NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-20 T22:44:56 PDT
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For refcode 2008ApJ...673...96A:
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Copyright by American Astronomical Society. Reproduced by permission
2008ApJ...673...96A 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.; Tueller, J. Abstract. 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 {alpha}=1.55+/-0.20 and a normalization of 9.6+/-1.9x10^-3^ AGNs deg^-2^ (or 396+/-80 AGNs all-sky) above a flux level of 2x10^-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 {sigma} 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 N_H_>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. Key words: Galaxies: Active, Surveys, X-Rays: Binaries, X-Rays: Galaxies
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