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We study the gamma-ray spectra of 30 globular clusters (GCs) thus fardetected with the Fermi Gamma-ray Space Telescope. Presuming that gamma-rayemission of a GC comes from millisecond pulsars (MSPs) contained in, a modelthat generates spectra for the GCs is built based on the gamma-ray propertiesof the detected MSP sample. We fit the GCs' spectra with the model, and for 27of them, their emission can be explained with arising from MSPs. The spectra ofthe other three, NGC 7078, 2MS-GC01, and Terzan 1, can not be fit with ourmodel, indicating that MSPs' emission should not be the dominant one in thefirst two and the third one has a unique hard spectrum. We also investigate sixnearby GCs that have relatively high encounter rates as the comparison cases.The candidate spectrum of NGC 6656 can be fit with that of one MSP, supportingits possible association with the gamma-ray source at its position. The fiveothers do not have detectable gamma-ray emission. Their spectral upper limitsset limits of $\leq 1$ MSPs in them, consistent with the numbers of radio MSPsfound in them. The estimated numbers of MSPs in the gamma-ray GCs generallymatch well those reported for radio pulsars. Our studies of the gamma-ray GCsand the comparison nearby GCs indicate that the encounter rate should not bethe only factor determining the number of MSPs a GC contains.

Gamma-ray spectral properties of the Galactic globular clusters: constraint on the numbers of millisecond pulsars