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Hopwood, M. E. L.; et al. (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): L5–L8, Bibcode:2000MNRAS.316L...5H, doi:10.1046/j.1365-8711.2000.03717.xParameter |month= yang tidak diketahui akan diabaikan (bantuan)