On the Fraction of X-Ray-obscured Quasars in the Local Universe

Recent wide area hard X-ray and soft Gamma ray surveys have shown that thefraction of X-ray obscured AGNs in the local universe significantly decreaseswith intrinsic luminosity. In this letter we point out that two correction haveto be made to the samples: 1) radio loud AGNs have to be excluded since theirX-ray emission might be dominated by the jet component; 2) Compton thicksources have to be excluded too since their hard X-ray and soft gamma rayemission are also strongly attenuated by Compton scattering. The soft gamma-rayselected AGN samples obtained by SWIFT and INTEGRAL provide the bestopportunity to study the fraction of obscured AGN in the local universe in theleast biased way. We choose these samples to check if the corrections couldalter the above result on the fraction of obscured AGNs. We find that beforethe corrections both samples show significant anti-correlation between L_X andN_H, indicating obvious decrease in the fraction of obscured AGNs withluminosity. However, after the corrections, we find only marginal evidence ofanti-correlation (at 98% confidence level) in the SWIFT sample, and no evidenceat all in the INTEGRAL sample which consists of comparable number of objects.We conclude that current samples only show a marginal decrease in the fractionof obscured AGNs in the local universe, and much larger samples are required toreach a more robust conclusion.Comment: 13 pages, including 4 figures, ApJ letter accepte