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Volume 312 - 7th International Fermi Symposium (IFS2017) - Session Stellar Sources (galactic and extragalactic)
Reexamining the gamma-ray properties of globular clusters
K. Oh,* C.Y. Hui
*corresponding author
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Supplementary files
Published on: 2017 December 12
We have re-examined the properties of $\gamma-$ray emitting globular clusters (GCs) with the data obtained by Fermi Large Area Telescope in the past nine years. With an updated sample of 19 $\gamma-$ray GCs, we have performed a statistical analysis in the framework set by Hui et al. (2011) \cite{hui}. We confirm that the correlation between the $\gamma-$ray luminosities $L_{\gamma}$ and the metalicity [Fe/H] is as significant as that between $L_{\gamma}$ and the two-body encounter frequencies $\Gamma_{c}$. Correlations between $L_{\gamma}$ and the energy densities of the soft photon field $u_{\rm optical}$/$u_{\rm IR}$ at location of the GCs have also been confirmed. With a two-dimensional regression analysis, we have revised the fundamental planes of $\gamma-$ray GCs which relate $L_{\gamma}$, [Fe/H]/$\Gamma_{c}$ and $u_{\rm optical}$/$u_{\rm IR}$. The updated relations based on can provide better prediction of the $\gamma-$ray properties of GCs and support the scenario that the $\gamma-$ray emission is originated from the inverse Compton scattering (ICS) between the pulsar wind and the ambient soft photon fields.
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