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SIXSRVYCAT - Swift-INTEGRAL X-Ray (SIX) Survey Catalog



The supermassive black holes at the center of active galactic nuclei (AGNs) are surrounded by obscuring matter that can block nuclear radiation. Depending on the amount of blocked radiation, the flux from the AGN can be too faint to be detected by currently operating hard X-ray (above 15 keV) missions. At these energies, only ~1% of the intensity of the cosmic X-ray background (CXB) can be resolved into point-like sources that are AGNs. In this work, the authors address the question of undetected sources contributing to the CXB with a very sensitive and new hard X-ray survey: the Swift-INTEGRAL X-ray (SIX) survey, which is obtained with the new approach of combining the Swift/BAT and INTEGRAL/IBIS X-ray observations. The authors merge the observations of both missions, which enhances the exposure time and reduces systematic uncertainties. As a result, they obtain a new survey over a wide sky area of 6200 deg2 covering the region of the North Ecliptic Pole (NEP) and extending to the contiguous Coma region that is more sensitive than the surveys of Swift/BAT or INTEGRAL/IBIS alone. Their sample comprises 113 sources having S/N ratios of above 4.8 sigma: 86 AGNs (Seyfert-like and blazars), 5 galaxies, 2 clusters of galaxies, 3 Galactic sources, 3 previously detected unidentified X-ray sources, and 14 unidentified sources. The scientific outcome from the study of the sample has been properly addressed to study the evolution of AGNs at a redshift below 0.4. The authors do not find any evolution using the 1/Vmax method. Their sample of faint sources is a suitable target for the new generation of hard X-ray telescopes with focusing techniques.

Catalog Bibcode



The Deep Look at the Hard X-Ray Sky: The Swift-INTEGRAL X-Ray (SIX) Survey
    Bottacini E.,  Ajello M., Greiner J.
   <Astrophys. J. Suppl. Ser., 201, 34 (2012)>


This table was created by the HEASARC in August 2012 based on an electronic version of Table 2 from the reference paper which was obtained from the ApJS web site.


The name of the counterpart to the hard X-ray source. In order to identify this source sample, the authors cross-correlated it with the BAT catalog (Ajello et al. 2008, ApJ, 678, 102; Cusumano et al. 2010, A&A, 524, A64), the fourth IBIS/ISGRI catalog (Bird et al. 2010, ApJS, 186, 1), and the INTEGRAL reference catalog ( The authors also correlated the serendipitously detected objects with the ROSAT All-Sky Survey Bright Source Catalog (Voges et al. 1999, A&A, 349, 389). In addition, they made use of the NASA/IPAC Extragalactic Database (NED) and the SIMBAD Astronomical Database. Positional queries were performed considering possible counterparts within a radius of 6 arcminutes. Objects for which no counterparts were identified have been marked by a value of 'No ID' for this field.

The Right Ascension of the hard X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-4 degrees in the original table. The SIX point-spread function is symmetric and has a standard deviation of 6.8' (FWHM of 16').

The Declination of the hard X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-4 degrees in the original table. The SIX point-spread function is symmetric and has a standard deviation of 6.8' (FWHM of 16').

The Galactic Longitude of the hard X-ray source.

The Galactic Latitude of the hard X-ray source.

The redshift z of the counterpart of the hard X-ray source, as obtained by searching the archives.

The X-ray flux FX of the hard X-ray source in the 18 - 55 keV energy range, in erg cm-2 s-1. This was extracted from the SIX intensity map. The flux was computed by converting the count rate (counts) to physical units (erg cm-2 s-1) making use of the Crab as a calibration source. The Crab spectrum F(E) in units of (photons cm-2 s-1 keV-1) was assumed to be power-law shaped having a spectral index Gamma of -2.15 and a normalization factor of K = 10.17. The SIX sky coverage joins the best of both component surveys (IBIS/ISGRI and BAT), being very sensitive and covering the surveyed area very uniformly at the same time. The whole survey is complete to a flux level of 10-11 erg cm-2 s-1 while 50% of the SIX sky is surveyed to 8.5 x 10-12 erg cm-2 s-1 and the best flux sensitivity is 3.3 x 10-12 erg cm-2 s-1.

The signal-to-noise ratio of the hard X-ray source.

The logarithm of the rest-frame X-ray luminosity LX of the source in the 18 - 55 keV energy range, in erg s-1. This was computed using the relation LX = 4 pi DL2 FX/(1+z)2-Gamma, where Gamma is the spectral index obtained from the spectral fit, FX is the observed flux in the 18-55 keV energy range, and DL is the luminosity distance.

The logarithm of the absorbing column density NH towards the source, in H atoms cm-2. The authors searched in the literature for the absorption value of each AGN. When not available, they derived this parameter through the soft X-ray spectra. The soft X-ray data came from Chandra, Swift/XRT, and XMM-Newton observations. These instruments allowed them to connect their spectra to the hard X-ray spectra since their upper energy threshold is between 6 and 10 keV, depending on the instrument. The joint fit of the soft X-ray and hard X-ray spectra of the same source allowed derivation of the NH value in excess to the Galactic column hydrogen density. The authors used XSPEC 12 and the latest available response matrices for calibration to perform the fit. The best model for the fit was given by an absorbed power law with further absorption fixed to the Galactic column hydrogen density. All the other parameters were free to vary.

If the NH values were calculated in this work, this parameter is set to 1. If they were instead taken from the literature, this parameter is is set to 2-9. The reference codes for the absorbing column density NH, are as follows:

   1: This work;
   2: Burlon et al. 2011, ApJ, 728, 58;
   3: Tueller et al. 2008, ApJ, 681, 113;
   4: Cappi et al. 2006, A&A, 446, 459;
   5: Page et al. 2005, MNRAS, 364, 195;
   6: Winter et al. 2008, ApJ, 674, 686;
   7: Shu et al. 2007, ApJ, 657, 167;
   8: Dadina et al. 2010, A&A, 516, A9;
   9: Comastri et al. 2010, ApJ, 717, 787.

The general object classification of the counterpart.

The specific object type of the counterpart.

The HEASARC Browse object classification, based on the broad_type and subtype parameter values.

Contact Person

Questions regarding the SIXSRVYCAT database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Wednesday, 15-Aug-2012 13:33:59 EDT