The X‐Ray Properties of Active Galactic Nuclei with Double‐peaked Balmer Lines

Double-peaked Balmer-line profiles originate in the accretion disks of a fewpercent of optically selected AGN. The reasons behind the strong low-ionizationline emission from the accretion disks of these objects is still uncertain. Inthis paper, we characterize the X-ray properties of 39 double-peaked Balmerline AGN, 29 from the Sloan Digital Sky Survey and 10 low optical-luminositydouble-peaked emitters from earlier radio-selected samples. We find that theUV-to-X-ray slope of radio-quiet (RQ) double-peaked emitters as a class doesnot differ substantially from that of normal RQ AGN with similar UVmonochromatic luminosity. The radio-loud (RL) double-peaked emitters, with theexception of LINER galaxies, are more luminous in the X-rays than RQ AGN, ashas been observed for other RL AGN with single-peaked profiles. The X-rayspectral shapes of double-peaked emitters, measured by their hardness ratios orpower-law photon indices, are also largely consistent with those of normal AGNof similar radio-loudness. In practically all cases studied here, externalillumination of the accretion disk is necessary to produce the Balmer-lineemission, as the gravitational energy released locally in the disk by viscousstresses is insufficient to produce lines of the observed strength. In theAppendix we study the variability of Mrk 926, a double-peaked emitter withseveral observations in the optical and X-ray bands.Comment: 19 pages, 12 figures, accepted by Ap