via the archive. For the data preparation, they follow closely the method outlined in @Maughan2008. The *Chandra* analysis package used was CIAO[^1] version 4.2 and calibration database CALDB 4.1.4. As in @Maughan2008, blank sky, rather than local, backgrounds are used because the clusters fill a large fraction of the field of view.

We fit a gas density model by converting the observed surface brightness profile into a projected emissivity profile, which was then modelled by projecting the modifed $\beta$–model of [@Vikhlinin2006] along the line of sight (see [@Maughan2008] for details). Gas parameters and errors were determined from Monte Carlo realisations of the projected emissivity profile. At each data point a new randomised point was drawn from a Gaussian distribution centered on the model value at that point, with a standard deviation equal to the fractional measurement error on the original data point, multiplied by the model value. The error bar on this new randomised point was set to the same fractional size as the error bar on the original observed point.

The cluster temperature, gas mass and $R_{500}$ (the radius enclosing a mean density of 500 times the critical density at the cluster’s redshift) were then determined iteratively. The procedure 