# VERITAS Observations of Globular Clusters

## TL;DR

This paper reports VERITAS observations of northern hemisphere globular clusters M15, M13, and M5, exploring their potential as sources of very-high-energy gamma rays, inspired by recent Fermi detections of similar clusters.

## Contribution

It presents the first VHE gamma-ray observations of northern globular clusters, expanding the search beyond previously studied southern clusters like 47 Tuc.

## Key findings

- No significant VHE gamma-ray emission detected from M15, M13, or M5.
- Supports the need for further observations to confirm potential gamma-ray sources.
- Provides upper limits on gamma-ray fluxes from these clusters.

## Abstract

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.