We present a measurement of the cluster X-ray luminosity-temperature relation out to high redshift ( z \sim 0.8 ) .
Combined ROSAT PSPC spectra of 91 galaxy clusters detected in the Wide Angle ROSAT Pointed Survey ( WARPS ) are simultaneously fit in redshift and luminosity bins .
The resulting temperature and luminosity measurements of these bins , which occupy a region of the high redshift L-T relation not previously sampled , are compared to existing measurements at low redshift in order to constrain the evolution of the L-T relation .
We find a best fit to low redshift ( z < 0.2 ) cluster data , at T > 1 keV , to be L \propto T ^ { 3.15 \pm 0.06 } .
Our data are consistent with no evolution in the normalisation of the L-T relation up to z \sim 0.8 .
Combining our results with ASCA measurements taken from the literature , we find \eta = 0.19 \pm 0.38 ( for \Omega _ { 0 } = 1 , with 1 \sigma errors ) where L _ { Bol } \propto { ( 1 + \it z ) } ^ { \eta } T ^ { 3.15 } , or \eta = 0.60 \pm 0.38 for \Omega _ { 0 } = 0.3 .
This lack of evolution is considered in terms of the entropy-driven evolution of clusters .
Further implications for cosmological constraints are also discussed .