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 completeflux-limited sample of bright active galactic nuclei (AGNs) from theHEAO-1 all-sky catalogs to investigate their statistics and providegreater constraints on the bright end of the hard X-ray luminosityfunction (HXLF) and the AGN population synthesis model of the X-raybackground. Spectral studies using data from ASCA, XMM-Newton, and/orBeppoSAX observations have been made for almost all AGNs in this sample.The spectral measurements enable us to construct the neutral absorbingcolumn density (logNH) distribution and separate HXLFs forabsorbed (logNH[cm-2]>21.5) and unabsorbed AGNsin the local universe. Our results show evidence of a difference in theshapes of the HXLFs of absorbed and unabsorbed AGNs in that the absorbedAGN HXLF drops more rapidly at higher luminosities than that ofunabsorbed AGNs, similar to what has been previously reported. In theLX-NH plot we find no AGNs in the high-luminosity,high-intrinsic-absorption regime (logLX[ergss-1]>44.5 and logNH[cm-2]>21.5)in our sample, in which we expect approximately five AGNs if we assumethat the absorbed and unabsorbed AGNs have identical HXLF shapes. Wealso find that the fluxes observed with ASCA or XMM-Newton are smallerthan that observed with HEAO-1 by a factor of 0.29 on average, which isexpected for reobservation of sources with a factor of ~2.5 variabilityamplitude scale.