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WGACAT - Catalog of PSPC WGA Sources (final version May 2000 / updated August 2000)

 HEASARC
Archive

Overview

WGACAT is a point source catalog generated from all ROSAT PSPC pointed observations. This catalog has been generated by N.E. White (HEASARC/GSFC), P. Giommi (SDC/ASI) and L. Angelini (HEASARC/GSFC) and is a private research effort, not related to the official catalogs generated by the ROSAT project. The WGACAT was made first publicly available in November 1994 through the HEASARC on-line service (White, Giommi and Angelini 1994), with a first minor revision in March 1995 (WGACAT95 hereafter). It was generated using all the public ROSAT PSPC pointed data available than, corresponding to 75 % of the entire set, and featured ~ 68000 detections of which 62000 were unique sources. The current version, released in May 2000 (see also the update section), is the final and complete version of WGACAT and includes the remaining sequences not processed in the WGACAT95. WGACAT (May 2000) contains about 88,000 detections, with more than 84,000 individual sources, obtained from 4160 sequences.

The catalog was generated using an optimized sliding cell detect algorithm in XIMAGE (first developed for the EXOSAT project). The inner and outer parts of the images were run separately, to maximize the sensitivity to source detection. This method is very sensitive in finding point sources, but can also find spurious sources where there is extended emission. We have visually inspected each detection, removed the obvious spurious cases and assigned a quality flag to each detection.

References

   * Dickey, J. M. & Lockman, F. J. 1990, ARAA, 28, 215.

   * White, N.E., Giommi, P, Angelini, L., HEAD meeting Nov. 1994

   * White, N.E., Giommi, P, Angelini, L., AAS Tucson (AZ) Jan. 1995.

Revision

The May 2000 release of WGACAT contains the following revisions compared to the WGACAT95: 
 * The quality check has been performed with a new scheme (see Quality
   section). All the individual detections have been visually inspected,
   and a new quality flag assigned.

 * In WGACAT95, many good sources were flagged bad if they were detected
   in a-) fields containing bright extended emission or b-) in the overlap
   region between the inner and outer regions. Quality checks for fields
   containing bright extended emission was done on the whole field
   rather than inspecting each single detection. This resulted in flagging
   as bad also good sources. These sources now have been restored.
   In the overlapping region, the edge effects combined with the presence of
   the inner support structure cause a spurious peak in the number of
   detections. In the 1995 version, this problem was taken care by excluding
   all detections in the outer region at a radius less than 21 arcmin, which
   resulted in removal of a number of good sources as well. Such sources
   have been restored by inspecting individual detections and by supressing
   only double-counted sources between inner and outer regions.

   This new quality check resulted in the recovery of many sources.
   For the WGACAT95 the total point sources with quality flag higher than 5
   is now 77154, compared to 68907 previously reported.

 * Not all the ROSAT data were publicly available when WGACAT95 was
   released. To complete WGACAT, an additional set of 516 new sequences
   (mostly REV2 data) was processed (WGACAT2 hereafter). This new processing
   produced an addition of ~8890 sources with quality flag higher than 5.
   An extra parameter, ``ORIGIN'', has been added in the catalog to
   indicate whether the detection is from the first processing, used to
   create WGACAT95 (ORIGIN is set to 1), or from the additional processing,
   WGACAT2 (ORIGIN is set to 2).

 * For detections obtained from REV1 data (mostly WGACAT95) any anomaly
   in the original file was investigated and compared with the
   corresponding REV2. The chi**2 test for variability, included in the
   WGACAT processing, was quite useful to reveal problems in the data and
   discover false sources. They were manifested as an exceptionally high
   variability associated with a source for a short time interval. These
   were typically caused by an incorrect assignment of the pointing direction
   in one of the time intervals included in a sequence, or due to the
   inclusion of a different pointing. In such cases the source detection
   and the variability are false and  these detections have been removed by
   assigning a quality flag of 3. The total of 86 sequences (~2% of the
   total) have been affected by these problems.

 * In WGACAT95 and WGACAT2, the distribution of good sources versus
   off-angle of the merged catalog
   showed a `lack' of sources between 12 arcmin and 17 arcmin offaxis
   radius.
   The PSF of the PSPC in the inner region of the detector is
   relatively steady, however at the edge of the inner region
   the PSF starts to degrade rapidly. The detection algorithm employed
   to generate WGACAT uses a fixed box-size for the entire inner region.
   This is reasonable up to ~ 12 arcmin where the PSF is almost constant,
   but a larger box size would be more appropriate after that.
   These ``missing sources'' are therefore due to the usage of a box-size
   optimized for the central region rather than the edge. To test that
   this was the cause of the ``missing sources'', the source detection
   was rerun in a portion of the inner region
   at off-axis radius > 8 arcmin, using a larger box size.
   This resulted in 2577 additional sources, after excluding double-counted
   detections with existing "in" and/or "out" region sources,
   with quality flag higher than 5 that fill in the ``gap'' between
   ~12 arcmin - 17 arcmin offaxis.  These sources are flagged in the
   parameter REGION as `i2', the position error has been assigned at 20
   arcsec and the data products associated are identified by "in2" in
   their filename. This extra processing was done only for the new 516
   sequences. It has not been run for the larger sample of sequences
   in WGACAT95.
   The current catalog has now 88621 sources with 84929 unique detection
   (unique is defined as sources are within 20 arcsec radius of each other),
   which includes the results from WGACAT95, WGACAT2 and the in2 processes.

 * In the course of this revision process, we became aware of a problem
   with the coordinates for 345 sequences in WGACAT95.
   This was caused by an error in converting the header of the old format
   event files into RDF format.
   This error caused an offset in the source declination up to 1 arcmin.
   This problem has been corrected.

 * Cross-correlations against other major catalogs have been rerun.
   Many of the catalogs used to cross-correlate WGACAT95 were updated
   and many new catalogs were available at the HEASARC.
   The total of 92 catalogs (in optical, infrared, radio, and X-ray) are
   now cross-correlated in the orders that can produce the best results.

 * Parameters such as FXFO, IPC_PSPC_RATIO, IPC_PSPC_RATIO_ERROR, AOX,
   and ARO have been recalculated reflecting the updates and changes in
   the relevant parameters.

 * The NH for each source position has been recalculated by utilizing
   the H I map by Dickey and Lockman (1990). The sky coverage of this map
   is complete in comparison with the Starke et al. (1984), used for
   WGACAT95, where the NH data were infeasible at Dec < -39 deg.

Processing

The catalog was generated using the ROSAT PSPC FITS event files. The processing of the ROSAT PSPC data was done using a c-shell script to run the XIMAGE X-ray image analysis package (available from the HEASARC). The WGACAT first version (Nov 1994) and revision (Mar 1995) used the US FITS event files, as they were stored in the archive, and the German files after reformatting to the US FITS event format. All files were also time ordered to allow a time variability search. The event files used for the WGACAT95 were all REV1 data. In the spring of 1998, to complete WGACAT, the processing pipeline was run on the additional sequences not available in the archive when WGACAT95 was first generated. These second batch of sequences were mostly REV2 data.

The ROSAT PSPC field was divided in two parts : the first includes the center of the field roughly up to the inner support structure at 19 arcmin radius. The second is the region outside the inner support and runs from 18 to 55 arc min. The background, point spread function and vignetting are very different for the inner and outer regions, and separating them gives a more sensitive source detection. The inner region was rebinned by a factor of 8, and the outer part by a factor of 20. To better follow the rapid change of the PSF, a third region, including data from 9-20 arcmin, was added to the pipeline when the second batch of sequences was processed. The results from this third region is only available for sequences processed in 1998 not for sequences processed in 1994. This region is identified as the "in2" region.

For all the detections hardness and softness ratios were calculated by splitting the PSPC band into three bands. For each detected source a chi**2 parameter related to the time variability has been calculated based on a KS test on the photon distribution.

Catalog Access

ASCII versions of the catalog has been found at https://heasarc.gsfc.nasa.gov/FTP/rosat/wgacat/catalogs/.

Cross Correlations

A cross-correlation of the WGACAT against 92 major catalogs has allowed a preliminary identification of known optical, radio, X-ray and infrared objects. The results of the cross-correlation is included as parameters in the WGACAT. Only a small fraction of the WGACAT (about 20%) found matches in the major available catalogs.

The catalogs used include: 

 * The Guide Star Catalog

 * The Einstein EMSS, IPC, HRI and Slew surveys

 * The EXOSAT HGLS catalog

 * The EUVE catalog

 * The HEAO 1 A3 catalog

 * The ROSAT all-sky survey (bright source catalog), HRI
   (release in May 2000, with 10861 high confidence detections.), WFC catalogs

 * The ROSAT PSPC source catalog by MPE (ROSPSPC released in May 2000)

 * The van Paradijs X-ray Binary catalog (XRBCAT)

