Providing a Special Thermal Environment of the ART-XC Reflecting X-ray Telescope as a Necessary Condition for Obtaining Significant Scientific Results

The X-ray Telescope (XRT) aboard Hinode was designed to observe the solar corona in its entire temperature range, spanning from below 1 million Kelvin (MK) to beyond 20 MK. In particular, the capability of observing low-temperature (below 2 MK) plasmas that were not accessible with the Yohkoh Soft X-ray Telescope (SXT), coupled with an order of magnitude higher cadence than SXT, has enabled XRT to make various discoveries on coronal activities. Furthermore, XRT has the unique strength of observing high-temperature plasmas in the corona that are not necessarily well observed with other coronal imagers. The scientific considerations made while designing the XRT and the key points of the instrumental features are reviewed, followed by some highlights of the scientific results obtained with XRT.

The X-Ray Telescope (XRT) on board the Swift satellite is a sensitive imaging spectrometer utilizing a MAT-22 CCD at the Focal plane. The system was designed to operate the CCD at -100 °C +/- 1 °C for the duration of the mission. Due to a failure of the temperature control sub-system, the CCD operates under variable thermal conditions dictated by the view factor of the radiator- heatpipe sub-system to the Earth and sun. A temperature variation of up to 5° C is seen during a single orbit due to the satellite transition from sun light into eclipse and the full operational regime of the instrument ranges from temperatures of -75°C to -45°C due to the persistent heating/cooling effects of satellite orientation to the sun and earth. To maintain the highest quality data products possible from the XRT data stream, a recalibration of the XRT is required to account for this variable thermal environment. We present the methodology for and results from a temperature dependent analysis of on-orbit XRT data, collected during the Swift commissioning phase, used to produce gain, bias and warm pixel calibration products. We also discuss the quality of XRT science products capable with these temperature dependent calibration files and future plans for updates to these calibration products.

The NASA/ASI Imaging X-ray Polarimetry Explorer, which will be launched in\n2021, will be the first instrument to perform spatially resolved X-ray\npolarimetry on several astronomical sources in the 2-8 keV energy band. These\nmeasurements are made possible owing to the use of a gas pixel detector (GPD)\nat the focus of three X-ray telescopes. The GPD allows simultaneous\nmeasurements of the interaction point, energy, arrival time, and polarization\nangle of detected X-ray photons. The increase in sensitivity, achieved 40 years\nago, for imaging and spectroscopy with the Einstein satellite will thus be\nextended to X-ray polarimetry for the first time. The characteristics of gas\nmultiplication detectors are subject to changes over time. Because the GPD is a\nnovel instrument, it is particularly important to verify its performance and\nstability during its mission lifetime. For this purpose, the spacecraft hosts a\nfilter and calibration set (FCS), which includes both polarized and unpolarized\ncalibration sources for performing in-flight calibration of the instruments. In\nthis study, we present the design of the flight models of the FCS and the first\nmeasurements obtained using silicon drift detectors and CCD cameras, as well as\nthose obtained in thermal vacuum with the flight units of the GPD. We show that\nthe calibration sources successfully assess and verify the functionality of the\nGPD and validate its scientific results in orbit; this improves our knowledge\nof the behavior of these detectors in X-ray polarimetry.\n

The Salton Sea Scientific g Project (SSSDP) completed the first major well in the United States Continental Scientific Drilling Program. The well (State 2-14) was drilled to 10,W ft (3,220 m) in the Salton Sea Geothermal Field in California's Imperial Valley, to permit scientific study of a deep, high-temperature portion of an active geothermal system. The program was designed to investigate, through drilling and testing, the subsurface thermal, chemical, and mineralogical environments of this geothermal area. Extensive samples and data, including cores, cuttings, geothermal fluids and gases, and geophysical logs, were collected for future scientific analysis, interpretation, and publication. Short duration flow tests were conducted on reservoirs at a depth of approximately 6,120 ft (1,865 m) and at 10,136 ft (3,089 m). This report summarizes all major activities of the SSSDP, from project inception in the fall of 1984 through brine-pond cleanup and site restoration, ending in February 1989. This report presents a balanced summary of drilling, coring, logging, and flow-test operations, and a brief summary of technical and scientific results. Frequent reference is made to original records, data, and publication of results. The report also reviews the proposed versus the final well design, and operational summaries, such as the bit record, the casing and cementing program, and the coring program. Summaries are and the results of three flow tests. Several teamed during the project.

