X-Ray Properties of the Northern Galactic Cap Sources in the 58 Month Swift/BAT Catalog
Abstract
We present a detailed X-ray spectral analysis of the non-beamed, hard X-ray selected active galactic nuclei (AGNs) in the northern Galactic cap of the 58 month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGNs with b > 50°. This sky area has excellent potential for further dedicated study due to a wide range of multi-wavelength data that are already available, and we propose it as a low-redshift analog to the "deep field" observations of AGNs at higher redshifts (e.g., CDFN/S, COSMOS, Lockman Hole). We present distributions of luminosity, absorbing column density, and other key quantities for the catalog. We use a consistent approach to fit new and archival X-ray data gathered from XMM-Newton, Swift/XRT, ASCA, and Swift/BAT. We probe to deeper redshifts than the 9 month BAT catalog (langzrang = 0.043 compared to langzrang = 0.03 for the 9 month catalog), and uncover a broader absorbing column density distribution. The fraction of obscured (log N H >= 22) objects in the sample is ~60%, and 43%-56% of the sample exhibits "complex" 0.4-10 keV spectra. We present the properties of iron lines, soft excesses, and ionized absorbers for the subset of objects with sufficient signal-to-noise ratio. We reinforce previous determinations of the X-ray Baldwin (Iwasawa-Taniguchi) effect for iron Kα lines. We also identify two distinct populations of sources; one in which a soft excess is well-detected and another where the soft excess is undetected, suggesting that the process responsible for producing the soft excess is not at work in all AGNs. The fraction of Compton-thick sources (log N H > 24.15) in our sample is ~9%. We find that "hidden/buried AGNs" (which may have a geometrically thick torus or emaciated scattering regions) constitute ~14% of our sample, including seven objects previously not identified as hidden. Compton reflection is found to be important in a large fraction of our sample using joint XMM-Newton+BAT fits (langRrang = 2.7 ± 0.75), indicating light bending or extremely complex absorption. High-energy cutoffs generally lie outside the BAT band (E > 200 keV) but are seen in some sources. We present the average 1-10 keV spectrum for the sample, which reproduces the 1-10 keV X-ray background slope as found for the brighter 9 month BAT AGN sample. The 2-10 keV log(N)-log(S) plot implies completeness down to fluxes a factor of ~4 fainter than seen in the 9 month catalog. We emphasize the utility of this northern Galactic cap sample for a wide variety of future studies on AGNs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2013
- DOI:
- 10.1088/0004-637X/763/2/111
- arXiv:
- arXiv:1212.2957
- Bibcode:
- 2013ApJ...763..111V
- Keywords:
-
- galaxies: active;
- surveys;
- X-rays: galaxies;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in ApJ, 40 pages, 30 figures, 8 tables