Astrophys. J., 673, 96-113 (2008/January-3)
The Swift BAT X-ray survey. III. X-ray spectra and statistical properties.
AJELLO M., RAU A., GREINER J., KANBACH G., SALVATO M., STRONG A.W., BARTHELMY S.D., GEHRELS N., MARKWARDT C.B. and TUELLER J.
Abstract (from CDS):
In this concluding part of the series of three papers dedicated to the Swift BAT hard X-ray survey (BXS), we focus on the X-ray spectral analysis and statistical properties of the source sample. Using a dedicated method to extract time-averaged spectra of BAT sources, we show that Galactic sources have, generally, softer spectra than extragalactic objects and that Seyfert 2 galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert galaxies is consistent with a power-law with a photon index of 2.00±0.07. The cumulative flux-number relation for the extragalactic sources in the 14-170 keV band is best described by a power-law with a slope α=1.55±0.20 and a normalization of 9.6±1.9x10–3 AGNs/deg2 (or 396±80 AGNs all-sky) above a flux level of 2x10–11 ergs/cm2/s (∼0.85 mcrab). The integration of the cumulative flux per unit area indicates that BAT resolves 1%-2% of the X-ray background emission in the 14-170 keV band. A subsample of 24 extragalactic sources above the 4.5 σ detection limit is used to study the statistical properties of AGNs. This sample is composed of local Seyfert galaxies (z=0.026, median value) and ∼10% blazars. We find that 55% of the Seyfert galaxies are absorbed by column densities of NH>1022 H atoms/cm2 but that none is genuinely bona fide Compton thick. This study shows the capabilities of BAT to probe the hard X-ray sky to the millicrab level.
Galaxies: Active - Surveys - X-Rays: Binaries - X-Rays: Galaxies
VizieR on-line data:
<Available at CDS (J/ApJ/673/96): table1.dat table1.tex>
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