A GeV-TeV particle component and the barrier of cosmic-ray sea in the Central Molecular Zone

Xiaoyuan Huang,Qiang Yuan,Yi-Zhong Fan

doi:10.1038/s41467-021-26436-z

Abstract

Cosmic rays are important probe of a number of fundamental physical problems such as the acceleration of high and very high energy particles in extreme astrophysical environments. The Galactic center is widely anticipated to be an important cosmic-ray source and the observations of some Imaging Atmospheric Cherenkov Telescopes did successfully reveal a component of TeV-PeV cosmic rays in the vicinity of the Galactic center. Here we report the identification of GeV-TeV cosmic rays in the central molecular zone with the γ-ray observations of the Fermi Large Area Telescope, whose spectrum and spatial gradient are consistent with that measured by the Imaging Atmospheric Cherenkov Telescopes but the corresponding cosmic-ray energy density is substantially lower than the so-called cosmic-ray sea component, suggesting the presence of a high energy particle accelerator at the Galactic center and the existence of a barrier that can effectively suppress the penetration of the particles from the cosmic-ray sea to the central molecular zone.

Highlights

Cosmic rays are important probe of a number of fundamental physical problems such as the acceleration of high and very high energy particles in extreme astrophysical environments
Reference 28 analyzed the data in the central molecular zone (CMZ) region, and concluded that a large fraction of the γ-ray emission measured by H.E.S.S. and Fermi-LAT might originate from the interaction of the diffuse Galactic cosmic rays (CRs) sea with the massive molecular clouds in the CMZ, though the possibility of an additional component cannot be ruled out
The spectral index of the CMZ region is harder by 0.19 ± 0.07 than that predicted in the GALPROP Galactic diffuse emission (GDE) model A33, and the integrated energy flux is (7.05 ± 0.44) × 10−5 MeV cm−2 s−1 from 8 to 500 GeV

Summary

Introduction

Cosmic rays are important probe of a number of fundamental physical problems such as the acceleration of high and very high energy particles in extreme astrophysical environments. Reference 28 analyzed the data in the CMZ region, and concluded that a large fraction of the γ-ray emission measured by H.E.S.S. and Fermi-LAT might originate from the interaction of the diffuse Galactic CR sea with the massive molecular clouds in the CMZ, though the possibility of an additional component cannot be ruled out. In such an analysis, the GCE component, which may play an important role in shaping the result, was not included.

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