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The WGA Catalog of ROSAT Sources
The large field of view of the ROSAT PSPC made it an ideal instrument to
find a large number of serendipitous X-ray sources. WGACAT is a catalog
generated from all the ROSAT PSPC pointed observations available in the
HEASARC public archive. The catalog resulted from an independent research
effort by HEASARC staff (White and Angelini) and BeppoSAX Science Data
Center staff (Giommi) with the aim of creating a catalog of sources
detected by ROSAT in its pointed phase. The goals were to: 1) identify the
detected sources, 2) ensure their timely observation by currently active
X-ray missions e.g., ASCA, BeppoSAX and RXTE, 3) to search for objects
which show exceptional time variability and spectral properties, and 4) to
provide an independent check of the detection technique used in the
official ROSAT project (SASS) processing. The catalog was created using
the source detection algorithm within XIMAGE on all the public ROSAT
PSPC pointed data available in the summer of 1994 (~70%) of the entire
set. A total of ~62,000 unique sources were listed in the first version of
WGACAT, made publicly available in November 1994 through the HEASARC
on-line service (White et al. 1994, BAAS 185, 41.11).
A comparison with the project-generated ROSAT catalog reveals that
WGACAT is much more sensitive in the outer area of the PSPC (where
much more sky coverage is contained) and slightly less sensitive in
the central regions. So the two catalogs are very complementary. In
the past year the remaining PSPC fields have been processed and an
updated version of the catalog will be released in May 2000. This
update also includes a comprehensive quality check of the validity of
the sources found. The updated WGACAT contains 88,000 sources and was
made possible thanks to an ADP grant awarded in 1998. The ultimate aim
of this project (ADP PI L. Angelini) is to provide a unified
object-based catalog of X-ray sources (called XCAT) that merges all
the ROSAT, EXOSAT, ASCA and Einstein catalogs.
The richness of WGACAT has stimulated many research projects and
resulted in more than 40 papers in the Ap J. Singh et al. (1995, ApJ
455, 456) identified a sample of very soft X-ray sources that included
white dwarfs, cataclysmic variables (Szkody et al. 1995, ApJ 455,
L43), stars and a group of sources that are probably Seyferts I with a
very step spectrum (Singh & Laurence 2000, MNRAS 312, 308).
Israel et al. (1997, ApJ 484, L141; 1997, ApJ 474, L53;
1998, MNRAS 298, 502) discovered a number of X-ray pulsators by
searching the WGACAT lightcurves. Fiore et al. (1998, ApJ
492, 79), Elvis et al. (1998, ApJ 492, 91), and Padovani et al. (1997,
MNRAS, 286, 415) used WGACAT to shown: 1) radio-loud quasars commonly
exhibit low-energy X-ray cutoffs that increase with
redshift rather than with luminosity, indicating evolution with cosmic
epoch, and 2) X-ray emission of the flat-spectrum radio quasars
and BL Lacs is generated by the same mechanism but occurs in radio
galaxies of lower power.
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Last modified: Monday, 19-Jun-2006 11:24:57 EDT
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