to fit regions of the cluster within $r_{2500}$, the radius at which the mean enclosed density is 2500 times the universal critical density at the redshift of the cluster. At relatively small radii the isothermal $\beta$ model is found to be accurate in reproducing the average observable and physical properties of many clusters [see e.g. @Grego:2000; @Reese:2002; @LaRoque:2006]. However, deep X-ray spectral observations of nearby cluster samples using *Chandra* [see e.g. @Vikhlinin:2006] and *XMM-Newton* [see e.g. @Pratt:2007] show that at larger radii the ICM temperature declines with radius. Hence for low-resolution pointed SZ observations that are sensitive to the outskirts of the cluster gas, there is a clear requirement for a more physically motivated non-isothermal model that is simple enough to be constrained by the data.

There have been a number of recent approaches amongst SZ and X-ray observers to relax the assumption of isothermality in clusters and model the ICM in a physical way. For *Chandra* observations of nearby relaxed clusters, [@Vikhlinin:2006] developed a modified $\beta$ model of the electron density to fit the observed cores and steeper outer profiles of relaxed clusters. In that work the temperature is parameterized by a broken power law at large radii and 