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  • 1
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    Monte-Carlo Estimation of the Inflight Performance of the GEMS Satellite X-Ray Polarimeter (2014)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We report a Monte-Carlo estimation of the in-orbit performance of a cosmic X-ray polarimeter designed to be installed on the focal plane of a small satellite. The simulation uses GEANT for the transport of photons and energetic particles and results from Magboltz for the transport of secondary electrons in the detector gas. We validated the simulation by comparing spectra and modulation curves with actual data taken with radioactive sources and an X-ray generator. We also estimated the in-orbit background induced by cosmic radiation in low Earth orbit.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN28527 , SPIE Digital Library; 9144
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    NASA TECHNICAL REPORTS
  • 2
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    Performance Verification of the Gravity and Extreme Magnetism Small Explorer GEMS X-Ray Polarimeter (2014)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: olarimetry is a powerful tool for astrophysical observations that has yet to be exploited in the X-ray band. For satellite-borne and sounding rocket experiments, we have developed a photoelectric gas polarimeter to measure X-ray polarization in the 2-10 keV range utilizing a time projection chamber (TPC) and advanced micro-pattern gas electron multiplier (GEM) techniques. We carried out performance verification of a flight equivalent unit (1/4 model) which was planned to be launched on the NASA Gravity and Extreme Magnetism Small Explorer (GEMS) satellite. The test was performed at Brookhaven National Laboratory, National Synchrotron Light Source (NSLS) facility in April 2013. The polarimeter was irradiated with linearly-polarized monochromatic X-rays between 2.3 and 10.0 keV and scanned with a collimated beam at 5 different detector positions. After a systematic investigation of the detector response, a modulation factor greater than or equal to 35% above 4 keV was obtained with the expected polarization angle. At energies below 4 keV where the photoelectron track becomes short, diffusion in the region between the GEM and readout strips leaves an asymmetric photoelectron image. A correction method retrieves an expected modulation angle, and the expected modulation factor, approximately 20% at 2.7 keV. Folding the measured values of modulation through an instrument model gives sensitivity, parameterized by minimum detectable polarization (MDP), nearly identical to that assumed at the preliminary design review (PDR).
    Keywords: Astrophysics; Instrumentation and Photography
    Type: GSFC-E-DAA-TN28520 , Proceedings of SPIE (ISSN 0277-786X); 9144; 91444M-91444M-12
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    NASA TECHNICAL REPORTS
  • 3
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    Properties of the Flight Model Gas Electron Multiplier for the GEMS Mission (2014)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present the gain properties of the gas electron multiplier (GEM) foil in pure dimethyl ether (DME) at 190 Torr. The GEM is one of the micro pattern gas detectors and it is adopted as a key part of the X-ray polarimeter for the GEMS mission. The X-ray polarimeter is a time projection chamber operating in pure DME gas at 190 Torr. We describe experimental results of (1) the maximum gain the GEM can achieve without any discharges, (2) the linearity of the energy scale for the GEM operation, and (3) the two-dimensional gain variation of the active area. First, our experiment with 6.4 keV X-ray irradiation of the whole GEM area demonstrates that the maximum effective gain is 2 x 10(exp 4) with the applied voltage of 580 V. Second, the measured energy scale is linear among three energies of 4.5, 6.4, and 8.0 keV. Third, the two-dimensional gain mapping test derives the standard deviation of the gain variability of 7% across the active area.
    Keywords: Instrumentation and Photography
    Type: GSFC-E-DAA-TN28531 , SPIE Astronomical Telescopes + Instrumentation 2014; Jun 22, 2014 - Jun 27, 2014; Montreal, Quebec; Canada|Proceedings of SPIE; 9144; 91444N|Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray; Jun 22, 2014 - Jun 27, 2014; Montreal, Quebec; Canada
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    NASA TECHNICAL REPORTS
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