Robin L. Shelton

XBSS: the X-Ray Background Spectroscopic Survey

The x-ray background spectroscopic survey (XBSS) is a SMEX mission proposed to perform a high spectral resolution all-sky survey of diffuse x-ray emission in the 50 - 2000 eV range. This spectral exploration of the x-ray background with high energy resolution will resolve important questions about the role of hot gas in the structure and evolution of the interstellar medium, the Galactic halo, and nearby intergalactic space that cannot be answered in any other way. The temperature distribution, emission measure, ionization distribution, and metallicity of the gases responsible for this emission are unknown. The survey is performed with a 6 by 6 array of cryogenic microcalorimeters that have spectral resolution of approximately 4 eV FWHM. The satellite is spin- stabilized with the spin axis directed toward the sun. The detectors look 90 degrees to the spin axis with a mechanically collimated field of view that is 5 degrees in radius. The instrument scans the entire sky twice in twelve months. During the second survey, deep exposures are performed along selected ecliptic meridians with the span axis fixed for up to 20 days at a time.