 * The PMN, Dixon, Kuehr, VLA, PKS, MRC and
   the 6and 20cm North radio catalogs

 * The Lyne Radio Pulsar catalog

 * The IRAS PSC and FSC catalog

 * The Abell, Zwicky, HCG, M31, LMC/SMC,
   and globular cluster catalogs

 * The ngc2000, Huchra CfA Redshift, mcg, rc3, Hewitt and
   Burbridge QSO, Veron2000, ESO Uppsala, extragalactic catalogs

 * The Positions and Proper motions PPM, ACRS, HDEC, SAO,
   Variable Stars, Tycho, Hipparcos Catalogs, Herbig Emission-Line
   Star Catalog, CNS3 Nearby Stars (3rd Ed), the Bright Star, O,
   Carbon and Be Star catalogs

 * The Downes and Shara Cataclysmic Variable Catalogs

 * The MckSion White Dwarf catalog

 * The Simbad source list provided to the ROSAT project
Detailed descriptions for these catalogs can be found at https://heasarc.gsfc.nasa.gov/W3Browse/.

The full list of the cross-correlated catalogs are listed below using the names given in HEASARC Browse. 

  Radio catalogs: PULSAR, PKSCAT90, MRC, DIXON, KUEHR, PMN,
                  VLANEP, NORTH6CM, NORTH20CM

  Infrared catalogs: IRASPSC, IRASFSC

  Optical catalogs: ROSID, TYCHO, HIPPARCOS, SAO, HDEC, PPM,
                    ACRS, MACS, MCG, RC3, ESOUPP, ZCAT, NGC2000,
                    VSTARSUSP, VSTARS, ZWCLUSTERS, ABELL, HCG,
                    M31CLUSTRS, LMCCLUSTRS, SMCCLUSTRS, GLOBCLUST,
                    VERON2000, BSC5P, QSO, CPSTARS, GSC, WOOLLEY,
                    CNS3, PMSUCAT, HCGGALAXY, LBQS, BESTARS, HBC,
                    BATTEN, CVCAT, DUERBECK, CABSCAT, OSTARS, MCKSION,
                    M31STARS, SMCSTARS2, SMCSTARS, RITTERRBIN,
                    RITTERCV, RITTERLMXB, XRBCAT, HRASSCAT, RASSCNS3,
                    HYADESXRAY, RASSOB, RASSWD, RASSGIANT, RASSDWARF,
                    ORIONXSTAR, ROSATRQQ, ROSATRLQ

  X-ray and UV catalogs: A3, EXOHGLS, EUVECAT2, HRICFA, HRIDEEP,
                         IPCSLEW, IPC, EMSS, LMCXRAY, SMCXRAY,
                         IPCDEEP, IPCOSTARS, IPCLXLBOL, IPCULTSOFT,
                         ORIONXRAY, ROSWFC2RE, ROSATXUV, RASSHGSOFT,
                         M31XRAY, SMCROSXRAY, CHASFRXRAY, RASSBSC,
                         ROSHRI, ROSPSPC
The results of these correlations are written in various parameters for each database record. The parameters GSC, XID, OID and RID indicate if an identification has been made in the Guide star catalog or any of the X-ray, Optical and radio catalogs respectively (= 1 if it has). Parameters like redshift, VMAG, and others have been written for any WGACAT detection if these values were available in the original in the catalogs used for the cross-identification. Derived parameters such as FXFO (the optical and X-ray flux ratio) are also given for WGACAT detection with an optical cross-identification. The FX is a simple conversion, and should be used with care since it depends on column density and source spectrum. The H I column density is derived from Dickey and Lockman (1990) map and recorded for each source.

Completeness

The processed ROSAT PSPC sequences are the US and German/UK data available at HEASARC as of April 1998. These data cover the ~4 years pointed phase of the PSPC between June 1990 and September 1994. A total of 4160 sequences (ROR number 100000 - 999999) are included in the final version of WGACAT (May 2000), where 3644 sequences were processed for WGACAT95 and 516 are the additional sequences processed in April 1998. The data used for WGACAT95 are all REV1 event files while the additional sequences 503 out of 516 are REV2 data. PSPC observations with the boron filter are not included in WGACAT.

As of May 2000, the ROSAT public archive (ROSPUBLIC) contains 4705 sequences (100000 - 999999 excluding the boron filter observations and 1913 from the RASS data). The difference in the number of the sequences between the processed WGACAT data and the current ROSAT public archive is due to the "splitting" of the REV1 sequences into multiple files in the REV2 archive.

Regions

The inner and outer regions of the PSPC were treated separately. In the inner region within ~19 arcmin radius the PSF and vignetting are relatively constant, and the sensitivity is a maximum. In the outer region both the PSF and vignetting degrade rapidly and the sensitivity decreases. The parameter REGION indicates if the detection comes from the inner (region = i or i2) or outer (region = o) region.

