ASCA Observations of Radio-Loud AGNs.pdf

a r X i v : a s t r o - p h / 9 8 1 1 0 1 7 v 2 8 N o v 1 9 9 8 ASCA Observations of Radio-Loud AGNs Rita M. Sambruna Michael Eracleous Department of Astronomy Astrophysics, The Pennsylvania State University 525 Davey Lab, University Park, PA 16802 and Richard F. Mushotzky NASA/GSFC, Code 662, Greenbelt, MD 20771 ABSTRACT We summarize the results of an X-ray spectroscopic survey of radio-loud AGNs observed with ASCA, using proprietary and archival data (public up to 1998 September). We briefly compare our results with those obtained for radio-quiet AGNs studied by other authors, and with the predictions of unified models. 1. Introduction One of the fundamental open problems of AGN research is the dichotomy between radio-loud and radio-quiet (RL/RQ) AGNs. While in both cases the ultimate source of power is thought to be accretion onto a massive black hole (Antonucci 1993; Urry Padovani 1995), the two classes exhibit subtle but systematic differences at all observed wavelengths, the most conspicuous being the ability of RL AGNs to form collimated, relativistic jets, in contrast to their RQ counterparts. The X-ray spectra of AGNs may hold the key to understanding the RL/RQ dichotomy. Since X-rays are produced in the innermost regions of the accretion flow, they allow us a direct view of the central engine where the jets form. Indeed, different models for the formation of jets require different structures for the central engines and thus make different predictions for the production of X-rays, e.g., the spinning black hole model of Blandford Znajek (1977) combined with the hydromagnetic wind model of Blandford Payne (1982), or the ion torus or advection-dominated disk of Rees et al. (1982) and Narayan Yi (1994,1995). It is thus encouraging that previous studies of RL AGNs with the Einstein IPC and EXOSAT found systematic differences, with RL sources being more X-ray-luminous and having flatter X-ray spectra (?Γ ～ 0.5) than RQ ones (Wilkes Elvis 1987; Lawson