Heavy X-ray Absorption in Soft X-ray Weak Active Galactic Nuclei

Recent ROSAT studies have identified a significant population of Active Galactic Nuclei (AGN) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGN intrinsically X-ray weak or are they just highly absorbed? Brandt, Laor & Wills have systematically examined the optical and UV spectral properties of a well-defined sample of these soft X-ray weak (SXW) AGN drawn from the Boroson & Green sample of all the Palomar Green AGN with z < 0.5. We present ASCA observations of three of these SXW AGN: PG 1011–040, PG 1535+547 (Mrk 486), and PG 2112+059. In general, our ASCA observations support the intrinsic absorption scenario for explaining soft X-ray weakness; both PG 1535+547 and PG 2112+059 show significant column densities (NH ≈ 10–10 cm) of absorbing gas. Interestingly, PG 1011–040 shows no spectral evidence for X-ray absorption. The weak X-ray emission may result from very strong absorption of a partially covered source, or this AGN may be intrinsically X-ray weak. PG 2112+059 is a Broad Absorption Line (BAL) QSO, and we find it to have the highest X-ray flux known of this class. It shows a typical power-law X-ray continuum above 3 keV; this is the first direct evidence that BAL QSOs indeed have normal X-ray continua underlying their intrinsic absorption. Finally, marked variability between the ROSAT and Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA Physics Department, Technion, Haifa 32000, Israel Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210-1106, USA Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA The Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan