Ionized Ultraviolet and Soft-X-ray Absorption in the Low Redshift Active Galactic Nucleus PG1126−041

We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray weak, far-infrared loud AGN, PG 1126−041 (Mrk 1298). The first UV spectra taken in June 1992, simultaneously with ROSAT, show strong absorption lines of NV, CIV and SiIV, extending over a velocity range from −1000 to −5000 km s 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 Jan. 1995, the continuum was a factor of two brighter and the UV absorption lines are found to be considerably weaker than in 1992, but only little variation in the emission line fluxes is found. With UV spectral indices of αuv ≃ 1.82 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 due to 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 αuvx = 2.32. Highly ionized (warm) absorption is suggested by the ROSAT data. After correcting for a warm absorber, the optical to X-ray spectral slope is close to the average of αuvx ≃ 1.67 for radio quiet quasars. From photoionization calculations we find: (1) A single zone absorption model cannot explain simultaneously the UV absorption lines and the ionized X-ray absorption if metal abundances are solar. Furthermore, in order to be consistent with the equivalent width of the observed Lyα absorption line, the turbulent velocity of the warm absorber must be less than 190 km s, which imposes serious constraints on a disk wind model. (2) The UV absorption lines and their variability cannot be explained by a single zone model with solar abundances and the large variability in the absorption lines suggest that CIV and NV absorption lines are not severely saturated. (3) The absorption of the ionizing continuum by warm material strongly affects the emission line spectrum.