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We present the first results on the hard X-ray continuum image (up to 15 keV)of the supernova remnant Cas A measured with the EPIC cameras onboardXMM-Newton. The data indicate that the hard X-ray tail, observed previously,that extends to energies above 100 keV does not originate in localised regions,like the bright X-ray knots and filaments or the primary blast wave, but isspread over the whole remnant with a rather flat hardness ratio of the 8-10 and10-15 keV energy bands. This result does not support an interpretation of thehard X-radiation as synchrotron emission produced in the primary shock, inwhich case a limb brightened shell of hard X-ray emission close to the primaryshock front is expected. In fact a weak rim of emission near the primary shockfront is discernable in the hardest X-ray image but it contains only a fewpercent of the hard X-ray emissivity. The equivalent width of the Fe-K lineblend varies by more than an order of magnitude over the remnant, it is hard toexplain this as Fe-emission from the reverse shock heated ejecta given theejecta temperature and the age of the remnant. The uniquely highwavelength-dispersive RGS-spectrometer has allowed, for the first time, toextract monochromatic images in several highly ionised element species withhigh spectral resolution. We present here a preliminary result on themeasurement of the O VIII Ly-alpha and Ly-beta brightness distribution andbrightness ratios. The large observed decrease of the Ly-alpha/Ly-beta ratiogoing from the N to the SE can be explained by small-scale (10 arcsec)variations in the N_H column over the remnant and the potential presence ofresonance scattering of the O VIII Ly-alpha photons in the limb brightenedshell.Comment: 5 pages, 6 figures. accepted for publication in Astronomy and  Astrophysics, letters (XMM issue

Cassiopeia A: On the origin of the hard X-ray continuum and the implication of the observed O vııı Ly-α/Ly-β distribution