http://arxiv.org/abs/1907.06061
Context. Measurement of diffuse Galactic gamma-ray flux in the TeV range is difficult for ground-based gamma-ray telescopes because of uncertainties of estimates of background in the telescope field of view. Its detection is also challenging for the space-based telescopes because of low signal statistics. Aims. We characterise the diffuse TeV flux from the Galaxy using decade-long exposure of Fermi Large Area Telescope. Methods. Considering that the level of diffuse Galactic emission in the TeV band approaches the level of residual cosmic ray background, we estimate the residual cosmic ray background in the SOURCEVETO event selection and verify that the TeV diffuse Galactic emission flux is well above the residual cosmic ray background up to high Galactic latitude. Results. We study spectral and imaging properties of the diffuse TeV signal from the Galactic Plane. We find much stronger emission from the inner Galactic Plane, compared to previous HESS telescope measurement. We also find significant discrepancies in the measurement of Galactic longitude and latitude profiles of the signal measured by Fermi and HESS. These discrepancies are presumably explained by the fact that regions of background estimate in HESS have non-negligible gamma-ray flux. Comparing Fermi measurements with that of ARGO-YBJ we find better agreement, with a notable exception of Cygnus region, where we find much higher flux (by a factor 1.5). We also measure the TeV diffuse emission spectrum up to high Galactic latitude and show that the spectrum of different regions of the sky have spectral slopes consistent with Gamma = 2.34 +/- 0.04, which is harder than the slope of locally observed spectrum of cosmic rays with energies 10-100 TeV, which produce TeV diffuse emission on their way through the interstellar medium. We discuss possible origin of the hard slope of TeV diffuse emission.
A. A.Neronov and D. D.V.Semikoz
Tue, 16 Jul 19
52/89
Comments: 7 pages, 7 figures