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 few percent of optically selected active galactic nuclei (AGNs). The reasons behind the strong low-ionization line emission from the accretion disks of these objects are still uncertain. In this paper, we characterize the X-ray properties of 39 double-peaked Balmer line AGNs, 29 from the Sloan Digital Sky Survey and 10 low optical luminosity double-peaked emitters from earlier radio-selected samples. We find that the UV-to-X-ray slope of radio-quiet (RQ) double-peaked emitters as a class does not differ substantially from that of normal RQ AGNs with similar UV monochromatic luminosity. The radio-loud (RL) double-peaked emitters, with the exception of low-ionization nuclear emission-line region (LINER) galaxies, are more luminous in the X-rays than RQ AGNs, as has been observed for other RL AGNs with single-peaked profiles. The X-ray spectral shapes of double-peaked emitters, measured by their hardness ratios or power-law photon indices, are also largely consistent with those of normal AGNs of similar radio loudness. In practically all cases studied here, external illumination of the accretion disk is necessary to produce the Balmer line emission, as the gravitational energy released locally in the disk by viscous stresses is insufficient to produce lines of the observed strength. In the Appendix we study the variability of Mrk 926, a double-peaked emitter with several observations in the optical and X-ray bands.