Globular clusters (GCs) are the  oldest and most dense stellar systems in the Galaxy. The dynamical  interactions with high stellar encounter rate are expected to form  low-mass X-ray binaries (LMXBs). Millisecond pulsars (MSPs) are  generally believed to be the descendants of LMXBs. It is also widely  accepted that MSPs contribute almost all gamma ray emissions of GCs.  There is already 9 GCs have been associated with gamma ray emitters. By  analysing more than 6 years survey data of Fermi-LAT, we confirm the  significant gamma ray emission from 2MS-GC01 and IC 1257, and report the  discovery for gamma ray emission from NGC 5904 and NGC 6656 within  their tidal radii. An strong evidence of significant gamma ray emission  is found from FSR 1735. 

   Figure 1.   TS maps of the ROIs for NGC 5904,  NGC 6656 and FSR 1735. The cross represents the best-fitting centroid of  their γ-ray emission. Thecircles represent the tidal radii (Harris  1996, 2003 version). The tidal radius of FSR 1735 is unknown.

  The above figures represent TS  maps of ROI (region of interest) from NGC 5904 and NGC 6656. The cross  represent the best-fit centriod of the  gamma  ray emission from them, while the circle for the tidal radius. We  estimate the population of MSPs in each GC, which is larger than the  number of  known. It may be limited by the sensitivity of existing radio  telescopes. This work is done by Jianeng Zhou of Purple Mountain  Observatory who is collaborated with Pengfei Zhang, Xiaoyuan Huang,  Xiang Li, Yunfeng Liang, Lei Fu, Jingzhi Yan and Qingzhong Liu, which is  accepted by MNRAS and available at http://mnras.oxfordjournals.org/content/448/4/3215.full.pdf