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ROSATCAT 

	     **** Fisrt reference on ROSATCAT ****
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=                                                                       =
=              ROSAT NEWS No. 32   ---      1-Nov-1994                  =
=                                                                       =
=-----------------------------------------------------------------------=
=                 ROSAT Scientific Data Center at the                   =
=       Max-Planck-Institut fuer Extraterrestrische Physik (MPE)        =
=               Postfach 1603, D-85740 Garching, Germany                =
=-----------------------------------------------------------------------=
=  e-mail addresses (Uli Zimmermann):                                   =
=   rosat_svc@mpe-garching.mpg.de (Internet) or  MPE::ROSAT_SVC (SPAN)  =
=  ROSAT Service Area (including ROSAT Data Archive):                   =
=   ftp rosat_svc.mpe-garching.mpg.de      user: anonymous              =
=   WWW address:  http://rosat_svc.mpe-garching.mpg.de/                 =
=   interactive account (including ROSAT Result Archive):               =
=     telnet xray.mpe-garching.mpg.de  user: xray  no password          =
=-----------------------------------------------------------------------=
=  XUV Center: 29382::GXUVDC or  GXUVDC@AIT.PHYSIK.UNI-TUEBINGEN.DE     =
=   WFC Archive access via telnet/ftp ait.physik.uni-tuebingen.de       =
=                                user: xuv  (password: xuv_archive)     =
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SATELLITE STATUS

No major problems were encountered during the last month.

THIRD ROSAT WORKSHOP at MPE

More than 100 participants of 30 research institutions attended the workshop to discuss actual ROSAT results and data evaluation issues. The directory general/workshop in the ROSAT Service Area contains the final list of the participants (including email addresses) and the program.

THE FIRST ROSAT SOURCE CATALOG

During the ROSAT workshop at MPE on October 26, 1994 Wolfgang Voges announced on behalf of the ROSAT Consortium (MPE-Garching, GSFC/SAO-US, and WFC-Consortium-UK) the public release of "THE FIRST ROSAT SOURCE CATALOGUE OF POINTED OBSERVATIONS WITH THE PSPC". This catalogue contains 50,408 sources from 2876 pointed observations. For each source the following properties are provided: the observation number, the ROSAT name, the position in equatorial and in galactic co-ordinates, four positional errors (intrinsic, systematic, boresight, and total), the source count-rate and its error, the background countrate, exposure time, hardness-ratios HR1 and HR2 and their errors, extent and likelihood of extent, likelihoods of the map-detect algorithm and of the maximum-likelihood detection algorithm, flags to indicate in which energy band and by what algorithm the source was detected, the detection cell size, the off-axis radius, the distances to the nearest rib and source (before and after removal of ambiguous sources), and a source confusion flag (set if another source is within 2.1*FWHM of the point-spread function).
This catalogue contains observations which have been performed until the end of May 1993 and which are in the public archive. A visual inspection of all soft and hard images, and an automated screening process on the original so called master source lists (MASOL), have been used to remove confused sources and 124 observations with too crowded regions and regions of high surface brightness diffuse emission. The resulting 50,408 sources have a likelihood of at least 10, corresponding to a rate of accidental detections of about 1 percent. This data base contains 80% of all PSPC observations. Since the acceptance criteria were rather conservative a total number of about 70,000 X-ray sources detected during the pointed PSPC observation phase can be expected.

The new catalogue has been moved into the public area and can be accessed via the interactive account xray (see header).

INTERACTIVE ACCOUNT XRAY

In the ROSAT Service Area we have now installed a copy of the HEASARC database system (developed by GSFC) including the BROWSE interface. Via the telnet address (given in the header) users can interactively access a large number of astronomical catalogs, and with the help of BROWSE select, correlate, extract and display data on sources and observations from missions like ROSAT, EINSTEIN, EXOSAT, GRO etc..

The new ROSAT PSPC Source Catalog is available under the database name rosatsrc (ROSAT sources), database rosatseq contains information on the individual observation fields. The command dbhelp within BROWSE will display general info on the catalog including explanations of the applied source selection and completeness criteria (available within the next 2 weeks).

