SWXCSCAT - Swift X-Ray Telescope Cluster Survey Catalog
From the entire Swift XRT archive in the period 2005 February-2012 November, the authors have selected all the fields that can be used to build an unbiased, serendipitous X-ray cluster catalog.
The Swift X-ray telescope Cluster Survey. III. Cluster catalog from 2005-2012 archival data. Liu T., Tozzi P., Tundo E., Moretti A., Rosati P., Wang J.-X., Tagliaferri G., Campana S., Giavalisco M. <Astrophys. J. Suppl. Ser., 216, 28 (2015)> =2015ApJS..216...28L (SIMBAD/NED BibCode) The Swift X-ray Telescope Cluster Survey. II. X-ray spectral analysis. Tozzi P., Moretti A., Tundo E., Liu T., Rosati P., Borgani S., Tagliaferri G., Campana S., Fugazza D., D'Avanzo P. <Astron. Astrophys., 567, A89-89 (2014)> =2014A&A...567A..89T The Swift X-ray Telescope Cluster Survey: data reduction and cluster catalog for the GRB fields. Tundo E., Moretti A., Tozzi P., Teng L., Rosati P., Tagliaferri G., Campana S. <Astron. Astrophys. 547, A57 (2012)> =2012A&A...547A..57T
The Swift X-ray Cluster Survey (SWXCS) galaxy cluster candidate source name, being a J2000.0 position-based source designation registered with the CDS Dictionary of Nomenclature of Celestial Objects, viz., 'SWXCS JHHMMSS+DDMM.m'. This format is different from that used in Paper I (Tundo et al. 2012), but has already been used in Paper II (Tozzi et al. 2014). Note that the sources presented in Paper I keep the same names as used in Paper II, although the new positions typically differ by ~ 5".
This flag parameter is set to 'I' to indicate that a source was included in the first release of the SWXCS (Tundo et al. 2012, A&A, 547, A57).
The Right Ascension of the centroid of the galaxy cluster candidate in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table. The centroid is defined as the weighted median position of the 27 brightest pixels in the source region (each pixel is weighted by its density which equals to the pixel value divided by the Voronoi cell area).
The Declination of the centroid of the galaxy cluster candidate in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-6 degrees in the original table. The centroid is defined as the weighted median position of the 27 brightest pixels in the source region (each pixel is weighted by its density which equals to the pixel value divided by the Voronoi cell area).
The Galactic Longitude of the galaxy cluster candidate.
The Galactic Latitude of the galaxy cluster candidate.
The effective exposure time teff at the position of the source, in seconds, computed as given in Equation (1) of the reference paper, i.e., as the sum over i of ni divided by the sum over i of ni/ti, where i is the index of the filled pixels within the source extraction region, ni is the photon count in the ith pixel, and ti is the corresponding value in the vignetted exposure map.
The value of the Galactic neutral Hydrogen (H I) column density, in units of H atoms cm-2, as found in the Leiden/Argentine/Bonn radio survey (Kalberla et al. 2005, A&A, 440, 775).
The effective radius Reff, in arcseconds, defined such that pi * Reff2 equals the source extraction area (which has no a priori constraints on its shape).
The net counts Nnet measured in the soft band (0.5 - 2.0 keV) image by EXSdetect inside the source extraction region found by the VT+FOF method, after background subtraction and removal of unresolved sources. At present, no correction is applied to compensate for the lost diffuse emission in the region of the removed unresolved source.
The 1-sigma error in the net counts Nnet measured in the soft band (0.5 - 2.0 keV). This is computed as the square root of (Ntot + Nbkg), where Nbkg is the count of background photons and Ntot = Nnet + Nbkg.
The signal-to-noise ratio (S/N) in the soft band, computed as the net counts divided by the associated error.
The estimated soft-band flux S in units of erg cm-2 s-1. To compute the flux for each field, the authors estimate the energy conversion factor (ECF) in the 0.5 - 2.0 keV band, taking into account Galactic absorption in this field, assuming a hot diffuse gas emission model with a temperature of 5 keV, a metal abundance of 0.3 solar, and a redshift of z = 0.4. As shown in Paper I, the ECF depends weakly on the spectral parameters. The flux of each source is calculated as S = Nnet * ECF/teff.
The one-sigma error in the flux is measured by propagation, considering the error in the net counts and a 4% systematic error in the ECF due to the typical uncertainty in the actual spectral shape of each source (see Paper I). More accurate fluxes will be available from the X-ray spectral analysis of these sources, which is postponed until a forthcoming paper (A. Moretti et al., in preparation).