This conference presentation was prepared for the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation, 2022.
We designed and built a laboratory model of a sparse space telescope. The purpose of the model is to test various algorithmic, optical, and mechanical issues with such a telescope: how to achieve alignment after deployment that yields diffraction limited optical performance. Our model uses four non-redundant sparse sectors. Each segment has three degrees of freedom, with supplementary coarse focusing, so the search volume for a perfect image is quite large, ~1051. We tried stochastic searches, optimizing the point spread to its minimum, and are now testing different directed search algorithms, of volume order 1019 or less. This will cut the search time from one day to about one hour, with much less chance of actuator failure.
The XRISM X-ray observatory will fly two advanced instruments, the Resolve high-resolution spectrometer and the Xtend wide-field imager. These instruments, particularly Resolve, pose calibration challenges due to the unprecedented combination of spectral resolution, spectral coverage, and effective area, combined with a need to characterize the imaging fidelity of the full instrument system to realize the mission’s ambitious science goals. We present the status of the XRISM in-flight calibration plan, building on lessons from Hitomi and other X-ray missions. We present a discussion of targets and observing strategies to address the needed calibration measurements, with a focus on developing methodologies to plan a thorough and flexible calibration campaign and provide insight on calibration systematic error. We also discuss observations that exploit Resolve’s spectral
The X-Ray Imaging and Spectroscopy Mission (XRISM) is the successor to the 2016 Hitomi mission that ended prematurely. Like Hitomi, the primary science goals are to examine astrophysical problems with precise highresolution X-ray spectroscopy. XRISM promises to discover new horizons in X-ray astronomy. XRISM carries a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly and a co-aligned X-ray CCD camera that covers the same energy band over a large field of view. XRISM utilizes Hitomi heritage, but all designs were reviewed. The attitude and orbit control system were improved in hardware and software. The number of star sensors were increased from two to three to improve coverage and robustness in onboard attitude determination and to obtain a wider field of view sun sensor. The fault detection, isolation, and reconfiguration (FDIR) system was carefully examined and reconfigured. Together with a planned increase of ground support stations, the survivability of the spacecraft is significantly improved.
The detection of astrophysical Gamma-Ray Bursts (GRBs) has always been intertwined with the challenge of identifying the direction of the source. Accurate angular localization of better than a degree has been achieved to date only with heavy instruments on large satellites, and a limited field of view. The recent discovery of the association of GRBs with neutron star mergers gives new motivation for observing the entire γ-ray sky at once with high sensitivity and accurate directional capability. We present a novel γ-ray detector concept, which utilizes the mutual occultation between many small scintillators to reconstruct the GRB direction. We built an instrument with 90 (9 mm)3 CsI(Tl) scintillator cubes attached to silicon photomultipliers. Our laboratory prototype tested with a 60 keV source demonstrates an angular accuracy of a few degrees for ∼25 ph cm−2 bursts. Simulations of realistic GRBs and background show that the achievable angular localization accuracy with a similar instrument occupying 1l volume is < 2° . The proposed concept can be easily scaled to fit into small satellites, as well as large missions.
ISS-TAO is a mission selected for a concept study by NASA, and proposed by GSFC for launch to the International Space Station (ISS) in order to observe transient high-energy astrophysical sources. It is composed of an X-ray Wide-Field Imager (WFI), and a multi-directional Gamma-ray Transient Monitor (GTM). WFI will be built by NASA/GSFC while the secondary GTM, described in this article is contributed by the Israel Space Agency (ISA) and developed at the Technion, Israel Institute of Technology, in collaboration with Israel space industries. ISS-TAO's main science goal is to detect electromagnetic (EM) counterparts to gravitational waves (GW) detected by GW observatories, such as the Laser Interferometer GW Observatory (LIGO). Observations of simultaneous GW and EM counterparts will address fundamental questions on the nature of coalescing neutron stars and black holes as astrophysical GW sources. An EM detection will also increase LIGO’s sensitivity to detecting these events above the GW background. Promising candidates for LIGO GW sources and EM counterparts are coalescing neutron star binaries, which are now known to also emit a short Gamma-Ray Burst (sGRB). The GTM will measure these GRBs and other transient gamma-ray events, and will trigger the WFI, with or without a GW trigger. The concept of the GTM detector consists of a compact configuration of 4 segments, which will allow a fair angular resolution of a few hundred square degrees, which will facilitate a prompt follow up. Each of the GTM segments consists of a crystal scintillator, a photo-multiplier tube (PMT), followed by analog and digital electronics designed to reconstruct the energy of each incoming photon, and to yield the light-curve and spectrum of any gamma-ray transient. A central CPU then calculates the ratio of the signal of each one of the segments, and deduced the transient position relative to the GTM.
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