Duplicate Detections

In the catalog the same source may appear more than once. This occurs because the field was observed more than once. If a source was observed on separate occasions in the inner region and in the outer areas, then its designation (see ROSAT NEWS No. 32) may be slightly different because of the lower positional accuracy in the outer region. Also nearby double sources may be blended in the outer region. It is advised, when possible, to always use the X-ray position determination for the detection nearest the center (the OFFSET parameter gives the off-axis position in arcmin).

WWW

There is a WGACAT website, https://heasarc.gsfc.nasa.gov/wgacat/wgacat.html, where latest information and links to publications about WGACAT are posted.

Quality

The XIMAGE detection algorithm can also find spurious sources caused by extended and/or bright emission. As part of the processing a gif image of the field was generated with the detected sources overlaid, plus an individual thumbnail image of the source itself. These were used during the quality check of the catalog. Each source in the catalog have been visually inspected via these images, and when necessary the original data were re-analysed. Obvious spurious sources caused by large extended structures, spurious detection caused by an anomaly in the event files have been flagged, and removed from the public catalog. There may still be subtle problems caused by low level diffuse emission. The gif images have been made available as part of the catalog, to allow a further quality check by interested users. From the on-line WWW HEASARC databases system the gif images can be viewed by clicking on the hyperlink of the GIF products. We have assigned a quality flag of each detection. This is written in the parameter QFLAG, and ranges from 0 to 12. A brief description for each quality flag is as follows:

A QFLAG of 12 indicates a secure detection of a point source.

A QFLAG of 11 is assigned to good detection located near the inner detector support structure at ~20 arcmin radius.

A QFLAG of 10 is assigned to good detection located at near the outer edge of detector or near the support structure of the detector at offaxis > 20 arcmin radius.

A QFLAG of 9 is assigned to good detections. This quality flag is used to indicate that the thumbnails have not an optimized rebinning for the source strength and the source appeared split with a separation of about 10 arcsec, well inside the 80% HPD of the PSF. These sources are mostly at large offaxis and low rate (< 1e-2 count/s).

A QFLAG of 8 is assigned to good detection. This quality flag is used to indicate that the thumbnails have not an optimized rebinning for the source strength and the source appeared split with a separation less 5 arcsec, well inside the 80% HPD of the PSF. These sources are mostly at small offaxis and low rate (< 1e-2 count/s).

A QFLAG of 7 indicates that the detection is located within bright background due to extended emission such as clusters, supernova remnants or near by bright X-ray binaries.

A QFLAG of 6 indicates that the detection is good but it is weak source.

A QFLAG of 5 indicates that the detection is good but the source may be extended or elongated.

A QFLAG of 4 is assigned to spurious detection caused by nearby bright sources and to spurious detected located either at (or near) the inner/outer support structure or the edge of the detector.

A QFLAG of 3 is assigned to specific case of false detection. These sources may result from a local arc in the detector caused by a temporary HV breakdown, interacting high energy particles, or by mystery pointing that interrupt the sequence. This flag also used as the indicator for supernova remnants that are extended over the field.

A QFLAG of 2 indicates that the observation was taken within the first 2 months of the mission (June-July 1990) where the processing and satellite were unstable. It is also assigned to suppress one of the double-counted sources detected in between "in", "in2", and "out" regions.

A QFLAG of 1 means a false detection caused by spurious detections due to extended emission from bright supernova remnants or X-ray binaries within the field of view.

A QFLAG of 0 means a false detection caused by spurious detections due to extended emission from clusters. Eight sequences have been accidentally processed in both the old and the new data sets. All entries in the old data set have been removed by assigning QFLAG = 0.

The users should note that there are now 13 QFLAGs (0 to 12) in comparison to 11 QFLAGs (0 to 10) in the WGACAT released in 1995. The additional QFLAGs were needed in order to reflect the complexity of the various types of the detections. The on-line catalog includes only sources with QFLAG >= 5.

Sensitivity

The PROBABILITY and SNR parameters record, respectively, the probability that the detection is due to chance and the signal to noise of the detection. These were set to be less than 1E-04 and greater than 2, respectively.

Available products

The processing produces for each sequence several products: 
 * a smoothed intensity image in GIF format with boxes
   showing each detection

 * a GIF format intensity image centered at each
   X/Y detected position

 * a FITS format image used to run the processing
   (inner and outer region)

 * a timing image (a new method for visualizing flux variations)
   in GIF format

 * a color image in GIF format (showing hardness variation across the image)

 * a GIF format lightcurve and background subtracted spectrum for each
  detected source

 * a FITS format source spectrum and events file for each detected source

 * an ancillary response file for each source

 * a FITS format background spectrum for the inner and outer region

 * a FITS format background event file (one for the inner and one for outer
   region) obtained by removing all sources detected
These products are also available for the in2 region for sequences processed in April 1998. The gif images can be accessed from both the command line and WWW versions of browse. For the former type `xv` and for the latter click on the hyperlink.

