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The Swift BAT X-Ray survey. III. X-Ray spectra and statistical properties

Ajello, M. and Rau, A. and Greiner, J. and Kanbach, G. and Salvato, M. and Strong, A. W. and Barthelmy, S. D. and Gehrels, N. and Markwardt, C. B and Tueller, J. (2008) The Swift BAT X-Ray survey. III. X-Ray spectra and statistical properties. Astrophysical Journal, 673 (1). pp. 96-113. ISSN 0004-637X.

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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 ± 1.9 x 10^-3 AGNs deg^−2 (or 396 ± 80 AGNs all-sky) above a flux level of 2 x 10^−11 ergs cm^−2 s^−1 (~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>10^22 H atoms cm^−2 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.

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Salvato, M.0000-0001-7116-9303
Additional Information:© 2008. The American Astronomical Society. Received 2007 July 18; accepted 2007 September 26. M.A. acknowledges N. Gehrels and the BAT team for their hospitality, M. Capalbi for assistance during BeppoSAX and Swift XRT data analysis, N. Cappelluti for useful discussions on the source count distribution derivation, R. Mushotzky for valuable suggestions, and the anonymous referee for his comments, which helped improve the paper. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, of data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA’s Goddard Space Flight Center, of the SIMBAD Astronomical Database, which is operated by the Centre de Donneés astronomiques de Strasbourg, of the Sloan Digital Sky Survey (SDSS) managed by the Astrophysical Research Consortium (ARC) for the Participating Institutions, and of the ROSAT All Sky Survey mantained by the Max-Planck-Institut für extraterrestrische Physik.
Subject Keywords:galaxies : active; surveys; X-rays : binaries; X-rays : galaxies
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Record Number:CaltechAUTHORS:AJEapj08a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12007
Deposited By: Marie Noren
Deposited On:24 Nov 2008 22:47
Last Modified:03 Oct 2019 00:24

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