Open AccessIonized ultraviolet and soft X‐ray absorption in the low‐redshift active galactic nucleus PG 1126−041
Author(s) -
Wang T. G.,
Brinkmann W.,
Wamsteker W.,
Yuan W.,
Wang J. X.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02650.x
Subject(s) - rosat , physics , astrophysics , redshift , spectral line , emission spectrum , quasar , ultraviolet , absorption spectroscopy , active galactic nucleus , absorption (acoustics) , line (geometry) , ionization , spectral index , spectral slope , astronomy , galaxy , optics , ion , geometry , mathematics , quantum mechanics
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 1992 June, simultaneously with ROSAT , show strong absorption lines of N v , C iv and Si iv , extending 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 continuum was a factor of 2 brighter and the UV absorption lines are found to be considerably weaker than in 1992, but little variation in the emission‐line fluxes is found. With UV spectral indices of α UV ≃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 caused by 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 α UVX =2.3. 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 α UVX ≃1.67 for radio‐quiet quasars. From photoionization calculations we find the following results. (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 Ly α absorption line, the turbulent velocity of the warm absorber must be 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 explained 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 severely saturated. (3) The absorption of the ionizing continuum by warm material strongly affects the emission‐line spectrum.