Discovery of the Central Excess Brightness in Hard X‐Rays in the Cluster of Galaxies Abell 1795

Using the X-ray data from \ASCA, spectral and spatial properties of theintra-cluster medium (ICM) of the cD cluster Abell 1795 are studied, up to aradial distance of $\sim 12'$ ($\sim 1.3$ $h_{50}^{-1}$ kpc). The ICMtemperature and abundance are spatially rather constant, although the coolemission component is reconfirmed in the central region. The azimuthally-averaged radial X-ray surface brightness profiles are very similar between soft(0.7--3 keV) and hard (3--10 keV) energy bands, and neither can be fitted witha single-$\beta$ model due to a strong data excess within $\sim5'$ of thecluster center. In contrast, double-$\beta$ models can successfully reproducethe overall brightness profiles both in the soft and hard energy bands, as wellas that derived with the \ROSAT PSPC. Properties of the central excessbrightness are very similar over the 0.2--10 keV energy range spanned by \ROSATand \ASCA. Thus, the excess X-ray emission from the core region of this clusteris confirmed for the first time in hard X-rays above 3 keV. This indicates thatthe shape of the gravitational potential becomes deeper than the King-type onetowards the cluster center. Radial profiles of the total gravitating matter,calculated using the double-$\beta$ model, reveal an excess mass of $\sim 3\times 10^{13}~ M_{\odot}$ within $\sim 150 h^{-1}_{50}$ kpc of the clustercenter. This suggests a hierarchy in the gravitational potential correspondingto the cD galaxy and the entire cluster.Comment: 27 pages, 8 figures; to appear ApJ 500 (June 20, 1998