BeppoSAX observations of two high redshift clusters of galaxies: RXJ 0152.7 1357 and MS 2053.7 0449

We present X-ray observations of two high redshift clusters of galaxies carried out with the BeppoSAX satellite. One cluster, RXJ 0152.7 1357 at z ' 0:83, was selected from the ROSAT Deep Cluster Survey sample, as one of the most X-ray luminous systems known at z> 0:5. The optical and ROSAT-PSPC data show a complex morphology with at least two cores. Our SAX observations yield a gas temperature kT =6 :46 +1:74 1:19 keV and a metallicity A =0 :53 +0:29 0:24, with a prominent iron K line. The second cluster, MS 2053.7 0449 at z ' 0:58, was selected from the EMSS sample. Given the poor statistics no constraints on the metallicity can be derived from the present data. Large uncertainties are associated to the gas temperature (kT =6 :7 +6:8 2:3 keV), which has been obtained after fixing the abundance to 0.3 solar. Combining these results with those obtained for similarly high redshift (z 0:5) clus- ters of galaxies with broad band X-ray spectra, we discuss the high redshift Lbol T relationship. The data can easily be ac- commodated with a non-evolving (or mildly evolving) Lbol T relation, a result which, when combined with the little observed evolution in the bulk of the X-ray cluster population, gives sup- port to low cosmological models.