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WGACAT - Catalog of PSPC WGA Sources(final version May 2000 / updated August 2000) |
HEASARC Archive |
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.
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.
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.
The catalogs used include:
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, ROSPSPCThe 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.
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.
The May 2000 release of WGACAT contains the following revisions compared to the WGACAT95 :
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
Source RA (displayed at the current equinox year).
DEC
Source DEC (displayed at the current equinox year).
RA_1950
Source RA in 1950.
DEC_1950
Source DEC in 1950.
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 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
Field name as found in the event list (FITS keyword OBJECT).
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).
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_NAME
Name of the source as it appears in ROSPSPC.
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.