IS MS 1054-03 an exceptional cluster? A new investigation of ROSAT HRI X-ray data

We reanalyzed the ROSAT HRI observation of MS 1054-03, optimizing the chann el HRI selection and including a new exposure of 68 ks. From a wavelet anal ysis of the HRI image we identify the main cluster component and find evide nce for substructure in the west, which might be either a group of galaxies falling onto the cluster or a foreground source. Our one- and two-dimensio nal analysis of the data show that the cluster can be fitted well by a clas sical beta model centered only 20 " away from the central cD galaxy. The co re radius and beta values derived from the spherical model (beta = 0.96(-0. 22)(+0.48)) and the elliptical model (beta = 0.73 +/- 0.18) are consistent. We derived the gas mass and total mass of the cluster from the beta -model fit and the previously published ASCA temperature (12.3(-2.2)(+3.1) keV). The gas mass fraction at the virial radius is f(gas) = (14[-3, + 2.5] +/- 3 )% for Omega (0) = 1, where the errors in square brackets come from the unc ertainty on the temperature, and the remaining errors from the HRI imaging data. The gas mass fraction computed for the best-fit ASCA temperature is s ignificantly lower than found for nearby hot clusters, f(gas) = (20.1 + 1.6 )%. This local value can be matched if the actual virial temperature of MS 1054-03 were close to the lower ASCA limit (similar to 10 keV), with an eve n lower value of 8 keV giving the best agreement. Such a bias between the v irial and measured temperature could be due to the presence of shock waves in the intracluster medium, stemming from recent mergers. Another possibili ty, which reconciles a high temperature with the local gas mass fraction, i s the existence of a nonzero cosmological constant.