We report the discovery of XMMXCS J2215.9-1738 , a massive galaxy cluster at z = 1.45 , which was found in the XMM Cluster Survey .
The cluster candidate was initially identified as an extended X-ray source in archival XMM data .
Optical spectroscopy shows that 6 galaxies within a \sim 60 arcsec diameter region lie at z = 1.45 \pm 0.01 .
Model fits to the X-ray spectra of the extended emission yield kT = 7.4 ^ { +2.7 } _ { -1.8 } keV ( 90 % confidence ) ; if there is an undetected central X-ray point source then kT = 6.5 ^ { +2.6 } _ { -1.8 } keV .
The bolometric X-ray luminosity is L _ { x } = 4.4 ^ { +0.8 } _ { -0.6 } \times 10 ^ { 44 } ergs s ^ { -1 } over a 2 Mpc radial region .
The measured T _ { x } , which is the highest known for a cluster at z > 1 , suggests that this cluster is relatively massive for such a high redshift .
The redshift of XMMXCS J2215.9-1738 is the highest currently known for a spectroscopically-confirmed cluster of galaxies .