- ID:
- ivo://nasa.heasarc/swift2sxps
- Title:
- Swift-XRT Point Source Catalog (2SXPS)
- Short Name:
- SWIFT2SXPS
- Date:
- 10 May 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the second Swift X-ray Point Source (2SXPS) catalog of detections by the Swift X-ray Telescope (XRT) used in Photon Counting (PC) mode in the 0.3-10 keV energy range. Swift is a NASA mission with international participation dedicated to the 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 overall 2SXPS catalog characteristics are as follows: <pre> Data included 2005 Jan 01 - 2018 August 01 Sky coverage 3,790 square degrees Typical Sensitivity (0.3-10 keV) 2x10<sup>-13</sup> erg cm<sup>-2</sup> s<sup>-1</sup> (observations) 4x10<sup>-14</sup> erg cm<sup>-2</sup> s<sup>-1</sup> (stacked images) Typical position error 5.6" (90% confidence radius, including systematics) Detections 1,091,058 Unique sources 206,335 Variable sources 82,324 Uncatalogued sources 78,100 False positive rate Flag=Good 0.3% Flag=Good/Reasonable 1% Flag=Good/Reasonable/Poor <10% </pre> This catalog enhances the 1SXPS catalogue (Evans, P. A., et al. 2014, ApJS, 210, 8) in different ways. The 2SXPS catalog uses an improved Point Spread Function (PSF) and pile-up models, a better source detection pipeline that includes a technique to model the effects of stray light, and tests to automatically avoid diffuse emission and ~six years more data. The results are that the 2SXPS catalog contains 50% more temporal coverage than 1SXPS, a sky coverage of 3790 square deg almost double compare to the 1SXPS (1905 square Degree) and ~30% more sources compared to the 1SXPS. The Swift XRT observations were filtered to remove times when: a) data were contaminated by scattered light from the daylight side of the Earth; b) the on-board astrometry derived from the images obtained by the Swift UV/Optical telescope was unreliable; and c) observations with less than 100s of PC mode. The 127519 observations included in the catalog provide a total usable exposure is 266.5 Ms. A Swift observation is a collection of snapshots and the source detection algorithm was run on individual observation as well as on stacked images. The latter were generated on a grid of 2,300x2,300 pixels (~ 90'x90') to ensure that every overlap between observations is in at least one stacked image. A total of 14628 stacked images were generated. Each record corresponds to a unique source which characteristics are described with 230 parameters. The catalog reports for each source rates in four energy band (0.3-10.keV, 0.3-1. keV, 1-2 keV and 3-10 keV), background rates, variability for each energy band, two hardness ratio, peak rate and several spectral parameters. The hardness ratios are defined as follows: <pre> HR1 = (M-S)/(M+S) where M and S are the medium (1-2 keV) and soft (0.3-1 keV) band count rates HR2 = (H-M)/(H+M) where H and M are the hard (2-10 keV) and medium (1-2 keV) band count rates </pre> and they are calculated using all observations. The peak rate is determined using three different timescale: the count rate considering all the observations (see parameters rates in this database), the count rate in each observation (not reported in this database) and the count rate in each snapshot (not reported in this database). The peak rate is the rate +/- error from the timescale which has the highest 1-sigma lower-limit on the count rate. Spectral parameters and source flux are estimated using three different methods for two spectral models, a power-law and APEC (see Smith et al., 2001, ApJL, 556, L91). Not all sources have values for all three methods. The parameters starting with "fix" are defined for every source and uses fixed spectral model parameters: a photon index of 1.7 for a power-law model, a temperature of kT=1keV for the APEC model and for both models uses the Galactic absorption listed in the parameter "nh". The parameters starting "intr" have been inferred from the hardness ratio. Look-up tables containing (HR1, HR2, NH, photon index) and (HR1, HR2, NH, kT) are pre-calculated for the power-law and APEC models. If the source HR1 and HR2 are close to the values in the table, spectral parameters are derived by interpolating the HR1 and HR2 in the look-up tables that are close to the HR1 and HR2 of the source. The parameters starting with "fit" have been derived from fitting an actual source spectrum in XSPEC and they are only available for the brightest sources (>50 net counts, and at least one detection in a single observation). The parameters fields starting with "pow" and "apec" report the values from the 'best' of these methods. The parameters "which_pow" and "which_apec" indicates which of the three methods are reported. The catalog also includes flags derived from the cross-correlated with other source catalogs. The catalogs and their reference sources are as follows: <pre> * AllWISE: <a href="https://wise2.ipac.caltech.edu/docs/release/allwise/">https://wise2.ipac.caltech.edu/docs/release/allwise/</a> * ROSAT HRI: <a href="https://heasarc.gsfc.nasa.gov/docs/rosat/rra/RRA.html">https://heasarc.gsfc.nasa.gov/docs/rosat/rra/RRA.html</a> * SDSS Quasar Catalog DR14: Paris et al., 2018, A&A, 613, 51 (<a href="https://www.sdss.org/dr14/algorithms/qso_catalog/">https://www.sdss.org/dr14/algorithms/qso_catalog/</a>) * 2MASS: Skrutskie et al., 2006, AJ, 131, 1163 * 2CSC: accessed via the CSCView Tool at <a href="https://cxc.harvard.edu/csc/about.html">https://cxc.harvard.edu/csc/about.html</a> (1CSC paper: Evans et al., 2010, ApJS, 189, 37) * 1SWXRT: Evans et al., 2014, ApJS, 210,8 * 1SXPS: D'Elia et al., 2013, A&A, 551, 142 * 2RXS: Boller et al., 2016, A&A, 588, 103 * 3XMM-DR8: <a href="http://xmmssc.irap.omp.eu/Catalogue/3XMM-DR8/3XMM_DR8.html">http://xmmssc.irap.omp.eu/Catalogue/3XMM-DR8/3XMM_DR8.html</a> (3XMM paper: Rosen, Webb, Watson et al., 2016, A&A, 590, 1) * 3XMM Stack: Traulsen et al., 2019, A&A, 642, 77 * SwiftFT: Puccetti et al. 2011, A&A,528, A122 * XMM SL2: Saxton et al., 2008, A&A 480, 611 * XRTGRB: Evans et al, 2009, MNRAS, 397, 1177 (<a href="https://www.swift.ac.uk/xrt_positions">https://www.swift.ac.uk/xrt_positions</a>) * USNOB1: Monet et al., 2003, AJ, 125, 984 </pre> The 2SXPS paper (Evans et al. 2020 ApJS, 247,54) describes in detail the methodology of stacking images, background modeling, point spread function mapping, stray light detection and corrections, data filtering techniques and processing. The 2SXPS catalog has a dedicated website at <a href="https://www.swift.ac.uk/2SXPS">https://www.swift.ac.uk/2SXPS</a>. This database table was created by the HEASARC in November 20201 based on the electronic version delivered to the HEASARC by the Leicester University. The catalog has a dedicated website at <a href="https://www.swift.ac.uk/2SXPS">https://www.swift.ac.uk/2SXPS</a>. The version available from the HEASARC corresponds to the catalog designated as "All" on the Leicester website. This is a service provided by NASA HEASARC .
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- ID:
- ivo://nasa.heasarc/swif1swxrt
- Title:
- The Seven-Year Swift-XRT Point Source Catalog (1SWXRT)
- Short Name:
- SWIF1SWXRT
- Date:
- 10 May 2024
- Publisher:
- NASA/GSFC HEASARC
- 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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