Hard X‐Ray Spectra of Broad‐Line Radio Galaxies from theRossi X‐Ray Timing Explorer

We present the results of hard-X-ray observations of four broad-line radiogalaxies (BLRGs) with the Rossi X-Ray Timing Explorer (RXTE). The originalmotivation behind the observations was to search for systematic differencesbetween the BLRGs and their radio-quiet counterparts, the Seyfert galaxies. Wedo, indeed, find that the Fe K-alpha lines and Compton "reflection" components,which are hallmarks of the X-ray spectra of Seyferts galaxies, are weaker inBLRGs by about a factor of 2. This observational result is in agreement withthe conclusions of other recent studies of these objects. We examine severalpossible explanations for this systematic difference, including beaming of theprimary X-rays away from the accretion disk, a low iron abundance, a smallsolid angle subtended by the disk to the primary X-ray source, and dilution ofthe observed spectrum by beamed X-rays from the jet. We find that a small solidangle subtended by the disk to the primary X-ray source is a viable andappealing explanation, while all others suffer from drawbacks. We interpretthis as an indication of a difference in the inner accretion disk structurebetween Seyfert galaxies and BLRGs, namely that the inner accretion disks ofBLRGs have the form of an ion-supported torus or an advection-dominatedaccretion flow, which irradiates the geometrically thin outer disk.Comment: 26 pages including figures and tables. To appear in the Astrophysical Journal, vol. 537, July 10, 200