For each sequence two intensity maps are created one for the inner region (region descriptor CIRCLE(7860,7860,2295)) rebinned by a factor of 8 with a size of 656 X 656, and one for the outer region (region description CIRCLE(7860,7860,6660) - CIRCLE(7860,7860,2145)) rebinned by a factor of 20 with a size of 680. The maps are named as follows {xx}{nnnnnnn}_in.img or {xx}{nnnnnnn}_out.img, where xx is either rp for US data and wp for german data, nnnnnnn is the sequence number. An additional map (656 X 656 rebin by 8) is created by the in2 processing, run only on a limited number of sequences. The region description used is CIRCLE(7860,7860,2295)-CIRCLE(7860,7860,960) and the filenames follow the same convention of the others and are identified by "in2" (e.g. {xx}{nnnnnnn}_in2.img).

The colour image containing `colour` values, were calculated summing the PI value for each photon arrived at position x, y divided by 100 and normalized by the total count accumulated in that pixel. The maps are stored in GIF format. The GIF image contains on the left colour image and on the right the intensity image smoothed with overlayed the box of the detected sources together with a sky grid. The map are named as follow {xx}{nnnnnnn}_in_col.gif or {xx}{nnnnnnn}_out_col.gif (or {xx}{nnnnnnn}_in2_col.gif if available).

The timing images are a tool to help identify variable sources. The method consists in comparing the time arrival distribution of the photons collected in each pixel with the corresponding distribution of the entire image using a Kolmogorov-Smirnov (KS) test. The result of the KS test is a chi**2 value (with 2 d.o.f.) which is then used to assign an intensity value to each pixel. High intensity chi**2 values are assigned to pixels where the distribution of photon arrival times is not consistent with that of the entire image. The `time variability image` so constructed visually shows areas where strong time variations occurred. The map are named as follow {xx}{nnnnnnn}_in_time.gif or {xx}{nnnnnnn}_out_time.gif (or {xx}{nnnnnnn}_in2_time.gif if available).

For each sequence two sets of background file are available one for the inner region and for the outer region. Each set of background files include a background event file and a background spectrum. The inner background event file was obtained using the inner region descriptor (CIRCLE(7860,7860,2295)) and subtracting the contribution of all the detected sources. The outer background event file was obtained using the outer region descriptor (CIRCLE(7860,7860,6660) - CIRCLE(7860,7860,2145)) and subtracting the contribution of all the detected sources within that region. The box size used to subtract the source contribution is stored in the parameter HALF_BOX. The inner and outer background spectra are obtained using all the data in the inner or outer background event file respectively. The files are named as follow {xx}{nnnnnnn}_in_bg.evt and {xx}{nnnnnnn}_in_bg.pha or {xx}{nnnnnnn}_out_bg.evt {xx}{nnnnnnn}_out_bg.pha. Background files, event and spectral, are also available for the in2 region only on a limited number of sequences obtained removing all sources from the region CIRCLE(7860,7860,2295)-CIRCLE(7860,7860,960). They are named as {xx}{nnnnnnn}_in2_bg.evt and {xx}{nnnnnnn}_in2_bg.pha.

A spectrum and an event file for each detection are also available. These have been extracted using the optimize box size (see parameter HALF_BOX). The spectra are not background subtracted or rebinned. The 256 channels have been grouped in 32 channels. For each spectrum there is also available an ancillary response file created using the 'pcarf' software (see ROSAT package in the FTOOLS distribution). The response file used to generate the arf is written in the spectrum in the keyword RESPFILE. Spectrum, event file and ancillary response file are in FITS format. The naming convention used is {xx}{nnnnnnn}_{region}_{in_no}.{ext} where xx and nnnnnnn as the same meaning as listed above, region has value either 'in' or 'out' or 'in2', id_no has the value of the parameter ID_NO, and ext has value 'pha', evt and 'arf' for spectrum, event file and ancillary response.

