4.2. Upcoming and Planned X-ray Missions
In the future, both large ( US $1 billion, or 600 billion Chilean pesos; see Figure 14) and small-to-medium class ( US $120-180 million) X-ray missions should substantially advance the AGN X-ray survey work described above. Constellation-X, for example, should enable high-quality X-ray spectroscopy for some of the remarkable brighter sources found in X-ray surveys. XEUS should be able to generate hundreds of fields that are as sensitive as the deepest Chandra surveys, while also providing superior photon statistics to those available presently. Fitting of high-quality XEUS spectra should allow direct redshift determination in many cases. Ultimately, Generation-X will reach flux limits ~ 100 times better than those of Chandra and XEUS (see Figure 14). This improved sensitivity should allow detection and study of ~ 1000 M "proto-quasars" at z 10-15, enabling investigation of how the stellar-mass black holes made by the deaths of the first stars grew to make the first AGN.
Figure 14. Flux limit from 0.5-2 keV versus faint-source positional accuracy for some past, present, and future X-ray missions (the locations in the diagram and launch dates for future missions are approximate). With a 5-10 Ms exposure, Chandra can achieve sensitivities comparable to those discussed for XEUS. Furthermore, Chandra positions are likely to be the best available for 15 yr. Also shown are the expected X-ray fluxes from (1) the black holes made by the deaths of the first stars at z ~ 15, and (2) proto-quasars containing black holes of mass ~ 103 - 104 M at z ~ 10-15.
Future small-to-medium class X-ray missions, at least one to be launched soon, will sensitively survey large areas of sky at high X-ray energies; some will access the poorly explored 10-200 keV band covering the peak of the XRB. After its 2004-2005 launch, for example, Swift will serendipitously conduct the most sensitive 10-150 keV survey to date with its Burst Alert Telescope. A large fraction of the sky should be covered over the lifetime of Swift, and 200-400 AGN should be detected. In the 2007-2010 timeframe, proposed missions such as the Dark Universe Observatory (DUO) and the Nuclear Spectroscopic Telescope Array (NuSTAR) will also hopefully conduct sensitive surveys in the 0.3-8 keV and 6-80 keV bands, respectively. DUO would detect ~ 160,000 AGN in its surveys of the North Galactic Cap (the SDSS area) and South Galactic Pole, while NuSTAR would carry the first highly sensitive, focusing telescope for > 10 keV X-rays. Other planned small-to-medium class missions include Japan's Monitor of All-sky X-ray Image (MAXI) and New X-ray Telescope (NeXT) as well as Europe's LOBSTER and ROSITA. The Black Hole Finder Probe, defined as part of NASA's Beyond Einstein program, should ultimately obtain an all-sky census of accreting black holes using a wide-field imaging telescope in the 10-600 keV band.
We gratefully acknowledge support from NSF CAREER award AST-9983783, CXC grant GO2-3187A, the Royal Society (DMA), the PPARC (FEB), and Italian Space Agency contract ASI/I/R/057/02 (CV). We thank all of our collaborators.