Context :

Aims : Power-law cosmologies , in which the cosmological scale factor evolves as a power law in the age , a \propto t ^ { \alpha } with \alpha \ga 1 , regardless of the matter content or cosmological epoch , is comfortably concordant with a host of cosmological observations .

Methods : In this article , we use recent measurements of the X-ray gas mass fractions in clusters of galaxies to constrain the \alpha parameter with curvature k = \pm 1 , 0 .

Results : We find that the best fit happens for an open scenario with the power index \alpha = 1.14 \pm 0.05 , though the flat and closed model can not be rule out at very high confidence level .

Conclusions : Our results are in agreement with other recent analyses and show that the X-ray gas mass fraction measurements in clusters of galaxies provide a complementary test to the power law cosmology .