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The meeting of the High Energy Astrophysics Division of the American Astronomical Society, held in Cambridge, Massachusetts on January 28- 30, 1980, marks the coming of age of X-ray astronomy. In the 18 years since the discovery of the first extrasolar X-ray source, Sco X-l, the field has experienced an extremely rapid instrumentation development culminating with the launch on November 13, 1978 of the Einstein Observatory (HEAO-2) which first introduced the use of high resolution imaging telescopes to the study of galactic and extragalactic X-ray sources. The Einstein Observatory instruments can detect sources as faint as 10-7 Sco X-lor about 17 magnitudes fainter. The technological developments in the field have been paralleled by a host of new discoveries: in the early 1960's the detection of 9 "X-ray stars", objects 10 times more luminous in X-rays than the Sun and among the brightest stellar objects at all wavelengths; in the late 1960's and early 1970's the discovery of the nature of such systems which were identified as collapsed stars (neutron stars and black holes) in mass exchange binary systems, and the detection of the first few extragalactic sources.
This book gives an account of the proceedings of the International Astronomical Union Colloquium 115: High Resolution X-Ray Spectroscopy of Cosmic Plasmas. This was the first IAU meeting dedicated to high resolution X-ray spectroscopy of objects outside the solar system. A broad range of objects and astrophysical conditions are discussed. Results from the first generation of satellites with spectroscopic capability, i.e. the Einstein Observatory, EXOSAT, and Tenma, are reviewed from a perspective of a more precise interpretation allowed by improved theoretical models and plasma diagnostics. Laboratory and solar X-ray results that model or are relevant to conditions found in cosmic X-ray sources are also presented. The colloquium presents a forum for discussion of scientific objectives of new international missions in high resolution X-ray spectroscopy.
The idea for this text emerged over several years as the authors participated in research projects related to analysis of data from NASA's RHESSI Small Explorer mission. The data produced over the operational lifetime of this mission inspired many investigations related to a specific science question: the when, where, and how of electron acceleration during solar flares in the stressed magnetic environment of the active Sun. A vital key to unlocking this science problem is the ability to produce high-quality images of hard X-rays produced by bremsstrahlung radiation from electrons accelerated during a solar flare. The only practical way to do this within the technological and budgetary limitations of the RHESSI era was to opt for indirect modalities in which imaging information is encoded as a set of two-dimensional spatial Fourier components. Radio astronomers had employed Fourier imaging for many years. However, differently than for radio astronomy, X-ray images produced by RHESSI had to be constructed from a very limited number of sparsely distributed and very noisy Fourier components. Further, Fourier imaging is hardly intuitive, and extensive validation of the methods was necessary to ensure that they produced images with sufficient accuracy and fidelity for scientific applications. This book summarizes the results of this development of imaging techniques specifically designed for this form of data. It covers a set of published works that span over two decades, during which various imaging methods were introduced, validated, and applied to observations. Also considering that a new Fourier-based telescope, STIX, is now entering its nominal phase on-board the ESA Solar Orbiter, it became more and more apparent to the authors that it would be a good idea to put together a compendium of these imaging methods and their applications. Hence the book you are now reading.
This final report summarizes our past activities and discusses the work performed over the period of 1 April 1990 through 1 April 1991 on x-ray optics, soft x-ray (0.1 - 10 KeV) imaging detectors, and hard x-ray (10 - 300 KeV) imaging detectors. If microchannel plates (MCPs) can be used to focus x-rays with a high efficiency and good angular resolution, they will revolutionize the field of x-ray optics. An x-ray image of a point source through an array of square MCP pores compared favorably with our ray tracing model for the MCP. Initial analysis of this image demonstrates the feasibility of MCPs for soft x-rays. Our work continues with optimizing the performance of our soft x-ray MCP imaging detectors. This work involves readout technology that should provide improved MCP readout devices (thin film crossed grid, curved, and resistive sheets), defect removal in MCPs, and photocathode optimization. In the area of hard x-ray detector development we have developed two different techniques for producing a CsI photocathode thickness of 10 to 100 microns, such that it is thick enough to absorb the high energy x-rays and still allow the photoelectrons to escape to the top MCP of a modified soft x-ray imaging detector. The methods involve vacuum depositing a thick film of CsI on a strong back, and producing a converter device that takes the place of the photocathode. Murray, S. S. and Schwartz, D. A. NASA-CR-193653, NAS 1.26:193653 NAG5-605...
"It may be obvious why visible astronomy utilizes images, but it is illustrative to consider the value of focusing to X-ray astronomy. A list of advantages offered by the best possible two-dimensional angular resolution would include: (i) Resolving sources with small angular separation and distinguishing different regions of the same source. (ii) Using the image morphology to apply intuition in choosing specific models for quantitative fits to the data. (iii) Using as a "collector" to gather photons. This is necessary because X-ray-source fluxes are so low that individual X-ray photons are detected; the weakest sources give less than one photon per day. (iv) Using as a "concentrator," so that the photons from individual sources interact in such a small region of the detector that residual non-X-ray background counts are negligible. (v) Measuring sources of interest and simultaneously determining the contaminating background using other regions of the detector. (vi) Using with dispersive spectrometers such as transmission or reflection gratings to provide high spectral resolution. The Earth's atmosphere completely absorbs cosmic X-rays. Consequently, X-ray observatories must be launched into space; so size, weight, and cost are always important constraints on the design. In practice this leads to a trade-off between the best possible angular resolution and the largest possible collecting area. Realizing an X-ray telescope involves two key issues: reflection of X-rays, and formation of an image"--