SWUVOTSSC - Swift/UVOT Serendipitous Source Catalog, v1.1

Overview

The first version of the Swift UVOT Serendipitous Source Catalog (UVOTSSC) provides positions and magnitudes, as well as errors and upper limits of confirmed sources, for observations taken from the start of operations in 2005 until October 1st of 2010.

The first version of the UVOTSSC has been produced by processing the image data obtained from the Swift Ultraviolet and Optical Telescope (UVOT). The data processing was performed at the Mullard Space Science Laboratory (MSSL, University College London, U.K.) using Swift FTOOLS from NASA's High Energy Astrophysics Software package (HEASoft-6.11), with some customizing of the UVOT packages in order to get more complete source detection and to properly apply quality flags to those sources that were detected within the UVOT image artifacts. The total number of observations with 17'x17' images used for version 1 of the catalog is 23,059, giving 6,200,016 sources in total, of which 2,027,265 have multiple entries in the source table because they have been detected in more than one observation. Some sources were only observed in one filter. The total number of entries in the source table is 13,860,568. The S/N ratio for all sources exceeds 5 in at least one UVOT filter, the rest of the filters having a S/N greater than 3.

U, B, V, UVW2, UVM2 and UVW1 refer to the filter bandpasses defined in the UVOT Filterwheel section of the MSSL documentation at http://www.mssl.ucl.ac.uk/www_astro/uvot/uvot_instrument/filterwheel/filterwheel.html.

The initially released version of the catalog (2015) was done with the source identifier "SWIFTUVOT" for each source, and was made available in that form. The decision was subsequently made to rename the catalog sources by including the catalog version number. In addition, in a few instances multiple source IDs shared the same name (IAUNAME). They will be distinguished by having a letter a,b,c,.. appended to their name. Sources brighter than 0.96 counts per frame have not been included because their coincidence loss is too large to correct for.

This HEASARC table contains version 1.1 of the Swift UVOT source table and contains 13,860,568 entries for the individual detections of 6,200,016 sources. The HEASARC has changed the names of many of the parameters from those given in the original table. In such cases, we have listed the original names in parentheses at the end of the parameter descriptions given below. There is a second related table which gives a summary of the observations from which the UVOTSSC sources listed in this table have been detected and measured, which is available at the HEASARC as the SWUVOTSSOB table.

Catalog Bibcodes

2014Ap&SS.354...97Y
2014styd.confE..37P

References

Serendipitous UV source catalogues for 10 years of XMM and 5 years of Swift
    Yershov V.N.
    <Astrophys. Space Sci. 354, 97 (2014)>
    =2014Ap&SS.354...97Y
The Swift UVOT Serendipitous Source Catalogue - UVOTSSC (2005-2010), Version 1
    Page M., Yershov V., Breeveld A., Kuin N.P.M., Mignani R.P.,
    Smith P.J., Rawlings J.I., Oates S.R., Siegel M., Roming P.W.A.
   <Proc. Swift 10 Years of Discovery, held 2-5 December 2014 at
    La Sapienza University, Rome, Italy, 37 (2015)>
   =2015yCat.2339....0Y
   =2014styd.confE..37P (2015arXiv150306597P)

Provenance

This table was created by the HEASARC in May 2017 based upon the CDS Catalog II/339 file uvotssc1.dat.

Quality Flag Values for the UVOTSSC Catalog

The quality flag values are as follows:

Bit    Integer Meaning
Number Value
0      1       Cosmetic defects (BAD PIXELS) within the source region
1      2       Source on a READOUT STREAK
2      4       Source on a "SMOKE RING"
3      8       Source on a DIFFRACTION SPIKE
4     16       Source affected by MOD-8 noise pattern
5     32       Source within a "HALO RING"
6     64       Source near to a BRIGHT source
7    128       MULTIPLE EXPOSURE values within photometry aperture
8    256       Source within an EXTENDED FEATURE

Multiple flags are summed to give the final quality flag value. Examples of usage of this coding:

(1) Quality flag = 1 - Source contains one or more bad pixels,
(2) Quality flag = 3 - Source contains one or more bad pixels and
                       lies on a read-out streak,
(3) Quality flag = 7 - Source contains one or more bad pixels and lies on
                       a read-out streak and lies within a "smoke ring" region.

Notes on individual quality flags:

Bad Pixels (Quality bit number 1): A point source will have this flag set if any pixel within the photometry aperture, or any within the background annulus, has a corresponding pixel in the quality image with a non-zero value. Similarly, an extended source will have this flag set if any corresponding pixel in the quality image has a non-zero value.

Count Rate: If the count per frame exceeds 0.96 counts/frame, it cannot be corrected for coincidence loss and the magnitude will be suspect. These magnitudes (and other associated parameters) have been removed from the catalog. If no valid measurements are available for any filter the source has been removed entirely from the catalog.

Parameters

Entry_Number
This parameter contains a HEASARC-created unique sequential identification number for each entry in the catalog.

Obs_Sum_Number
This parameter provides the reference number of the observation summary given in the related auxiliary table SWUVOTSSOB (i.e., this is the entry number of the latter table). (N_SUMMARY)

ObsID
The unique Swift observation identification number corresponding to the observation in which the source was detected.

