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ROSAT Status Report #107

                     ROSAT Status Report #107
                           Oct 31, 1994

This bulletin describes the release of two ROSAT catalogs derived from 
archival data taken during the pointed phase. One is from the ROSAT
data center and is derived from the results of the SAS processing. The
other has been produced indepently by White (HEASARC), Giommi (ESIS) and 
Angelini (HEASARC) as their own research effort. These catalogs have 
approximately 50,000 sources, by far the largest X-ray catalogs in existance
and represent a major new resource for the astronomical community. Since
the two catalogs have been produced independently from the same archival 
data, they can be used as a quality crosscheck.

                   ROSAT WGACAT Point Source Catalog 

A ROSAT catalog of point sources called WGACAT is now available through the
HEASARC online service. This catalog has been generated by N.E.White
(HEASARC/GSFC), P. Giommi (ESIS/ESA) and L. Angelini (HEASARC/GSFC) using the
ROSAT PSPC pointed data publically available up to Sept 1994. This catalog,
which contains 50,000 detections and more than 45,600 individual sources. A
total of 2624 fields were searched. This catalog is an independent research
effort aimed at releasing as quickly as possible a list of sources detected
by ROSAT in its pointed phase to: 1) identify the detected sources, 2) 
ensure their timely observation by currently active X-ray missions e.g. ASCA,
and 3) to search for objects which show exceptional time variability and
spectral properties. Papers on the WGACAT will be presented this week at the
AAS/HEAD meeting, and also at the AAS meeting in Tucson in January. A
preliminary paper was presented at the ADASS meeting in Baltimore several
weeks ago.

WGACAT was generated using the optimized sliding cell detect in XIMAGE (first
developed for the EXOSAT project). The inner and outer parts of the images
were run separately, to maximize the source detection sensitivity. This method
is an excellent approach for finding point sources, but can also find spurious
sources where there is extended emission. A visual quality check on the detect
output has been made and obvious problem fields and sources flagged. Users of
this catalog should carefully check the QFLAG parameter for each source
(values >5 are good and are the ones provided by default) and examine the gif
images that have been provided. WGACAT has been cross-correlated against many
other catalogs and the results written to the catalog. GIF and FITS format
images of the image of each detected source, its lightcurve and spectrum
will be made available (within the next week).

WGACAT can be accessed via the HEASARC online service by logging into
legacy.gsfc.nasa.gov with the username xray. Type "browse wgacat" to access
the catalog. For information on the catalog contents type dbhelp from the
Browse command line. The commmands sc, simbad, sn, and sp can be used to
search the catalog. Contact request@legacy.gsfc.nasa.gov to receive a Browse
users guide. 

Alternately WGACAT can be accessed via the HEASARC WWW Browse interface under
http://heasarc.gsfc.nasa.gov/StarTrax/Browse.html by clicking on ROSAT and
then selecting WGACAT. 

Send mail to wgacat@athena.gsfc.nasa.gov if you have any questions regarding 
this catalog. 

N.E. White, P. Giommi and L. Angelini (30 Oct 1994)

=                                                                       =
=              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          =
=   WFC Archive access via telnet/ftp ait.physik.uni-tuebingen.de       =
=                                user: xuv  (password: xuv_archive)     =

          - EXSAS FOR LINUX

No major problems were encountered during the last month. 

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.

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 
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).

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). 

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 ================================