An X-ray Calorimeter on the Spectrum-X Gamma Mission
Randall Smith (JHU & NASA/GSFC)
The Russian Spectrum-X-Gamma (SXG) Mission is now under development to carry out the first moderate-resolution, all-sky survey of the x-ray sky since ROSAT. This mission shares the name of the original SXG developed in the 1980s (and not launched due to budget problems) but has been completely redesigned. SXG is a medium-sized satellite ( 2200 kg) to be launched in 2011/12 into a 600 km equatorial (<5 deg) orbit from Kourou or into a <30 deg orbit from Baikonur as a fallback option. The payload includes eROSITA (extended ROentgen Survey with an Imaging Telescope Array, MPE, Germany) with 7 Wolter-type telescopes, the wide field X-ray monitor Lobster (LU, UK), the X-ray concentrator based on Kumakhov optics ART or coded-mask X-ray telescopes as a fallback (IKI, Russia) and GRB detector (Russian consortium). The mission will conduct the first all-sky survey with an imaging telescope in the 2-12 keV band to discover the hidden population of several hundred thousand obscured supermassive black holes and the first all-sky imaging x-ray time-variability survey. It will observe the extragalactic sky with high enough sensitivity to detect 50,000-100,000 clusters of galaxies for follow-up pointed observations of selected sources to provide a rich new data set for probing dark matter and dark energy. The survey will also provide valuable data on point sources, populations of unresolved sources that make up galactic diffuse emission along the plane, and diffuse emission from hot gas. SXG will also include an x-ray calorimeter spectrometer developed by NASA/GSFC to provide grating-level spectral resolution, recovering part of the science that was lost from the untimely demise of the Suzaku/XRS. The design will incorporate a 1.6 m f/l x-ray telescope (an copy of one of the eROSITA units) coupled to a spare x-ray calorimeter from the XRS program. Operating in a dewar designed and built in Japan, we expect a resolution of 4 eV (FWHM) at 6 keV. The dewar would be based on flight-heritage cryocoolers and cable of long life without cryogens. With this instrument, the long-standing puzzles of the Galactic x-ray emission would finally be addressed with high spectral resolution and better than 2 arcmin spatial resolution over the entire sky. This would create the best chance ever for disentangling and physically identifying the numerous Galactic components responsible for the diffuse x-ray emission. In addition, the instrument could be used for pointed-mode observations (e.g early in the mission and at the completion of the surveys), thereby creating the possibility of a sampling of scientific topics that were planned for the original Suzaku program.