The Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket is a sounding rocket experiment
combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to
obtain high- spectral-resolution images of extended X-ray sources. The target for Micro-X’s first
flight (slated for January
2013) is the Puppis A supernova remnant. The Micro-X observation of the bright eastern knot of
Puppis A will obtain a line-dominated spectrum with up to 27,000 counts collected in 300 seconds at
2 eV resolution across the 0.3-2.5 keV band. Micro-X will determine the thermodynamic and
ionization state of the plasma, search for line shifts and broadening associated with dynamical
processes, and seek evidence of ejecta enhancement. We describe the progress made in developing
this payload, including the detector, cryogenics, and electronics
Micro-X is a rocket-borne X-ray telescope which will use an array of Transition Edge Sensor (TES) microcalorimeters
to obtain high resolution soft X-ray spectra of extended astronomical sources. The microcalorimeter array consists of
128 pixels with a size of 590 μm × 590 μm each. The TESs are read out with a time-division Superconducting Quantum
Interference Device (SQUID) multiplexing system. The instrument's front end assembly, which contains the
microcalorimeter array and two SQUID amplification stages, is located at the focal point of a conically approximated
Wolter mirror with a focal length of 2100 mm and a point spread function of 2.4 arcmin half-power diameter. The
telescope's effective area amounts to ~ 300 cm2 at 1 keV. The TES array is cooled with an Adiabatic Demagnetization
Refrigerator. The first flight of Micro-X is scheduled for 2011, and will likely target a Si knot in the Puppis A supernova
remnant. The time available for the observation above an altitude of 160 km will be in excess of 300 seconds. The
design, manufacturing and assembly of the flight hardware has recently been completed, and system testing is underway.
We describe the final design of the Micro-X instrument, and report on the overall status of the project.
The Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket is sounding rocket experiment that will combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to obtain high-spectral-resolution images of extended and point X-ray sources. Our first target is the Puppis A supernova remnant, which will be observed in January 2011. The Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with up to 90,000 counts collected in 300 seconds at 2 eV resolution across the 0.3-2.5 keV band. Micro-X will utilize plasma diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. We describe the progress made in developing this payload, including the detector, cryogenics, and electronics assemblies. A detailed modeling effort has been undertaken to design a rocket-bourne adiabatic demagnetization refrigerator with sufficient magnetic shielding to allow stable operation of transition edge sensors, and the associated rocket electronics have been prototyped and tested.
Micro-X is a proposed sounding rocket experiment that will combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to obtain high-spectral-resolution images of extended and point X-ray sources. We describe the payload and the science targeted by this mission including the discussion of three possible Micro- X targets: the Puppis A supernova remnant, the Virgo Cluster, and Circinus X-1. For example, a Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with 90,000 counts collected in 300 seconds at 2 eV resolution across the 0.3-2.5 keV band. Micro-X will utilize plama diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. For clusters of galaxies, Micro-X can uniquely study turbulence and the temperature distribution function. For binaries, Micro-X's high resolution spectra will separate the different processes contributing to the Fe K lines at 6 keV and give a clear view of the geometry of the gas flows and circumstellar gas.
We report on our studies of possible configurations for the focal plane of the Constellation-X mission. Taking
advantage of new developments in both SQUID multiplexing technology and position-sensitive detectors, we
present a viable focal plane intrument design that would greatly enhance the reference Constellation-X configuration
of a 32 × 32 array. An order of magnitude increase in the number of pixels of the focal plane array from
the current 1024-pixel reference design is achievable.
We have been developing x-ray microcalorimeters for the Constellation-X mission. Devices based on superconducting transition-edge sensors (TES) have demonstrated the potential to meet the Constellation-X requirements for spectral resolution, speed, and array scale (> 1000 pixels) in a close-packed geometry. In our part of the GSFC/NIST collaboration on this technology development, we have been concentrating on the fabrication of arrays of pixels suitable for the Constellation-X reference configuration. We have fabricated 8x8 arrays with 0.25-mm pixels arranged with 92% fill factor. The pixels are based on Mo/Au TES and Bi/Cu or Au/Bi absorbers. We have achieved a resolution of 4.0 eV FWHM at 6 keV in such devices, which meets the Constellation-X resolution requirement at 6 keV. Studies of the thermal transport in our Bi/Cu absorbers have shown that, while there is room for improvement, for 0.25-mm pixels the standard absorber design is adequate to avoid unacceptable line-broadening from position dependence caused by thermal diffusion. In order to improve reproducibility and to push closer to the 2-eV goal at 6 keV, however, we are refining the design of the TES and the interface to the absorber. Recent efforts to introduce a barrier layer between the Bi and the Mo/Au to avoid variable interface chemistry and thus improve the reproducibility of device characteristics have thus far yielded unsatisfactory results. However, we have developed a new set of absorber designs with contacts to the TES engineered to allow contact only in regions that do not serve as the active thermometer. We have further constrained the design so that a low-resistance absorber will not electrically short the TES. It is with such a design that we have achieved 4.0 eV resolution at 6 keV.
We have investigated the thermal, electrical, and structural properties of Bi and BiCu films that are being developed as X-ray absorbers for transition-edge sensor (TES) microcalorimeter arrays for imaging X-ray spectroscopy. Bi could be an ideal material for an X-ray absorber due to its high X-ray stopping power and low specific heat capacity, but it has a low thermal conductivity, which can result in position dependence of the pulses in the absorber. In order to improve the thermal conductivity, we added Cu layers in between the Bi layers. We measured electrical and thermal conductivities of the films around 0.1 K, the operating temperature of the TES calorimeter, to examine the films and to determine the optimal thickness of the Cu layer. From the electrical conductivity measurements, we found that the Cu is more resistive on the Bi than on a Si substrate. Together with a SEM picture of the Bi surface, we concluded that the rough surface of the Bi film makes the Cu layer resistive when the Cu layer is not thick enough to fill in the roughness. From the thermal conductivity measurements, we determined the thermal diffusion constant to be 2 x 103 μm2μs-1 in a film that consists of 2.25 μm of Bi and 0.1 μm of Cu. We measured the position dependence in the film and found that its thermal diffusion constant is too low to get good energy resolution, because of the resistive Cu layer and/or possibly a very high heat capacity of our Bi films. We show plans to improve the thermal diffusion constant in our BiCu absorber.
Over the last year a GEANT model of the Astro-E2 XRS instrument (including the surrounding structure of the telescope) has been developed in order to determine the rate and energy spectrum of background events due to cosmic ray protons. Background events, in the x-ray signal energy band, can be caused by the primary protons themselves, secondaries which are created in the material surrounding the XRS, or by decays of nearby activated materials. This paper will present the details of the GEANT model and will discuss the effectiveness of the telescope structure in shielding the XRS instrument and efficiency of the anti-coincidence detector at further reducing the background rate. We will also present an investigation of the rate and spectrum of cosmic ray particles passing through the Si frame, which acts as a mechanical support and thermal sink to the x-ray pixels, in order to determine whether sufficient heating will occur in the Si frame to affect the response of the x-ray pixels.
We present our latest results from our development of Position-Sensitive Transition-Edge Sensors (PoSTs). Our devices work as one-dimensional imaging spectrometers. They consist of a long absorber (segmented or solid) with a transition-edge sensor (TES) on each end. When X-rays hit the absorber, the comparison of the signals sensed in the two TESs determine the position of the TES, while the addition of the signals gives the energy of the X-ray. We obtained impedance curves for three different devices and obtained reasonable fits with our theoretical PoST model.