The Swift X-ray Telescope Cluster Survey III: Cluster Catalog from
  2005-2012 Archival Data
  We present the Swift X-ray Cluster Survey (SWXCS) catalog obtained using
archival data from the X-ray telescope (XRT) on board the Swift satellite
acquired from 2005 to 2012, extending the first release of the SWXCS. The
catalog provides positions, soft fluxes, and, when possible, optical
counterparts for a flux-limited sample of X-ray group and cluster candidates.
We consider the fields with Galactic latitude |b| > 20 degree to avoid high HI
column densities. We discard all of the observations targeted at groups or
clusters of galaxies, as well as particular extragalactic fields not suitable
to search for faint extended sources. We finally select ~3000 useful fields
covering a total solid angle of ~400 degree^2. We identify extended source
candidates in the soft-band (0.5-2keV) images of these fields using the
software EXSdetect, which is specifically calibrated for the XRT data.
Extensive simulations are used to evaluate contamination and completeness as a
function of the source signal, allowing us to minimize the number of spurious
detections and to robustly assess the selection function. Our catalog includes
263 candidate galaxy clusters and groups down to a flux limit of 7E-15
erg/cm^2/s in the soft band, and the logN-logS is in very good agreement with
previous deep X-ray surveys. The final list of sources is cross-correlated with
published optical, X-ray, and SZ catalogs of clusters. We find that 137 sources
have been previously identified as clusters, while 126 are new detections.
Currently, we have collected redshift information for 158 sources (60% of the
entire sample). Once the optical follow-up and the X-ray spectral analysis of
the sources are complete, the SWXCS will provide a large and well-defined
catalog of groups and clusters of galaxies to perform statistical studies of
cluster properties and tests of cosmological models.