EXSAS FOR LINUX

It is now possible to run EXSAS/MIDAS also on your PC under LINUX. The disk space used by both MIDAS and EXSAS (only executables are distributed) is in the order of 30 MBytes only. On systems with 486 processors of 50 MHz or more it runs similarly fast as on normal workstations. At the time of writing the first tests with the system run successfully. A (compressed) tar file of the LINUX version will be made available in the ROSAT Service Area within the next days, if further tests indicate no major problems.
Interested users that use already EXSAS (and therefore have the allowance to access the secured area) may then directly ftp the file named exsas/94JUL_EXP/94JUL_LINUX.tar.Z. Others users are asked to first fill in the EXSAS questionnaire that can be copied as exsas/questionnaire.form via the anonymous ftp account, and send it to us.
====================== end of ROSAT NEWS ================================ 
The ASCII version of the ROSAT source catalog contains the same information as
provided by the ROSATSRC data base in BROWSE.
The columns are:

SEQUENCE      ROSAT observation sequence number
ML_INDEX      MASOL main running number
NAME          ROSAT source name.
RA            Source right ascension HMS (equinox 2000)
DEC           Source declination DMS (equinox 2000)
RA            Source right ascension decimal degree (equinox 2000)
DEC           Source declination decimal degree (equinox 2000)
LII           Source galactic longitude
BII           Source galactic lattitude
ERROR_ML      Positional accuracy: error radius of Maximum Likelihood algorithm (arcsec)
ERROR_BOR     Positional accuracy: boresight error
ERROR_SYS     Positional accuracy: systematic error
ERROR_RADIUS  Positional accuracy: total error
OFFAXIS       Off-axis radius in arcmin
COUNT_RATE    Source counts per second (vignetting corrected)
COUNT_RATE_ERROR   Error on countrate
BACKGROUND    Background counts/sec/square arcmin
EXPOSURE      Exposure time in seconds (vignetting corrected)
HARDNESS1     Hardness ratio 1. Defined as (B-A)/(B+A).
HARDNESS1_ERROR    Error on hardness1.
HARDNESS2     Hardness ratio 2. Defined as (D-C)/(D+C).
HARDNESS2_ERROR    Error on hardness2.
EXTENT        Extent size in arcsec.
EXTENTLIK     Extent likelihood.
ML_LIKE       Likelihood from maximum-likelihood method
MD_LIKE       Likelihood of M-Detect algorithm.
RIBDIST       Distance to next rib or edge in arcsec
SRCDIST       Distance to next source in arcsec before screening
SRCCDIST      Distance to next source in arcsec after screening
PRIORITY      Source detection string. Each character describes the 
              detection/non-detection in each of the different energy bands:
               detection flag in MDetect broad band
               detection flag in LDetect broad band
               detection flag in MDetect hard band
               detection flag in LDetect hard band
               detection flag in MDetect soft band
               detection flag in LDetect soft band
               detection flag (broad=b,....)
CELL          Detect cell size.
VIGNETTING    Vignetting correction factor.
CONFUSION     Confusion indicator.
Differences in the two ROSAT catalogs of pointed PSPC observations Haberl F., Pietsch W., and Voges W. Max-Planck-Institut fuer extraterrestrische Physik We have compared the two catalogs of ROSAT sources (ROSATSRC, Voges W., Gruber R., Haberl F., Kuerster M., Pietsch W., and Zimmermann U., ROSAT NEWS No. 32; and WGACAT, White N.E., Giommi P., and Angelini L., IAU Circular 6100) and find differences with respect to Source positions, Source distribution at different off-axis angles, Detector vignetting, and Count rates. This study was not done in depth yet, and should not be considered as being complete, but the first results are so important in our view, that we want to bring it to the attention of the ROSAT community at this early stage. We are continuing this work and will update this information when available. A short summary of the results is given in the following: Source positions The WGACAT and ROSATSRC catalogs have been correlated with SIMBAD stars which have a position accuracy of better than 1.5 arcsec. For the ROSATSRC catalog 68% of the matching sources are found within 17 arcsec to the SIMBAD position (Fig. 1) In Fig. 1 one can even resolve the two peaks in declination separated by about 20 arcsec. This is caused by the boresight correction which was wrong by about 10 arcsec in the first processed revision 0 data. It also leads to a slight broadening of the distribution in right ascension. The improved boresight values used in revision 1 moves the peaks closer together (residual boresight error less than about 5 arcsec) and the source catalog can be used to further improve the boresight correction. Fig. 1a and 2a show the same correlation for sources in the inner part of the detector (within 19 arcmin off-axis angle) and Fig. 1b and 2b for the outer part. The distribution of distances to SIMBAD sources found for the WGACAT shows a systematic shift of about 5 arcsec in RA and about 15 arcsec in DEC. Moreover the distribution is asymmetric (Fig. 2). From an inspection of several images with plotted source positions (we used the FITS data from the archive and standard EXSAS procedures for creating images and overlaying the source positions) from both catalogs the shift between the source positions is visible by eye and is always in the same direction in the image (Fig. 3 and 4). The shift is larger in the outer part of the image where the images for the WGACAT have larger image binning. In the description of the WGACAT similar images