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P.J. Green, B.J. Wilkes, E.J. Hooper, A. Vikhlinin, H. Tananbaum (Harvard-Smithsonian CfA), S. Mathur (OSU), C.B. Foltz (MMTO), ChaMP Collaboration
With the successful launch and operation of NASA's Chandra X-ray Observatory (CXO, formerly AXAF), the Chandra Multiwavelength Project (ChaMP) will study Chandra serendipitous X-ray sources from radio to X-rays, with an optical survey as its backbone.
Important scientific advances, many unanticipated, have resulted from optical identification of serendipitous X-ray sources. Great challenges have faced such campaigns because of the large (~1') X-ray positional uncertainties. By contrast, Chandra's ~1\arcsec astrometry and tight PSF (\leq 1\arcsec on axis, ~10\arcsec even 8\arcmin off-axis) enable unambiguous identification of the optical counterparts in images well-matched in depth. Although ChaMP optical followup will exclude several targeted deep fields, thanks to Chandra's PSF and its extremely low background, sources as faint as f(0.2-8{\rm keV})~\times10-16 erg cm-2 s-1 will be detected - about 20 times as deep as current wide-area surveys. At the same time, we expect ChaMP to cover larger areas (~7 degrees2 per year) than current deep surveys.
We describe the scientific motivation and observing strategies for ChaMP optical followup of selected high galactic latitude Chandra fields. The project, nominally lasting about 5 years, should identify about 2000 high galactic latitude serendipitous X-ray sources per year, of which as many as 80% may be AGN. The broader (0.2-8keV) spectral range of Chandra will detect a much larger fraction of obscured AGN than in previous large-scale X-ray-selected samples. Enhanced detection of extended X-ray emission should yield a sample of over 200 distant clusters of galaxies in the critical redshift range z~0.2-1, which will be used for studies of cosmology and cluster evolution.