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will make the first sensitive images of the sky in the high energy X-ray band (6 - 80 keV). The NuSTAR observatory consists of two co-aligned grazing incidence hard X-ray telescopes with a ~10 meter focal length, achieved by the on-orbit extension of a deployable mast. A principal science objective of the mission is to locate previously unknown high-energy X-ray sources to an accuracy of 10 arcseconds (3-sigma), sufficient to uniquely identify counterparts at other wavelengths. In order to achieve this, a star tracker and laser metrology system are an integral part of the instrument; in conjunction, they will determine the orientation of the optics bench in celestial coordinates and also measure the flexures in the deployable mast as it responds to the varying on-orbit thermal environment, as well as aerodynamic and control torques. The architecture of the NuSTAR system for solving the attitude and aspect problems differs from that of previous X-ray telescopes, which did not require ex post facto reconstruction of the instantaneous observatory alignment on-orbit. In this paper we describe the NuSTAR instrument metrology system architecture and implementation, focusing on the systems engineering challenges associated with validating the instantaneous transformations between focal plane and celestial coordinates to within the required accuracy. We present a mathematical solution to photon source reconstruction, along with a detailed error budget that relates component errors to science performance. We also describe the architecture of the instrument simulation software being used to validate the end-to-end performance model.

Hitomi is the 6th Japanese X-ray astronomy satellite launched on 2016 Feb 17. Although it was unfortunately lost about 1 month from the launch, Hitomi produced many new scientific results, owing to extremely high spectral resolution of the non-dispersive SXS detector (X-ray micro-calorimeter). From the observations of the Perseus cluster, a stringent upper limit of the turbulent pressure, only <7% of that of the thermal pressure, is obtained, and the metal abundance in ICM is found consistent to that of the solar vicinity. Power of the high resolution spectroscopy even with small photon counts is demonstrated in N132D and IGR J16318-4848. Emission/absorption line search was performed in Crab and G21.5-0.9. A result is obtained to support that the Crab nebula was born from an electron-capture supernova. New absorption line structures are detected from G21.5-0.9, although they need further confirmation because of low statistical significance of 3-4 sigma. To fulfill the calorimeter science, the XRISM project has been on-going. Following XRISM, we have started preparing the next generation hard X-ray mission FORCE that is a successor of the hard X-ray imager onboard Hitomi, but with much better spatial resolution of 15 arcsec in HPD. They are planned to be launched by the end of March 2022 and late 2020's, respectively.

The First Spacelab mission, launched on Space ShuttleFlight STS-9 in November 1983 carried a multidisciplinary payload which was intended to demonstrate that valuable scientific results can be achieved from such short duration missions. The payload complement included a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment were the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 up to 30 keV. The instrument based on the gas scintillation proportional counter had an effective area of some 180 cm2 with an energy resolution of ∼9% at 7 keV.

The X-ray spectrometer experiment on the first spacelab flight

Scientific ballooning in India

Adjustable X-ray optics is the technology under study by SAO and PSU for the realization of the proposed X-ray telescope Lynx. The technology is based on thin films of lead-zirconate-titanate (PZT) deposited on the back of thermally formed thin substrates, and represents a potential solution to the challenging trade-off between high-surface quality and low mass, that limits the performance of current generation of X-ray telescopes. The technology enables the correction of mirror fabrication figure, mounting induced distortions, and on-orbit correction for variations in the mirror thermal environment. We describe the current state of development, presenting updated test data, anticipation of performances and expectations.

