Spectral Statistics and Local Luminosity Function of a Complete Hard X-Ray Sample of the Brightest Active Galactic Nuclei

Abstract

We have measured the X-ray spectral properties of a complete flux-limited sample of bright active galactic nuclei (AGNs) from the HEAO-1 all-sky catalogs to investigate their statistics and provide greater constraints on the bright end of the hard X-ray luminosity function (HXLF) and the AGN population synthesis model of the X-ray background. Spectral studies using data from ASCA, XMM-Newton, and/or BeppoSAX observations have been made for almost all AGNs in this sample. The spectral measurements enable us to construct the neutral absorbing column density (log NH) distribution and separate HXLFs for absorbed (log NH[cm-2] > 21.5) and unabsorbed AGNs in the local universe. Our results show evidence of a difference in the shapes of the HXLFs of absorbed and unabsorbed AGNs in that the absorbed AGN HXLF drops more rapidly at higher luminosities than that of unabsorbed AGNs, similar to what has been previously reported. In the LX-NH plot we find no AGNs in the high-luminosity, high-intrinsic-absorption regime (log LX[ergs s-1] > 44.5 and log NH[cm-2] > 21.5) in our sample, in which we expect approximately five AGNs if we assume that the absorbed and unabsorbed AGNs have identical HXLF shapes. We also find that the fluxes observed with ASCA or XMM-Newton are smaller than that observed with HEAO-1 by a factor of 0.29 on average, which is expected for reobservation of sources with a factor of ~2.5 variability amplitude scale.