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Description
This table contains the 1SWXRT catalog of point sources detected by X-ray Telescope (XRT) on board of the Swift satellite during the first seven years of operation (Jan 2005 - Dec 2011). Swift is a NASA mission with international participation dedicated to gamma-ray burst study. It carries three instruments. The BAT is the large field of view instrument and operates in the 10-300 keV energy band; and two narrow field instruments, XRT and UVOT, that operate in the X-ray and UV/optical regime, respectively. The seven-year Swift-XRT point source catalog (1SWXRT) was built using all the observations performed by Swift-XRT in PC observing mode with an exposure longer than 500 s. The total number of observations considered is 35011, for an overall exposure time of ~140 Ms. Different observations with same pointing were not merged, but analyzed separately, thus retaining information about the variability of the catalogued sources. Most of the observations have short exposures. In fact, ~18% have t<sub>exp</sub> < 1 ks and ~77% have t<sub>exp</sub> < 5 ks. Only 7% of the observations have an exposure time > 10 ks, which are mostly (but not exclusively) fields associated with GRBs. The catalog was generated by running the detection algorithm in the XIMAGE package version 4.4.1 that locates the point sources using a sliding-cell method. The average background intensity is estimated in several small square boxes uniformly located within the image. The position and intensity of each detected source are calculated in a box whose size maximizes the signal-to-noise ratio. For each detection the catalog reports three count rates in the 0.3-3 (Soft), and 2-10 (Hard), and 0.3-10 (Full) keV energy bands. Each are corrected for dead times and vignetting using exposure maps and for the PSF. Hardness ratios are calculated using the three energy band and defined as HR = (c<sub>H</sub> - c<sub>S</sub>)/(c<sub>H</sub> + c<sub>S</sub>) where c<sub>S</sub> and c<sub>H</sub> are the count rates in the S(oft) and H(ard) bands, respectively. The catalog was cleaned from spurious and extended sources by visual inspection of all the observations. Count rates in the three bands were converted to 0.5-10, 0.5-2, and 2-10 keV observed fluxes, respectively. For the fluxes these energy bands were adopted to easy comparison with other X-ray catalogs (Watson, M. G. et al. 2009, A&A, 493, 339; Evans, I. N. et al. 2010, ApJ, 189, 37). The count rate to flux conversion was made using an absorbed power-law. The absorption is the Galactic hydrogen column density in the direction of the source and the photon spectral index has been estimated through the hardness ratio. Each row in the catalog is a detection not a unique source since the analysis was done by observation. Since multiple observations have covered the same part of the sky, a source may be detected more than once. The total number of detections is 84979 with an estimated 36000 unique sources as reported in the D'Elia et al. paper. The number of unique sources is derived by considering as one source all detections that have their positions within 12 arcsec. However, the catalog does not have a marker to identify all detections of a unique source. This database table was created by the HEASARC in November 2021 based on the electronic version available from the ASI Data Center <a href="https://www.asdc.asi.it/1swxrt/">https://www.asdc.asi.it/1swxrt/</a> and published in the Astronomy and Astrophysics Journal. This catalog is also available as <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/551/A142">CDS catalog J/A+A/551/A142</a>. The HEASARC added the id_number parameter, a counter to numerically identify each detection in the catalog (since the names of the detections are not unique), . Note that there is a discrepancy in the number of detections in the electronic version which has 84979 records and the number of detections reported in the paper (84992). This is a service provided by NASA HEASARC .
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