Is MS 1054−03 an Exceptional Cluster? A New Investigation ofROSATHRI X‐Ray Data

We reanalyzed the ROSAT HRI observation of MS 1054[03, optimizing the channel HRI selection and including a new exposure of 68 ks.From a wavelet analysis of the HRI image we identify the main cluster component and Ðnd evidence 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-dimensional analysis of the data show that the cluster can be Ðtted well by a classical b model centered only 20A away from the central cD galaxy.The core radius and b values derived from the spherical model and the ellip-(b \ 0.96 ~0.22 `0.48) tical model (b \ 0.73 ^0.18) are consistent.We derived the gas mass and total mass of the cluster from the b-model Ðt and the previously published ASCA temperature keV).The gas mass fraction at (12.3 ~2.2 `3.1 the virial radius is for where the errors in square brackets come f gas \ (14[[3, ] 2.5] ^3)% ) 0 \ 1, from the uncertainty on the temperature, and the remaining errors from the HRI imaging data.The gas mass fraction computed for the best-Ðt ASCA temperature is signiÐcantly lower than found for nearby hot clusters, This local value can be matched if the actual virial temperature of MS f gas \ (20.1 ^1.6)%.1054[03 were close to the lower ASCA limit (D10 keV), with an even lower value of 8 keV giving the best agreement.Such a bias between the virial and measured temperature could be due to the presence of shock waves in the intracluster medium, stemming from recent mergers.Another possibility, which reconciles a high temperature with the local gas mass fraction, is the existence of a nonzero cosmological constant.