N ov 1 99 7 To appear in ApJ , part 1 The Lensing Cluster MS 0440 + 0204 Seen by HST , ROSAT and ASCA : I . Cluster Properties

We present an analysis of the properties of the lensing cluster MS0440+0204 at z=0.1965. MS0440+0204 has been observed with a variety of telescopes at diverse wavelengths: from the ground with CFHT, MMT and KECK and from Earth orbit with HST, ROSAT and ASCA. Mass determinations are separately obtained from galaxy virial motions and X-ray profile fitting. A simple β-model fit to the X-ray data yields a mass of (1.3±0.2) × 10M⊙ within 583 kpc of the cluster center, but more general models fit all of our data better and allow a wider range of masses that are consistent with the lensing data. In addition, the X-ray data yield a mass distribution profile that is well described by a β model with a core radius of 26.7 kpc. The velocity dispersion of galaxies yields a mass of 4.8 −0.94 × 10M⊙ within 900 kpc. In the inner 24. 5 there are 24 arcs that appear to be strong gravitationally lensed images of background sources. Models of the cluster mass distribution and its lensing properties reveal 5 background sources at various redshifts each forming 2 or more arcs. We do not have a redshift for any arc with multiple images, therefore we can only place upper and lower limits to the mass of the cluster from gravitational lensing. At 100 kpc, the lower limit mass from lensing is about a factor of 2 greater than the X-ray determined mass. The rate of increase in the projected mass at this radius also is greater for the Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS5-26555, as well as on observations made with the Multiple Mirror Telescope Observatory, which is operated jointly by the University of Arizona and the Smithsonian Institution Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822 Istituto di Radioastronomia del CNR, Via Gobetti 101, I-40129, Bologna, ITALY Visiting Astronomer at CFHT, operated by the National Research Council of Canada, le Centre National de la Recherche Scientifique de France and the University of Hawai′i , and at the W. M. Keck Observatory, jointly operated by the California Institute of Technology and the University of California Physics Department, University of Maryland, College Park, MD 20742 DAEC, Observatoire de Paris Meudon, 92195 Meudon Principal Cedex, FRANCE Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138