VERITAS Observations of Globular Clusters

McCutcheon, Michael
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It has been postulated that globular clusters could be sources of Very-High Energy (VHE) gamma rays, powered by milli-second pulsars. This could be due to cumulative direct emission or to plerion-type emission driven by colliding winds. In particular the southern hemisphere globular cluster 47 Tuc has been singled out as a potential source in both models. In light of the recent detection by the Fermi Gamma-ray Space Telescope (FGST) of 47 Tuc, the first detection of any globular cluster as a gamma-ray source, we present the results of observations of northern hemisphere globular clusters by VERITAS. Three globular clusters have been observed: M15, M13 and M5. Of these, M15 and M13 have been explicitly proposed as VHE gamma-ray sources and M5 possess similarities with them.
Comment: 3 pages, no figures, to be published in Proceedings of the 31st International Cosmic Ray Conference (ICRC), Lodz, Poland, July 2009 except an error in the conversion of the upper limits corrected here
Astrophysics - High Energy Astrophysical Phenomena