PoS - Proceedings of Science
Volume 395 - 37th International Cosmic Ray Conference (ICRC2021) - GAD - Gamma Ray Direct
The role of unresolved PWNe to the gamma-ray diffuse emission at GeV
G. Pagliaroli*, V. Vecchiotti and F. Villante
Full text: pdf
Pre-published on: July 04, 2021
Published on: March 18, 2022
We discuss the implications of the TeV galactic Pulsar Wind Nebulae (PWNe) population observed by HESS Galactic Plane Survey (HGPS) for the interpretation of Fermi-LAT data in the GeV domain.
We show that consistency among HGPS and 3FGL catalogs requires that the average ratio $R_\Phi =\Phi_{\rm GeV}/\Phi_{\rm TeV}$, where $\Phi_{\rm GeV}$ ($\Phi_{\rm TeV}$) is the integrated gamma-ray flux emitted by sources in the range 1-100 GeV (1-100 TeV) probed by Fermi-LAT (HESS), is $R_\Phi = 500-1000$.
Considering that the average spectral index of observed sources at TeV energies is $\beta_{\rm TeV} = 2.3$, the required value for $R_\Phi$ can be only obtained by assuming that sources have spectral break below 1 TeV and harder emission spectrum with $\beta_{\rm GeV} < 2$ in the GeV domain.
Such spectral shapes are well compatible with the expected gamma-ray emission in young PWNe due to Inverse Compton scattering of high-energy electrons on background radiation fields.
Finally, we show that a relevant fraction of the TeV source population cannot be resolved by Fermi-LAT in the GeV domain.
We suggest that unresolved PWNe can provide a not negligible contribution to the large-scale diffuse emission observed by Fermi-LAT, possibly explaining the spectral hardening of this component toward the galactic center reported by Gaggero et al. 2018, Yang et al. 2016, Acero et al. 2016.
DOI: https://doi.org/10.22323/1.395.0671
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