and overlays of the same ROSAT pointing are presented. There are no systematic offsets between sources in the image and the overlay. This suggests an intrinsic problem connected to the relation between ROSAT image pixel and sky position in the XIMAGE package. Source distribution at different off-axis angles The number of sources found at different off-axis angles is very different in the WGACAT and ROSATSRC catalogs. While in the inner part of the detector the maximum-likelihood method used in the ROSATSRC is more sensitive and finds more sources than the sliding window method in the WGACAT, the number of sources in the WGACAT shows a strong peak between 16 and 20 arcmin (Fig. 5 and 6). For the WGACAT the images were split into two parts; the inner part inside 19 arcmin and the outer part outside 18 arcmin off-axis angle. The expected double identification due to the 1 arcmin overlap can not be responsible for the whole peak and the nature of the additional sources is not clear. The peak and a higher number of sources outside 22 arcmin, present in the WGACAT, are very prominent for source count rates below 0.04 cts/s (Fig. 7 and 8) while absent for count rates above 0.04 cts/s (Fig. 9 and 10). Also the distribution of sources which are common to both catalogs does not show the increased number of weak and spurious sources around the support ring (Fig. 11), indicating that a considerably higher number of weak sources is contained in the WGACAT between about 16 and 40 arcmin off-axis angle. (The absolute numbers in Fig. 11 are higher as they contain also multiple matches.) Detector vignetting The vignetting correction for the ROSATSRC sources is calculated per photon and then averaged. In the inner part of the detector where ML was running, this is done also energy dependent. Fig. 12 shows the vignetting correction as function of off-axis angle. For the WGACAT the vignetting correction is determined from the position of the source only and therefore shows no scatter. The vignetting correction in the WGACAT is energy independent and lies below the values derived from the official effective area calibration file. The difference increases with off-axis angle and is about 2% at 10 arcmin up to about 10% at 50 arcmin, and is even larger for hard sources. Count rates In the outer part of the detector the count rates in the ROSATSRC catalog are not corrected for the point spread function and give only the counts inside the cut radius, corrected for vignetting. Therefore the count rates can be significantly too low and cases were found with a factor of two discrepancy. Further investigations in this direction are in progress. Postscript files of figures: Fig. 1: mpe_simbad.ps.gz Fig. 2: wga_simbad.ps.gz Fig. 1a: mpe_simbad_in.ps.gz Fig. 2a: wga_simbad_in.ps.gz Fig. 1b: mpe_simbad_out.ps.gz Fig. 2b: wga_simbad_out.ps.gz Fig. 3: us200008_full.ps.gz Fig. 4: us200008_in.ps.gz The Pleiades Center pointing also shown in the WGA catalog description; the crosses denote the ROSATSRC positions, the circles the WGACAT positions from the inner part images and the squares the WGACAT positions from the outer part images Fig. 5: mpe_number_offaxis.ps.gz Fig. 6: wga_number_offaxis.ps.gz Fig. 7: mpe_weak_number_offaxis.ps.gz Fig. 8: wga_weak_number_offaxis.ps.gz Fig. 9: mpe_strong_number_offaxis.ps.gz Fig.10: wga_strong_number_offaxis.ps.gz Fig.11: wga_mpe_number_offaxis.ps.gz Fig.12: mpe_vign_offaxis.ps.gz ROSAT Status Report # 113 Dec 12 1994 Comments on the WGACAT/ROSATSRC Comparison Report by MPE N.E. White, L. Angelini and P. Giommi In the report from MPE on a comparison of the wgacat and rosatsrc catalogs (see below) they report several significant differences. Probably the most critical is an offset in the positions between wgacat and simbad. Investigation by us confirms there is a problem in the WGACAT positions, with a 6 arc sec offset in the inner region and 15 arc sec in the outer. These offsets are comparable to the quoted uncertainties in the ROSAT boresight, which is one reason we had not noticed it before. If you have been using the default 1 arc min search radius in browse, it is not likely to be a problem. We have traced the source of the error and a corrected catalog is being generated. We hope to have it released within the next 2-3 weeks. This will also contain additional sources from new fields that have recently entered the archive. Here is a rule of thumb to correct the positions. Its not a simple scaling and depends on whether the source is less than 7860,7860 in detector coords. If the X pixel coord is less than 7860 then to the RA ADD 4 arc sec in the inner region, and 10 arc sec in the outer (denoted by the source designation being _in or _out). If the y coord is less than 7860 SUBTRACT from the dec 4 arc sec and 10 arc sec if it is, respectively, in the inner or outer regions. In addition to this, there is a overall offset of order 5 arc sec in the outer region and 2 arc sec in the inner. These latter corrections should be applied in the sense. The other points mentioned are an excess of faint sources between 16 and 20 arc sec in wgacat. There is an overlap in the separate runs made for the inner and outer regions, close to the inner rib. In the overlap region the source detect for the outer region is more sensitive due to an overall lower background. We would recommend that all _out sources within OFFSET < 19 arc sec be treated with caution. The differences in the vignetting are much as expected, since we used a simple approximation. On the other side, the ROSATSRC count rates in the outer region are wrong because they did not include the psf correction.