Keck page on the discovery:
http://www2.keck.hawaii.edu/optics/staff/mvandam/gabrielle
Xena and its moon
Gabrielle, a moon of Xena, was discovered on September 10, 2005. The discovery was made using the Laser Guide Star Adaptive Optics (LGS AO) system at the W.M. Keck Observatory. Images were taken at infrared wavelengths (2.1 microns) using the NIRC2 imaging camera over a period of 40 minutes. Gabrielle is located to the right of Xena in the picture.

The scale is in arcseconds...
