Fermi-LAT Studies of Globular Clusters.
2017 December 12
We analyse 30 Galactic globular clusters ( GC ) located off the Galactic plane, using 8 years of Pass 8 Fermi-LAT data in the range 60 MeV - 300 GeV with the analysis down to lower energy being performed for the first time. We refine the prior detections of 5 GC, 47 Tuc, NGC 6093, NGC 6218, NGC 6752 and NGC 7078. We also detect NGC 6254 for the first time. NGC 6093 and NGC 6218 exhibit flat hard spectra in the range 1 - 10 GeV. The lack of a spectral cut-off between 1-4 GeV in NGC 6093 and NGC 6218, suggests other sources of gamma ray emission apart from millisecond pulsars may be important in these GCs.