1999A&A...348..711N

We used archival ROSAT observations to investigate the X-ray surface brightness profiles of a sample of 26 clusters in the redshift range 0.04<z<0.06. For 15 of these clusters accurate temperatures (kT_X > 3.5keV) were available from the literature. The scaled emission measure profiles look remarkably similar above ∼0.2 times the virial radius (r_VT200). On the other hand a large scatter is observed in the cluster core properties. We fitted a β-model (with and without excising the central part) to all the ROSAT profiles to quantify the structural variations in the cluster population, unraveling a robust quadratic correlation between the core radius and the slope parameter β. We quantified the shape of each gas density profile by the variation with radius of the logarithmic slope, α_n. The bi-weight dispersion of α_n among the clusters is less than 20% for any given scaled radii above x=0.2. There is a clear minimum spread at x=0.3, which is related to the existence of a correlation between core radius and β. These ensemble properties are insensitive to the exact treatment of a possible central excess when fitting the profiles. On the other hand the scatter in αn is decreased when the radii are scaled to r_VT200. The regularity we found in the gas profiles at x>0.2 supports the existence of a universal underlying dark matter profile, as already predicted by theoretical works. It suggests that non gravitational heating is negligible for clusters with temperature above ∼3.5keV. Our results are consistent with the classical scaling relation between Mass and Temperature (M∝T^3/2(1+z)^–3/2). Accordingly the spread in the scaled mass profiles derived from the hydrostatic isothermal β-model is small. The very large scatter observed in the core properties favor scenario where Cooling Flows are periodically erased by merger events.