia U. /NASA, Goddard /Naval Research Lab, Wash., D.C. /George Mason U. /NASA, Goddard /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Montpellier U. /Stockholm U. /Stockholm U., OKC /Royal Inst. Tech., Stockholm /ASDC, Frascati /Naval Research Lab, Wash., D.C. /INFN, Trieste /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /CENBG, Gradignan /CENBG, Gradignan /Montpellier U. /Bari U. /INFN, Bari /Ecole Polytechnique /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /INFN, Trieste /Hiroshima U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Bari U. /INFN, Bari /INFN, Bari, /more authors
• Format: Article
• Language: English
• Subjects: 08 HYDROGEN; Astrophysics,ASTRO; CLOUDS; COMPTON EFFECT; COSMIC RADIATION; EMISSIVITY; HYDROGEN; NUCLEI; PHOTONS; POINT SOURCES; SOLAR SYSTEM; SPECTRA; TELESCOPES
• ISSN: 0004-637X; 1538-4357

Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse {gamma}-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200{sup o} to 260{sup o} and latitude |b| from 22{sup o} to 60{sup o}) 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 {+-} 0.05) x 10{sup -26} photons s{sup -1}sr{sup -1} H-atom{sup -1} and (0.66 {+-} 0.02) x 10{sup -26} photons s{sup -1}sr{sup -1} H-atom{sup -1} above 100 MeV and above 300 MeV, respectively, with an additional systematic error of {approx}10%. The differential emissivity from 100 MeV to 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 {approx}10%.