Surveys of X-Ray Sources
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My assignment this afternoon is to review briefly the status of the observational work that has been accomplished since the last IAU discussion of X-ray astronomy which took place at the Liège Symposium 3 years ago. Essentially, the methods of observation have not changed in any significant way. All of the information has come from small rockets, on the order of the Aerobee and the Skylark in size, and from packages carried on balloons. The quality of the surveys varies according to the objectives of each experiment. For example, my colleagues and I, at the Naval Research Laboratory, have attempted to perform broad-sky surveys to fill the picture of the general distribution of sources in space and, as a result, have had to sacrifice precision in position and high resolution. At the other extreme, Dr. Giacconi and his colleagues, at American Science and Engineering, Inc. and the Massachusetts Institute of Technology, have concentrated the available flight time on individual sources and have achieved remarkably high positional accuracy for some of the stronger sources — sufficient to associate them with optical objects. Dr. Fisher and his colleagues at Lockheed have taken an intermediate approach and used fan beam scans of limited regions of the sky, which give more precise position and better resolution in one dimension than the broad NRL surveys.
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