SWIF1SWXRT - The Seven-Year Swift-XRT Point Source Catalog (1SWXRT)
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 texp < 1 ks and ~77% have texp < 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 = (cH - cS)/(cH + cS) where cS and cH 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.
The seven year Swift-XRT point source catalog (1SWXRT) D'Elia V., et al <A&A 551, A142 (2013) > =2013A&A...551A.142D
Sequential, unique numerical identifier for each entry (detection) in this catalog.
Catalog source designation in the form 1SWXRT JHHMMSS.S+ddmmss.
Target designation based on the XRT field name.
Right Ascension of the source. The position was originally given in J2000 coordinates with a variable amount of precision up to 1.0e-08 deg.
Declination of the source. The position was originally given in J2000 coordinates with a variable amount of precision up to 1.0e-07 deg.
Galactic Longitude of the source. The HEASARC calculated this value by converting the J2000 position to Galactic coordinates.
Galactic Latitude of the source. The HEASARC calculated this value by converting the J2000 position to Galactic coordinates.
The positional error of the source at a 68% confidence level, in arcsec.
The XRT observation identifier.
Start time of the first observation of the source.
End time of the last observation of the source.
Total exposure time on the source, given in seconds.
The 0.3-10 keV count rate, or 90% upper limit, in count/s.
The one-sigma 0.3-10 keV count rate error in count/s. If count_rate_0p3_10 is an upper limit, this is set to -99.
The 0.5-10 keV flux, or 90% upper limit, in ergs/cm2/s.
The one-sigma 0.5-10 keV flux error in erg/cm2/s. If flux_0p5_10 is an upper limit, this is set to -99.
The 0.3-10 keV detection probability.
The 0.3-10 keV signal-to-noise ratio.
The 0.3-3 keV count rate, or 90% upper limit, in count/s.
The one-sigma 0.3-3 keV count rate error in count/s. If count_rate_0p3_3 is an upper limit, this is set to -99.
The 0.5-2 keV flux, or 90% upper limit, in ergs/cm2/s.
The one-sigma 0.5-2 keV flux error in ergs/cm2/s. If flux_0p5_2 is an upper limit, this is set to -99.
The 0.3-3 keV detection probability.
The 0.3-3 keV signal-to-noise ratio.
The 2-10 keV count rate, or 90% upper limit, in count/s.
The one-sigma 2-10 keV count rate error in count/s. If count_rate_2_10 is an upper limit, this is set to -99.
The 2-10 keV flux, or 90% upper limit, in ergs/cm2/s.
The one-sigma 2-10 keV flux error in ergs/cm2/s. If flux_2_10 is an upper limit, this is set to -99.
The 2-10 keV detection probability.
The 2-10 keV signal-to-noise ratio.
The hardness ratio, defined as (Hard-Soft)/(Hard+Soft) where Hard is the 2-10 keV count rate and Soft is the 0.3-3 keV count rate. This parameter is set to -99 if either Hard or Soft counts are missing.
The one-sigma hardness ratio error evaluated using the error propagation formulas from Bevington and Robinson, Data Reduction and Error Analysis for the Physical Sciences (1992; McGraw-Hill).
The Galactic hydrogen column density in the direction of the source in cm-2.
The energy spectral index, beta = Gamma - 1. This is set to -99 if either the soft or hard count rates are missing.
The one-sigma error in the energy spectral index.