The first true space observatories incorporating imaging telescopes and providing access to the soft X-ray band, but providing some overlapping response into the EUV were flown in the late 1970s and early 1980s. With the Einstein and European X-ray Astronomy Satellite (EXOSAT) satellites, launched in 1978 and 1983 respectively, long exposure times coupled with high point source sensitivity became available to high-energy astronomers for the first time. This progress depended mainly on developments in optics and detector technology but also coincided with a more sophisticated understanding of the physical processes involved in soft X-ray and EUV emission and a better appreciation of the potential significance of observations in these wavebands. This chapter describes the Einstein and EXOSAT missions detailing both the telescope and detector technology. Developments in the understanding of the physical emission processes are outlined to set the context for discussion of the most significant results from these observatories, relevant to the broad field of EUV astronomy.

More than two hundred solar flares, including several GOES X-class events, were successfully observed with the Hard X-ray Telescope (HXT) on board Yohkoh during the initial six months of observations since 1991 October. Hard X-ray images taken simultaneously in four X-ray energy bands (14–23–33–53–93 keV), with angular and temporal resolutions of ~ 5″ and 0.5 s, respectively, have been revealing how and where hard X-rays are emitted in flaring magnetic loops, and further how and where electrons are accelerated and confined. These HXT observations are briefly reviewed from the viewpoint of the instrument capability and performance, with some new scientific results.

The super-massive black-holes in the centers of Active Galactic Nuclei (AGNs) are surrounded by obscuring matter that can block the nuclear radiation. Depending on the amount of blocked radiation, the flux from the AGN can be too faint to be detected by currently flying hard X-ray (above 15 keV) missions. At these energies only ~1% of the intensity of the Cosmic X-ray Background (CXB) can be resolved into point-like sources that are AGNs. In this work we address the question of the undetected sources contributing to the CXB with a very sensitive and new hard X-ray survey: the SIX survey that is obtained with the new approach of combining the Swift/BAT and INTEGRAL/IBIS X-ray observations. We merge the observations of both missions. This enhances the exposure time and reduces systematic uncertainties. As a result we obtain a new survey over a wide sky area of 6200 deg^2 that is more sensitive than the surveys of Swift/BAT or INTEGRAL/IBIS alone. Our sample comprises 113 sources: 86 AGNs (Seyfert-like and blazars), 5 galaxies, 2 clusters of galaxies, 3 Galactic sources, 3 previously detected unidentified X-ray sources, and 14 unidentified sources. The scientific outcome from the study of the sample has been properly addressed to study the evolution of AGNs at redshift below 0.4. We do not find any evolution using the 1/V_max method. Our sample of faint sources are suitable targets for the new generation hard X-ray telescopes with focusing techniques.

We review the history of astronomical X-ray polarimetry based on the author’s perspective, beginning with early sounding-rocket experiments by Robert Novick at Columbia University and his team, of which the author was a member. After describing various early techniques for measuring X-ray polarization, we discuss the polarimeter aboard the Orbiting Solar Observatory 8 (OSO-8) and its scientific results. Next, we describe the X-ray polarimeter to have flown aboard the ill-fated original Spectrum-X mission, which provided important lessons on polarimeter design, systematic effects, and the programmatics of a shared focal plane. We conclude with a description of the Imaging X-ray Polarimetry Explorer (IXPE) and its prospective scientific return. IXPE, a partnership between NASA and ASI, has been selected as a NASA Astrophysics Small Explorers Mission and is currently scheduled to launch in April of 2021.

The thin film technology called "depth-graded multi-layer" is used to manufacture reflector foils, which are inserted in a hard X-ray telescope. When the temperature of the foil changes from the temperature at which the foil was produced; thermal deformation is induced due to difference of linear coefficient of expansion of its constituents. The deformation causes performance of X-ray image formation to deteriorate. Therefore, it is absolutely imperative to estimate the amount of deformation quantitatively and to establish a method of temperature control for the foil under the thermal environment on orbit. We used the hard X-ray telescope, which is part of the currently-projected the ASTRO-H X-ray satellite, as an example for investigation. The effective method of the HXT thermal control was examined with the thermal analytical software, "Thermal Desktop". The deformation of the foil when the temperature was changed by 1 degree C was predicted by a finite element analysis (FEA). The thermal desktop analysis shows that the overall foil temperature in orbit can be close to the temperature at which the foils were produced (&#126;22degree C) by the newly developed thermal control method. The FEM analysis shows that the prediction of the foil deformation due to a temperature change of 1 degree C is about 8 &mu;m.