Pion decay model of the Tibet-AS γ PeV gamma-ray signal
Abstract
The Tibet-AS γ Collaboration has recently reported a measurement of diffuse γ -ray flux from the outer Galactic disk in the energy range reaching PeV. We complement this measurement with the Fermi/LAT measurement of the diffuse flux from the same sky region and study the pion decay model of the combined Fermi /LA T + Tibet -AS γ spectrum. We find that within such a model the average cosmic-ray spectrum in the outer Galactic disk has the same characteristic features as the local cosmic-ray spectrum. In particular, it experiences a hardening at several hundred GV rigidity and a knee feature in the PV rigidity range. The slope of the average cosmic-ray spectrum above the break is close to the locally observed slope of the helium spectrum γ ≃2.5 , but is harder than the slope of the local proton spectrum in the same rigidity range. Although the combination of Fermi/LAT and Tibet-AS γ data points to the presence of the knee in the average cosmic-ray spectrum, the quality of the data is not yet sufficient for the study of knee shape and cosmic-ray composition.
- Publication:
-
Physical Review D
- Pub Date:
- August 2021
- DOI:
- 10.1103/PhysRevD.104.043010
- arXiv:
- arXiv:2105.00959
- Bibcode:
- 2021PhRvD.104d3010K
- Keywords:
-
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 5 pages, 2 figures