Abstract
Swift is a multi-wavelength observatory specifically designed for gamma-ray burst (GRB) astronomy that is operational since 2004. Swift is also a very flexible multi-purpose facility that supports a wide range of scientific fields such as active galactic nuclei, supernovae, cataclysmic variables, Galactic transients, active stars and comets. The Swift X-ray Telescope (XRT) has collected more than 150 Ms of observations in its first seven years of operations. We present the list of all the X-ray point sources detected in XRT imaging data taken in photon counting mode during the first seven years of Swift operations. All these point-like sources, excluding the Gamma-Ray Bursts (GRB), will be stored in a catalog publicly available (1SWXRT). We consider all XRT observations with exposure time > 500 s taken in the period 2005-2011. Data were reduced and analyzed with standard techniques and a list of detected sources for each observation was produced. A careful visual inspection was performed to remove extended, spurious and piled-up sources. Positions, count rates, fluxes and the corresponding uncertainties were computed. We have analyzed more than 35,000 XRT fields, with exposures ranging between 500 s and 100 ks, for a total exposure time of 140 Ms. The catalog includes ~ 89,000 entries, of which almost 85,000 are not affected by pile-up and are not GRBs. Since many XRT fields were observed several times, we have a total of ~36,000 distinct celestial sources. We computed count rates in three energy bands: 0.3-10 keV (Full, or F), 0.3-3 keV (Soft, or S) and 2-10 keV (Hard, or H). Each entry has a detection in at least one of these bands. In particular, we detect ~ 80,000, ~ 70,000 and ~ 25,500$ in the F, S and H band, respectively. Count rates were converted into fluxes in the 0.5-10, 0.5-2 and 2-10 keV bands. Some possible scientific uses of the catalog are also highlighted.
Highlights
The Swift gamma-ray burst Explorer (Gehrels et al 2004) is a NASA mission, successfully launched on 2004 Nov. 20
We have analyzed more than 35 000 X-ray Telescope (XRT) fields, with exposures ranging between 500 s and 100 ks, for a total exposure time of almost 140 Ms The catalog includes approximately 89 000 entries, of which almost 85 000 are not affected by pile-up and are not gamma-ray burst (GRB)
At the beginning of the satellite operations, approximately 56% of the Swift observing time was dedicated to GRB observations, and ∼26% divided up between target of opportunity (ToO, ∼8%) and “fill-in” observations
Summary
The Swift gamma-ray burst Explorer (Gehrels et al 2004) is a NASA mission, successfully launched on 2004 Nov. 20. Without losing too much relevant scientific information, in 2010 the GRB dedicated time dropped to ∼27% while ∼29% and ∼26% was allocated to ToO and Fill-in observations, respectively. This paper presents the 1SWXRT catalog, which consists of all the point-like sources detected by the XRT in its first seven years of operations (2005−2011). The reduction and analysis method is very similar to that adopted for the production of the “Swift Serendipitous Survey in deep XRT GRB fields” (Puccetti et al 2011), which comprises a list of sources detected in all Swift-XRT GRB fields with exposure times larger than 10 ks, observed by Swift between 2004 and 2008. Instead of summing all the observations related to the same field, we keep them separated, in order to build a catalog which retains information about the variability of our sources. Notes. (1) The first number of each entry shows the total observations per month. (2) The second number of each entry shows the total exposure time per month, in units of Ms
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