The Mass of Abell 1060 and AWM 7 from Spatially Resolved X-ray   Spectroscopy: Variations in Baryon Fraction
  Using X-ray temperature and surface brightness profiles of the hot intracluster medium derived from ASCA and ROSAT observations we place constraints on the dark matter and baryon fraction distributions in the poor clusters Abell 1060 and AWM 7. Although their total mass distributions are similar, AWM 7 has twice the baryon fraction of Abell 1060 in the best-fit models. The functional form of the dark matter distribution is ill-determined, however mass models where the baryon fractions in Abell 1060 and AWM 7 significantly overlap are excluded. Such variations in baryon fraction are not predicted by standard models and imply that some mechanism in addition to gravity plays a major role in organizing matter on cluster scales. 
Michael Loewenstein and Richard Mushotzky (NASA/GSFC)