No abstract

Zwicky 159.034, one of the Seyfert galaxies identi ed with EUV sources detected during the ROSAT Wide Field Camera (WFC) all-sky survey, has unusual properties. The ROSAT Position Sensitive Proportional Counter (PSPC) 0.1{2.5 keV X-ray spectrum, obtained simultaneously with the WFC survey, appears extremely steep.Subsequent deeper pointed observations with ROSAT revealed that its 0.1{2.5 keV count rate had decreased by an extremely large amount (a factor of 70). This is comparable to the variability amplitude seen in another ultrasoft Seyfert, E1615+061. There appears to be 10 times as much ux in the soft component as in any expected hard tail suggesting that, in the absence of partial covering of the hard ux, the soft ux cannot arise via reprocessing of the hard tail. Its peculiar optical spectrum has permitted lines with widths 1 200{1 500 km s 1 , and forbidden lines are weak or absent. Its optical spectrum shows evidence for variability, and might be used to study the role reprocessed X-rays play in the formation of optical lines.

We report evidence for persistent giant and rapid X-ray variability in the radio-quiet, ultrasoft, strong Fe ii, narrow-line Seyfert 1 galaxy IRAS 13224-3809. Within a 30 day ROSAT High Resolution Imager (HRI) monitoring observation at least five giant amplitude count rate variations are visible, with the maximum observed amplitude of variability being about a factor of 60. We detect a rise by a factor of about 57 in just two days. IRAS 13224-3809 appears to be the most X-ray variable Seyfert known, and its variability is probably nonlinear. We carefully check the identification of the highly variable X-ray source with the distant galaxy, and it appears to be secure. We examine possible explanations for the giant variability. Unusually strong relativistic effects and partial covering by occulting structures on an accretion disc can provide plausible explanations of the X-ray data, and we explore these two scenarios. Relativistic boosting effects may be relevant to understanding the strong X-ray variability of some steep spectrum Seyferts more generally.

The 120 000 X-ray sources detected in the RASS II processing of the ROSAT All-Sky Survey are correlated with the 14 315 IRAS galaxies selected from the IRAS Point Source Catalogue: 372 IRAS galaxies show X-ray emission within a distance of 100 arcsec from the infrared position. By inspecting the structure of the X-ray emission in overlays on optical images we quantify the likelihood that the X-rays originate from the IRAS galaxy. For 197 objects the soft X-ray emission is very likely associated with the IRAS galaxy. Their soft X-ray properties are determined and compared with their farinfrared emission. X-ray contour plots overlaid on Palomar Digitized Sky Survey images are given for each of the 372 potential identifications. All images and tables displayed here are also available in electronic form.