"We propose to develop a revolutionary x-ray camera for astrophysical imaging spectroscopy. High-resolution x-ray spectroscopy is a powerful tool for studying the evolving universe. Emission line ratios (e.g. within the He-like triplet) provide density and temperature diagnostics. Emission and absorption line energies identify ions and determine their velocities, and the shape of the lines can be used to study turbulence or the relativistic effects of a supermassive black hole. The grating spectrometers on the XMM and Chandra satellites demonstrated the power of high-resolution x-ray spectroscopy for astrophysics, but there remains a need for instrumentation that can provide higher spectral resolution with high throughput in the Fe-K band and that can enable spatial/spectral investigations of extended sources, such as supernova remnants and galaxy clusters. The instrumentation needed is a broad-band imaging spectrometer - basically an x-ray camera that can precisely resolve x-ray energies and fluxes over a large field-of-view.

While we do not claim that in 3 years we will have developed such detectors, we advocate developing the technology that has the greatest potential for achieving this. Theoretically, magnetically-coupled microcalorimeters are best equipped to achieve sub-eV energy resolution in very large formats. We propose to build upon the work carried out by our group on metallic magnetic calorimeters (MMC) in the antecedent program. The great promise of MMCs for sub-eV energy resolution has been recognized for years. During our current research program, an accident in detector fabrication produced devices that derived their sensitivity from a different operating principle - the temperature dependence of a superconduc