A background subtracted spectrum and lightcurve plots are provided in GIF format. The spectrum plot has been obtained by reading into XSPEC source spectrum the appropriate background spectrum ('in' for an inner region source, 'out' for an outer region source and 'in2' for the 9-20 arcmin region), the response matrix and the ancillary file. The lightcurve plot consists in two panels containing the source (top) and the background lightcurves (lower). It has been created running XRONOS on the source event file and the appropriate background event file, using a binning of 300 seconds (occasionally 500 seconds was used). The source lightcurve shown is NOT background subtracted. The name convention used is {xx}{nnnnnnn}_{region}_{in_no}_evt.gif and {xx}{nnnnnnn}_{region}_{in_no}_pha.gif.

Missed fields

A few fields were not processed or do not appear in the catalog because: 
 * The detection algorithm fails in finding an optimum box size
   to get enough boxes free of excesses to calculate the background
   level. This occurs in 116 runs, for either inner or outer region.

 * The detection fails because too many excesses were found per
   region. The cut-off number was 10000 which was the size of the
   array that held the excesses. This occurs mainly when there was
   a bright source in the field (e.g. a bright X-ray binary), or bright
   extended emission. It effects in total 132 sequences either for
   the inner or outer region.

 * No sources are detected in either inner or outer region of 157
   sequences. This occurs mostly in sequences with a short exposure
   time of a few hundred seconds or less.

 * The event files were too big (>42Mb) (only few cases).

Update

The ROSAT consortium released on the 25 of May 2000 "The Second ROSAT source Catalog of pointing observations with the PSPC (ROSPSPC / 2RXP)" (ROSAT News No. 72). The WGACAT final version, released on 1 May 2000 was cross-correlated with the previous version of ROSPSPC (known also as ROSATSRC) released first in November 1994. On the 2 May 2000 (ROSAT News No. 71) the ROSAT consortium also released an update of the ROSAT HRI catalog containing 30 % more sources compared to the previous version released in August 1999 (ROSAT News No. 69). We re-run the cross-correlation process using these new catalogs and also the updated version of the VERON (VERON2000) catalog. All the parameters derived as result of the cross-correlation were updated and/or recalculate. The WGACAT now contains these new cross-correlations (1 August 2000).

Parameters

Name
Source designation within WGACAT. To distinguish these sources from those in other catalogs of the ROSAT archive, WGACAT sources use a designation such as 1WGA J1223.4-3751. WGA stands for White, Giommi, and Angelini, the authors of the catalog followed by the source coordinates given as `hrmn.m+/-ddmm'.

RA_1950
Source RA in 1950

Dec_1950
Source Dec in 1950

RA
Source RA (displayed at the current equinox year).

Dec
Source DEC (displayed at the current equinox year).

X_Pixel
Source X coordinate in original pixels (1-15360).

Y_Pixel
Source Y coordinate in original pixels (1-15360).

LII
Source Galactic longitude.

BII
Source Galactic latitude.

Count_Rate
The count rate has been corrected for vignetting and PSF. Those correction are energy dependent and the vignetting at 1 keV has been used. The count/sec are obtained using a constant value for the exposure across the field. This may underestimate the source count rate, if the source lies close to the inner support structure and sources detected at the border of the detector. The band used is channels 24-200 or 0.24-2.0 keV. The background subtracted source count rate in counts/s, corrected for the telescope vignetting and PSF. The counts are accumulated from PI bins 24-224 (0.24-2.0 keV).

Count_Rate_Error
Error on count rate.

Fx
X-ray flux using a constant correction factor of 1.5E-11 erg/s/cm**2 (0.05-2.5 keV). It is a crude approximation and the true flux will depend on the underlying spectral shape.

Vignet
Telescope vignetting correction. 1 is on axis and a higher value as the source was detected offaxis.

Error_Radius
90% confidence source error radius. This value has been set at 13" for the detections in the "in" region, at 20" for the detections in the "in2" region, and at 50" a for the "out" region detections. In most cases, especially on axis, it is probably closer to 10".

Half_Box
The optimum source half box size in arcsec. It has been used to calculate the total number of counts found in the box.

Ctr_RA
The image center RA. It corresponds to (X_PIXEL,Y_PIXEL=7860.0, 7860.0).

Ctr_Dec
The image center Dec. It corresponds to (X_PIXEL,Y_PIXEL=7860.0, 7860.0).

Ctr_Offset
The offset of the detected position in arcmin from the image center position (CTR_RA, CTR_DEC).

Target_RA
Target RA and Target DEC contain the coordinate, in equinox 2000, corresponding to pixels x=7680, y=7680 and it was typically the position of the primary target. This is different from CTR_RA.

Target_Dec
Target DEC and Target RA contain the coordinate, in equinox 2000, corresponding to pixels x=7680, y=7680 and it was typically the position of the primary target. This is different from CTR_RA.

Offset
The offset of the detected position in arcmin from the position given in TARGET_RA and TARGET_DEC.

