arXiv : Diffuse cosmic rays shining in the Galactic center: A novel interpretation of H.E.S.S. and Fermi-LAT gamma-ray data

Gaggero, D.; Urbano, A.; Grasso, D.; Marinelli, A.; Taoso, M.

doi:10.1103/PhysRevLett.119.031101

Published Articles
Report number	arXiv:1702.01124 ; CERN-TH-2017-034
Title	Diffuse cosmic rays shining in the Galactic center: A novel interpretation of H.E.S.S. and Fermi-LAT gamma-ray data
Related title	Diffuse cosmic rays shining in the Galactic center: A novel interpretation of H.E.S.S. and Fermi-LAT gamma-ray data
Author(s)	Gaggero, D. (U. Amsterdam, GRAPPA) ; Grasso, D. (INFN, Pisa ; Pisa U.) ; Marinelli, A. (INFN, Pisa ; Pisa U.) ; Taoso, M. (Madrid, IFT) ; Urbano, A. (CERN)
Publication	2017-07-17
Imprint	2017-02-03
Number of pages	5
Note	5 pages, 3 figures, accepted for publication in Physical Review Letters
In:	Phys. Rev. Lett. 119 (2017) 031101
DOI	10.1103/PhysRevLett.119.031101
Subject category	hep-ph ; Particle Physics - Phenomenology ; astro-ph.HE ; Astrophysics and Astronomy
Abstract	We present a novel interpretation of the $\gamma$-ray diffuse emission measured by Fermi-LAT and H.E.S.S. in the Galactic center (GC) region and the Galactic ridge (GR). In the first part we perform a data-driven analysis based on PASS8 Fermi-LAT data: we extend down to few GeV the spectra measured by H.E.S.S. and infer the primary cosmic-ray (CR) radial distribution between 0.1 and 3 TeV. In the second part we adopt a CR transport model based on a position-dependent diffusion coefficient. Such behavior reproduces the radial dependence of the CR spectral index recently inferred from the Fermi-LAT observations. We find that the bulk of the GR emission can be naturally explained by the interaction of the diffuse steady-state Galactic CR sea with the gas present in the Central Molecular Zone. Although our results leave room for a residual radial-dependent emission associated with a central source, the relevance of the large-scale background prevents from a solid evidence of a GC Pevatron.
Copyright/License	arXiv nonexclusive-distrib. 1.0 publication: © 2017-2025 authors (License: CC-BY-4.0)

$The $\gamma$-ray spectrum in the GR region ($| l | < 0.8^\circ$, $| b | < 0.3^\circ$). \Fermi-LAT data, shown here for the first time, and H.E.S.S. data from \cite{Aharonian:2006au} are compared with the contribution of the Galactic CR {\it sea} as computed with the {\it gamma} and {\it base} models discussed in the text. The single power-law best fit of the combined data is also reported. We have subtracted the contribution of point sources from \Fermi-LAT data.$ $Same as Fig.~\ref{fig:spectrum_ridge} but for the {\it pacman} region defined in the text.$ $The CR energy density radial profiles for $E_{CR} > 10~\TeV$, as determined by H.E.S.S. \cite{::2016dhk}, and for $0.1 \le E_{CR} \le 3~\TeV$, as determined here from \Fermi-LAT data, are reported. Those data are compared with the {\it gamma} model predictions (solid lines). The regions of sky used for deriving the data are represented in the inset. The model energy density profiles on Galactic scales are reported in the Supplementary material.$ Show more plots

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