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Fermi-LAT observations of the Sagittarius B complex


Yang,  Ruizhi
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;


Aharonian,  Felix A.
Division Prof. Dr. Werner Hofmann, MPI for Nuclear Physics, Max Planck Society;
Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland;
Gran Sasso Science Institute, 7 viale Francesco Crispi, 67100 L’Aquila (AQ), Italy.;

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Yang, R., Jones, D. I., & Aharonian, F. A. (2015). Fermi-LAT observations of the Sagittarius B complex. Astronomy and Astrophysics, 580: A90. doi:10.1051/0004-6361/201425233.

Aims. We use 5 years of Fermi-LAT data towards the Galactic-centre giant molecular cloud complex, Sagittarius B, to test questions of how well-mixed the Galactic component of cosmic rays are and what the level of the cosmic-ray sea in different parts of the Galaxy is. Methods. We use dust-opacity maps from the Planck satellite to obtain independent methods for background subtraction and an estimate for the mass of the region. We then present high-quality spectra of gamma-ray emission from 0.3 to 30 GeV and obtain an estimate of the cosmic-ray spectrum from the region. Results. We obtain an estimate of the mass of the region of $1.5 \pm 0.2 \times 10^7~\rm M_{\odot}$ using the Planck data, which agrees well with molecular-line-derived estimates for the same region. We find the the gamma-ray flux from this region is fitted well with a cosmic-ray spectrum that is the same as is observed locally, with evidence of a small over-density at intermediate (1-10 GeV) energies. Conclusions. We conclude that the gamma-ray and cosmic-ray spectrum in the region can be well-fitted using a local cosmic-ray spectrum.