Abramowski, A., Acero, F., Aharonian, F., Akhperjanian, A., Anton, G., Balzer, A., …Collaboration, H. (2011). H.E.S.S. Observations of the Globular Clusters NGC 6388 and M15 and Search for a Dark Matter Signal. Astrophysical Journal, 735, https://doi.org/10.1088/0004-637x/735/1/12