A detailed X-ray analysis of an XMM-Newton observation of the high-redshift ( z=0.89 ) galaxy cluster ClJ1226.9 + 3332 is presented .
After careful consideration of background subtraction issues , the X-ray temperature is found to be 11.5 ^ { +1.1 } _ { -0.9 } \mbox { $ \mathrm { ~ { } keV } $ } , the highest X-ray temperature of any cluster at z > 0.6 .
The temperature is consistent with the observed velocity dispersion .
In contrast to MS1054-0321 , the only other very hot cluster currently known at z > 0.8 , ClJ1226.9 + 3332 features a relaxed X-ray morphology , and its high overall gas temperature is not caused by one or several hot spots .
The system thus constitutes a unique example of a high redshift ( z > 0.8 ) , high temperature ( T > 10 keV ) , relaxed cluster , for which the usual hydrostatic equilibrium assumption , and the X-ray mass is most reliable .

A temperature profile is constructed ( for the first time at this redshift ) and is consistent with the cluster being isothermal out to 45 \% of the virial radius .
Within the virial radius ( corresponding to a measured overdensity of a factor of 200 ) , a total mass of 1.4 \pm 0.5 \times 10 ^ { 15 } M _ { \odot } is derived , with a gas mass fraction of 12 \pm 5 \% ( for a \Lambda CDM cosmology and H _ { 0 } =70 km s ^ { -1 } Mpc ^ { -1 } ) .
This total mass is similar to that of the Coma cluster .
The bolometric X-ray luminosity is 5.3 ^ { +0.2 } _ { -0.2 } \times 10 ^ { 45 } \mathrm { \mbox { $ \mathrm { ~ { } erg } $ } \mathrm { \mbox { $% \mathrm { ~ { } s } $ } ^ { -1 } } } .
Analysis of a short Chandra 
observation confirms the lack of significant point-source contamination , the temperature , and the luminosity , albeit with lower precision .
The probabilities of finding a cluster of this mass within the volume of the discovery X-ray survey are \sim 8 \times 10 ^ { -5 } 
for \Omega _ { M } = 1 and 0.64 for \Omega _ { M } = 0.3 , making \Omega _ { M } = 1 highly unlikely .

The entropy profile suggests that entropy evolution is being observed .
The metal abundance ( of Z = 0.33 ^ { +0.14 } _ { -0.10 } \mathrm { Z _ { \odot } } ) , gas mass fraction , and gas distribution are consistent with those of local clusters ; thus the bulk of the metals were in place by z=0.89 .