X
- XBS — XMM-Newton, Bright Source
- XBSS — XMM-Newton Bright Serendipitous Survey
- XEST — XMM-Newton Extended Survey of the Taurus Molecular
- XEST-OM — XEST, Optical/UV Monitor
- XTE — X-ray Timing Explorer
Read more about this topic: List Of Astronomical Catalogues