Ionized ultraviolet and soft X-ray absorption in the low-redshift active galactic nucleus PG 1126-041

We present here the analysis of ultraviolet spectra from IUE and an X-ray s pectrum from ROSAT PSPC observations of the X-ray-weak, far-infrared-loud A GN, PC 1126-041 (Mrk 1298). The first UV spectra taken in 1992 June, simult aneously with ROSAT, show strong absorption lines of N V, C IV and Si IV, e xtending over a velocity range from -1000 to -5000 km s(-1) with respect to the corresponding line centre. Our analysis shows that the broad emission- line region (BELR) is, at least partially, covered by the material causing these absorption lines. In the IUE spectrum taken in 1995 January, the cont inuum was a factor of 2 brighter and the UV absorption lines are found to b e considerably weaker than in 1992, but little variation in the emission-li ne fluxes is found. With UV spectral indices of auv similar or equal to 1.8 2 and 1.46 for the 1992 and 1995 data, the far-UV spectrum is steep. Based on the emission-line ratios and the broad-band spectral energy distribution , we argue that the steepness of the UV spectrum is unlikely to be caused b y reddening. The soft X-ray emission in the ROSAT band is weak. A simple power-law model yields a very poor fit with a UV-to-X-ray spectral index alpha(UVX) = 2.3. Highly ionized (warm) absorption is suggested by the ROSAT data. After cor recting for a warm absorber, the optical to X-ray spectral slope is close t o the average of alpha(UVX) similar or equal to 1.67 for radio-quiet quasar s. From photoionization calculations we find the following results. (1) A sing le-zone absorption model cannot explain simultaneously the UV absorption li nes and the ionized X-ray absorption if metal abundances are solar. Further more, in order to be consistent with the equivalent width of the observed L y alpha absorption line, the turbulent velocity of the warm absorber must b e less than 190 km s(-1), which imposes serious constraints on a disc wind model. (2) The UV absorption lines and their variability cannot be explaine d by a single-zone model with solar abundances and the large variability in the absorption lines suggests that C IV and N V absorption lines are not s everely saturated. (3) The absorption of the ionizing continuum by warm mat erial strongly affects the emission-line spectrum.