Num_Filters
The number of UVOT filters included in this source observation. (NFILT)

Source_Number
A unique source number throughout the UVOTSSC source catalog. (Please note that the number of entries in this table is larger that the total number of individual sources.) (SRCNUM)

Name
This parameter provides individual source identification strings in the conventions of the International Astronomical Union. For each source, its name starts with the string 'UVOTSSC1' characterizing the sources as obtained from the NASA Swift mission with the UVOT telescope, version 1. This string is followed by the Right Ascension and Declination coordinates for the epoch J2000.0 in the form 'JHHMMSS.s+DDMMSS'. Note that, because of problems with the rounding of positional coordinates, a single name can refer to more than one source number: there are 149 known such cases. They have been distinguished by having a letter a, b, c, etc. appended to their names. (IAUNAME)

RA
The Right Ascension of the UVOT source in the selected equinox. This was given in J2000.0 degrees to a precision of 10^-6 degrees in the original table.

RA_Error
The standard error in arcseconds of the source Right Ascension, i.e., (1/n)* sqrt(sum from 1 to n of err_k²), where err_k are the position errors of the n individual sources positions for the different filter. Please note that input errors from the individual source-list files are first converted from pixels to arcseconds. (RA_ERR)

Dec
The Declination of the UVOT source in the selected equinox. This was given in J2000.0 degrees to a precision of 10^-6 degrees in the original table.

Dec_Error
The standard error in arcseconds of the source Declination, i.e., (1/n)* sqrt(sum from 1 to n of err_k²), where err_k are the position errors of the n individual sources positions for the different filter. Please note that input errors from the individual source-list files are first converted from pixels to arcseconds. (DEC_ERR)

LII
The Galactic Longitude of the UVOT source.

BII
The Galactic Latitude of the UVOT source.

UVW2_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for neighboring sources was limited to a radius of 30 arcseconds.) (UVW2_SRCDIST)

UVM2_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for neighboring sources was limited to a radius of 30 arcseconds.) (UVM2_SRCDIST)

UVW1_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for neighboring sources was limited to a radius of 30 arcseconds.) (UVW1_SRCDIST)

U_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for neighboring sources was limited to a radius of 30 arcseconds.) (U_SRCDIST)

B_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for neighboring sources was limited to a radius of 30 arcseconds.) (B_SRCDIST)

V_Nn_Offset
The distance, in arcseconds, from this source to the closest neighboring source that was detected in the specified filter. (The search for the neighboring sources was limited to a radius of 30 arcseconds.) (V_SRCDIST)

Num_Individual_Obs
The number of individual observations (ObsIDs) in which the source was detected. This should correspond to the number of entries for that particular source in this table. (N_OBSID)

UVW2_Mag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (UVW2_SIGNIF)

UVM2_Mag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (UVM2_SIGNIF)

UVW1_Mag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (UVW1_SIGNIF)

Umag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (U_SIGNIF)

Bmag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (B_SIGNIF)

Vmag_Significance
The significance (signal-to-noise) of the source detection in the specified band, in sigma. (V_SIGNIF)

UVW2_Mag
The Vega magnitude of the source detection in the specified band. (UVW2_VEGAMAG)

UVW2_Mag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (UVW2_MAG_ERR)

UVM2_Mag
The Vega magnitude of the source detection in the specified band. (UVM2_VEGAMAG)

UVM2_Mag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (UVM2_MAG_ERR)

UVW1_Mag
The Vega magnitude of the source detection in the specified band. (UVW1_VEGAMAG)

UVW1_Mag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (UVW1_MAG_ERR)

Umag
The Vega magnitude of the source detection in the specified band. (U_VEGAMAG)

Umag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (U_MAG_ERR)

Bmag
The Vega magnitude of the source detection in the specified band. (B_VEGAMAG)

Bmag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (B_MAG_ERR)

Vmag
The Vega magnitude of the source detection in the specified band. (V_VEGAMAG)

Vmag_Error
The error in the corresponding magnitude of the source detection, a single error value being appropriate for both Vega magnitudes and AB magnitudes. (V_MAG_ERR)

UVW2_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (UVW2_ABMAG)

UVM2_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (UVM2_ABMAG)

UVW1_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (UVW1_ABMAG)

U_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (U_ABMAG)

B_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (B_ABMAG)

V_AB_Mag
The AB magnitude of the source detection in the specified band, computed from the Vega magnitude. (V_ABMAG)

UVW2_Flux
The source flux in the specified filter, in units of erg/s/cm²/Angstrom. The fluxes were derived using the count rate to flux conversion factors from Poole et al. (2008, MNRAS, 383, 627) which were based on GRB spectra. This differs slightly from the count rate to flux conversion factor based on Pickles (1998, PASP, 110, 863) star spectra expressed as a flux ratio. To convert the fluxes quoted here to fluxes calibrated with Pickles stars, the following multiplication factors should be used (the flux conversion factors given here are valid for UVOT B-V values redder than -0.36):

       Filter Central Wavelength  FWHM   Multiplication Factor
                    (nm)          (nm)   (Pickles/GRB)

          V        546.8          76.9       0.998
          B        439.2          97.5       0.893
          U        346.5          78.5       0.940
       UVW1        260.0          69.3       0.963
       UVM2        224.6          49.8       0.884
       UVW2        192.8          65.7       0.965