We re-examine the X-ray luminosity-temperature relation using a nearly
homogeneous data set of 24 clusters selected for statistically accurate
temperature measurements and absence of strong cooling flows. The data exhibit
a remarkably tight power-law relation between bolometric luminosity and
temperature with a slope 2.88 \pm 0.15. With reasonable assumptions regarding
cluster structure, we infer an upper limit on fractional variations in the
intracluster gas fraction <(\delta\fgas/\fgas)^2)^1/2 \le 15%. Imaging data
from the literature are employed to determine absolute values of fgas within
spheres encompassing density contrast 500 and 200 with respect to the critical
density. Comparing binding mass estimates based on the virial theorem (VT) and
the hydrostatic, betamodel (BM), we find a temperature-dependent discrepancy in
fgas between the two methods caused by sytematic variation of the outer slope
parameter beta with temperature. There is evidence that cool clusters have a
lower mean gas fraction that hot clusters, but it is not possible to assess the
statistical significance of this effect in the present dataset. The temperature
dependance of the ICM density structure, coupled with the increase of the gas
fraction with T in the VT aproach, explains the steepening of the Lx-T
relation. The small variation about the mean gas fraction within this majority
sub-population of clusters presents an important constraint for theories of
galaxy formation and supports arguments against an Einstein-deSitter universe
based on the population mean gas fraction and primordial nucleosynthesis. The
apparent trend of lower gas fractions and more extended atmospheres in low T
systems are consistent with expectations of models incorporating the effects of
galactic winds on the ICM. ABRIDGEDComment: 11 pages, 4 figures, uses mn.sty and epsf.sty, accepted for
publication in MNRAS; minor modifications: discussion added on CF LX (Sec.
3.1);comparison with Allen & Fabian L-T results (Sec.3.1 & Sec.4.4);
statistics precised (3.1), discussion clarified (Sec. 2.2,Sec. 4.4); slight
mistake in the r-T and M-T relation calibration corrected and thus fgas in
Fig.3, Fig 4, Tab 2 slightly change
