X-ray observations of the interacting system Arp 284
  We discuss the X-ray properties of the interacting system Arp 284, consisting of the active nuclear starburst galaxy NGC 7714 and its post-starburst companion NGC 7715. A morphological signature of the interaction, thought to have started <100 Myr ago, is an asymmetric stellar ring dominating the intensity profile of NGC 7714 in the inner disk (~ 2 exponential scale lengths). In agreement to previous Einstein-data our ROSAT PSPC exposure shows the X-ray emission of Arp 284 to be confined to NGC 7714. The bulk of the intrinsic X-ray luminosity in the ROSAT 0.1--2.4 keV band can be accounted for by thermal emission from hot (~5x10**6 K) gas and amounts to ~2-4 x 10**41 erg/sec. Follow-up observations with the ROSAT HRI revealed two distinct extended emitting regions contributing to the X-ray luminosity in NGC 7714. The more luminous of them (L_X < 2 x 10*41 erg/sec) coincides with the central starburst nucleus and can be explained this way. The fainter one (L_X~ 8x10**40 erg/sec) is located ~20 arcsec off-center and does not have any conspicuous optical counterpart. It is, likely, located at the borderline between the stellar ring and a massive (>10**9 M(solar)) HI-bridge further to the east possibly intersecting NGC 7714. The HI and X-ray morphology and the extensive starburst nature of the nuclear energy source suggest different scenarios for the formation of the eastern emission spot. The possibilities of (i) collisional heating of the outlying gas by a starburst-driven nuclear wind and (ii) infall of HI-clouds from the bridge onto the disk of NGC 7714 are discussed. 
P. Papaderos, K.J. Fricke (Universitaets-Sternwarte Goettingen)