SIMBAD references

In this paper, ∼12 yr long-term Pass 8 data from Fermi Large Area Telescope for the 157 globular clusters are carefully re-analyzed. Besides the 31 globular clusters reported in the fourth Fermi Large Area Telescope catalog Data Release 2, NGC 1851 is identified as a gamma-ray emitter and the significant gamma-ray emissions from NGC 6715 and NGC 6723 are detected. Especially NGC 6715 is located at a distance of 26.8 kpc, so far it is the farthest globular cluster detected in gamma-rays. A detailed analysis for these three globular clusters has been performed, but their gamma-ray pulsation emissions or flux variabilities are not found. The numbers of millisecond pulsars (MSPs) in these globular clusters are estimated under the assumption that each MSP inside globular clusters emits a similar amount of gamma-rays. Some possible origins of gamma-ray emission from globular clusters, such as MSPs, pulsar binary systems and/or dark matter, are discussed.