Hopwood, M. E. L.; Evans, A.; Roberts, T. P.; Burleigh, M. R.; Odenkirchen, M.; Beardmore, A. P.; O'brien, T.; Jeffries, R. D.; et al. (juli 2000). ”A possible detection of diffuse extended X-ray emission in the environment of the globular cluster NGC 6779”. Monthly Notices of the Royal Astronomical Society 316 (1): sid. L5–L8. doi:10.1046/j.1365-8711.2000.03717.x.