Field_Name
Field Name

ROR
The ROR number and ranges from 100000 up to 999999.

Time
The start time of the observation as given in the keywords DATE-OBS and TIME-OBS of the event file.

End_Time
The end time of the observation as given in the keywords DATE-END and TIME-END of the event file.

Ndetect
Total number of detections in the image. Since each sequence has been processed individually for the inner or outer region, NDETECT is the total number of detections either in the inner or outer region. Similarly for the in2 processing NDETECT indicates the number of detections within the in2 region.

ID_No
Source number in the field. It increases outwards from the center of the image. This number is unique only with the processed region (in, in2, or out) and 3 sources can thus have the same ID_NO in a given field but with different REGION parameter (`i', `i2', or `o').

Imagefile
The FITS image file name (e.g., wp200594_out).

Eventfile
The name of the event file (e.g., wp200594).

ID
Unique source ID for the detection assigned as "xxnnnnnn_region_idno" where xx is `rp' for the US sequence and `wp' for the German/UK sequence, nnnnnn is the ROR number, region is `out' for the detection in the outer region and `in' or `in2' for the detections in the inner region, ID_NO is the source number detected in the given region of the field. ID is unique only within a given revision.

Probability
This contains the probability, calculated by XIMAGE, that the detection is due to a background fluctuation. The threshold was set at 1.0E-4.

SNR
Signal to noise ratio of the source. (threshold set at 2).

Qflag
Quality flag. 0-4 mean bad or false detections while 5-12 indicate good sources. The on-line catalog contains only records with QFLAG >= 5.

Region
The region of the ROSAT PSPC image in which the source is detected (i=in, i2=in2, and o=out).

Zoom
Rebinning factor of the image.

Bgnd
Background level given as counts/original-pixel/s.

Exposure
Exposure of field in seconds.

Softness_Ratio
Softness ratio from PI channels 11-39/40-85 (0.1-0.4/0.4-0.9 in keV).

Softness_Ratio_Error
Error on the softness ratio.

Hardness_Ratio
Hardness ratio from PI channels 86-200/40-85 (0.9-2.0/0.4-0.9 in keV).

Hardness_Ratio_Error
Error on the hardness ratio.

SR_Hard
Softness ratio from the hard band in PI channels 50-86/87-129 or in keV 0.5-0.9/0.9-1.3.

SR_Hard_Error
Error on SR HARD.

HR_Hard
Hardness ratio from the hard band in PI channels 130-240/87-129 or in keV 1.3-2.4/0.9-1.3.

HR_Hard_Error
Error on HR HARD.

Total_Counts
Total number of counts detected.

Total_Counts_Error
Error on TOTAL_COUNTS.

Low_Band
Number of counts in PI channels 11-39 (0.1-0.4 keV).

Low_Band_Error
Error on LOW_BAND.

Mid_Band
Number of counts in PI channels 40-85 (0.4-0.9 keV).

Mid_Band_Error
Error on MID_BAND.

High_Band
Number of counts in PI channels 86-200 (0.9-2.0 keV).

High_Band_Error
Error on HIGH_BAND.

Chi2
Chi**2 variability. CHI2 is obtained by comparing the time arrival distribution of the photons collected in each detection box with the corresponding distribution of the entire image using a Kolmogorov-Smirnov (KS) test. The result of the KS test is a CHI2 value (with 2 d.o.f.).

Photons
Not filled

Lc_Bin_Number
Not filled

Lc_Variance
Not filled

Lc_Exp_Variance
Not filled

Lc_Chi2
Not filled

Lc_Min
Not filled

Lc_Max
Not filled

Xid
Has a pre-ROSAT X-ray source ID been made? 1=yes.

XID_1
Name of the 1st X-ray ID. This parameter contains any match from the cross-correlated X-ray catalogs. Since the results of the cross- correlations from multiple catalogs are overwritten, the actual content of this parameter is the result from the last catalog cross-correlated.

XID_2
Name of the 2nd X-ray ID. This parameter contains any match from the Einstein catalogs. The actual content of the parameter is the result from the last Einstein catalog cross-correlated.

XID_3
Name of the 3rd X-ray ID. This parameter contains any match from the cross-correlated catalogs other than the Einstein, ROSHRI, and RASSBSC catalogs. The actual content of this parameter is the result from the last catalog cross-correlated.

XID_4
Name of the 4th X-ray ID. This parameter contains any match from RASSBSC or ROSHRI catalogs.

IPC_Count_Rate
Count rate detected by the Einstein IPC.

IPC_Count_Rate_Error
Error on the IPC count rate.

