Detections of Gamma-Rays from Globular Clusters ESO 452-SC11, NGC 6380, Palomar 6 and UKS 1 with Fermi-LAT

Abstract

The events from 157 globular clusters (GCs) are analyzed by using 12 yr long-term Pass 8 data from Fermi Large Area Telescope. Besides the 34 GCs reported in previous literatures, four additional GCs (ESO 452-SC11, NGC 6380, Palomar 6 and UKS 1) in the Milky Way are detected as gamma-ray GC candidates. Especially for UKS 1, these are known as the faintest GCs in long-wavelength bands. Further data analysis has been performed for the four GCs. While no pulsars are determined in radio and/or X-ray wavelengths so far, their gamma-ray pulsation emissions are not found, and no significant gamma-ray flux variability is detected. The numbers of MSPs within the four GCs are estimated based on the assumption that the MSPs within each GC emit similar amounts of gamma-rays. The gamma-ray results reported here could help us better understand the nature of gamma-ray emission origins for GCs.