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Goddard Space
Flight Center NASA > GSFC > Astrophysics Science Division > IXO |
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The X-ray Microcalorimeter Spectrometer (XMS) on IXO combines high spectral resolving power in a large array to provide non-dispersive imaging spectroscopy over a broad energy range. The driving performance requirements are to provide spectral resolution of 2.5 eV over the central 2 × 2 arcmin in the 0.3–7.0 keV band, and 10 eV over the entire 5 × 5 arcmin field of view. See Requirements.
XMS spectroscopic capability will provide extraordinary sensitivity to absorption features, via iron Kα and many other metal species, and will be uniquely powerful at revealing conditions in the immediate vicinity of the Supermassive Black Holes (SMBH), including black-hole driven winds. Detection of powerful winds in Active Galactic Nucleus (AGN) hosts at the major epoch of galaxy formation is the "smoking gun" of feedback, and detailed spectroscopy will reveal the velocity, column density, metallicity and ionization structure of the outflows for detailed comparison with physical models, which are at present completely unconstrained. See Science Goals - Cosmic Feedback.
Thermodynamics limits determine the spectral resolution and drive the need for operation at a temperature below ˜0.05 K. Although extraordinarily cold, such temperatures can be readily achieved and maintained using flight-proven techniques.
IXO has an international team of technology development in the US, Japan and Europe, all working on the development of microcalorimeter systems.
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1. XMS - side view + Larger Version |
2. XMS - back view + Larger Version |
3. XMS - cutaway view + Larger Version |
Photograph of a TES array and low-temperature read-out components. An 8×8 Goddard TES array is embedded in a 4-column NIST time-division multiplexer testbed. This testbed was used for demonstrating simultaneous read out of 16 TES channels, each with better than 3 eV resolution, using only two amplifier chains. Click the image for larger view.
One candidate technology under development for IXO is superconducting transition-edge sensor (TES) microcalorimeters. TES microcalorimeters are operated in the narrow temperature range between the onset of non-zero resistance and the fully normal state. The change in resistance is measured by monitoring the current through a voltage-biased TES using a superconducting quantum interference device (SQUID).
Imaging TES detectors will have at least four imaging elements connected to one TES through links with different thermal conductances. Position information will be obtained from analysis of the pulse shapes.
For more information, refer to
Multiplexed readout of uniform arrays of TES X-ray, Caroline Kilbourne et al., SPIE 2008
Photo of technology demonstration Continuous Adiabatic Demagnetization Refrigerator under development at NASA's Goddard Space Flight Center.
The microcalorimeter will require a cooling system such as the Continuous Adiabatic Demagnetization Refrigerator (CADR) and cryocooler. This system has the advantage of having no stored cryogens, thus maximizing the lifetime/mass ratio for the instrument.
Cooling of the detector stage will be achieved using a multistage CADR, which provides the necessary cooling power down to 50 mK. The warmer stages of the CADR are sequentially linked through heat switches and then cycled to transfer heat to the relatively warm cryocooler interface. A mechanical cryocooler will provide the <5 K heat sink for the CADR and will actively cool several thermal shields within the cryostat.
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