IPC_PSPC_Ratio
The IPC/PSPC count rate ratio.

IPC_PSPC_Ratio_Error
Error on the IPC/PSPC count rate ratio.

Oid
Has an optical id been made? 1=yes.

Oid_1
Name of the 1st optical ID. This parameter contains any match from the cross-correlated optical catalogs. Since the results of the cross-correlations from multiple catalogs are overwritten, the content is the result from the last catalog cross-correlated.

Oid_2
Name of the 2nd optical ID. This parameter contains any match from large Galactic source catalogs. The actual content is the result from the last catalog cross-correlated.

Oid_3
Name of the 3rd optical ID. This parameter contains any match from large extragalactic source catalogs. The actual content of the parameter is the result from the last catalog cross-correlated.

Oid_4
Name of the 4th optical ID. This parameter contains any match from small Galactic/extragalactic source catalogs. Matches from catalogs of clusters also included in this parameter.

Idned
Is it identified by NED ? 1=yes (not filled)

Idsimbad
Is it in SIMBAD ? 1=yes (not filled)

Vmag
V magnitude of the cross-correlated optical ID.

Fxfo
X-ray to the optical flux ratio. This parameter is derived as log10(FXFO) = (Vmag/2.5) + log10(FX) + 5.37.

Aox
Optical to X-ray slope. This parameter is derived as AOX = (0.4((-0.2/Sin(|BII|))+Vmag) + log10(FX) + 1.723)/(-2.605).

Redshift
Redshift of the counterpart.

Class
Source classification.

Gsc
Is it in the Guide Star Catalog ? 1=yes.

GSC_Sequence
GSC sequence number.

GSC_Region
GSC region number.

Qv_Mag
GSC quasi-V magnitude.

Qb_Mag
GSC quasi-B magnitude.

Ext
GSC extended flag.

Rid
Radio ID? 1=yes.

Rid_1
Name of the 1st radio ID. This parameter contains any match from the cross-correlated radio catalogs. Since the results of the cross-correlations from multiple catalogs are overwritten, the actual content is the result from the last catalog cross-correlated.

Rid_2
Name of the 2nd radio ID. This parameter contains any match from general radio source catalogs. The actual content of the parameter is the result from the last catalog cross-correlated.

Rid_3
Name of the 3rd radio ID. This parameter contains a match from radio source catalogs covering specific classes or regions in the sky. The actual content is the result from the last catalog cross-correlated.

Flux_80_cm
Radio flux (mJy) at 80 cm from the cross-correlation.

Flux_20_cm
Radio flux (mJy) at 20 cm from the cross-correlation.

Flux_6_cm
Radio flux (mJy) at 6 cm from the cross-correlation.

Sihi
Radio spectral index between 6 cm and 20 cm (not filled).

Aro
Radio optical index. It is derived as ARO = (0.4((-0.2/Sin(|BII|))+Vmag) + log10(F6)-6.248)/5.38 where F6 is the flux at 6cm.

Irid
Is an IRAS ID ? 1=yes.

Irname
IRAS name.

Flux_10_Micron
10 micron IRAS flux.

Flux_25_Micron
25 micron IRAS flux.

Flux_60_Micron
60 micron IRAS flux.

Flux_100_Micron
100 micron IRAS flux.

Idra
1950 RA of ID star. This is filled only if the catalog has particularly good positions e.g., Hipparcos.

Iddec
1950 Dec of ID star. This is filled only if the catalog has particularly good positions e.g., Hipparcos.

Idcat
Catalog from which ID coords obtained: Hipparcos.

Idoffset
Offset of ID star from ROSAT position in arcmin. Only given if IDRA and IDDEC are filled.

Del_RA
Delta RA from reference star, if IDRA is filled.

Del_Dec
Delta Dec from reference star, if IDDEC is filled.

Version
Version of WGACAT in which source first appeared (partially filled and replaced by ORIGIN).

MPE_Name
Name of the source as it appears in ROSPSPC.

Mpeid
The source appearance in the MPE ROSPSPC database released in 2000. If the source is within 15" MEPID is set to 1. If it is within 60" it is set to 2.

MPE_Count_Rate
Count rate in ROSPSPC.

MPE_Count_Rate_Error
MPE count rate error.

NH_21cm
NH for the source position derived from the Galactic HI cm-2 from Dickey & Lockman (1990).

BV_Color
B-V color taken from the optical counterpart.

Origin
Set to 1, if the source was already included in WGACAT95, otherwise it is set to 2.

Contact Person

Questions regarding the WGACAT database table can be addressed to the HEASARC Help Desk.
Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:36:45 EDT