P. H. T. Tam, A. K. H. Kong, C. Y. Hui, K. S. Cheng, C. Li, T.-N. Lu. Gamma-ray emission from the globular clusters Liller 1, M80, Ngc 6139, Ngc 6541, Ngc 6624, and Ngc 6752
Natural Sciences / Astronomy / Astrophysics
Submitted on: Sep 11, 2012, 16:29:36
Description: Globular clusters (GCs) are emerging as a new class of gamma-ray emitters, thanks to the data obtained from the Fermi Gamma-ray Space Telescope. By now, eight GCs are known to emit gamma-rays at energies >100~MeV. Based on the stellar encounter rate of the GCs, we identify potential gamma-ray emitting GCs out of all known GCs that have not been studied in details before. In this paper, we report the discovery of a number of new gamma-ray GCs: Liller 1, NGC 6624, and NGC 6752, and evidence for gamma-ray emission from M80, NGC 6139, and NGC 6541, in which gamma-rays were found within the GC tidal radius. With one of the highest metallicity among all GCs in the Milky Way, the gamma-ray luminosity of Liller 1 is found to be the highest of all known gamma-ray GCs. In addition, we confirm a previous report of significant gamma-ray emitting region next to NGC 6441. We briefly discuss the observed offset of gamma-rays from some GC cores.