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Abstract
The primary mission of the A-1 instrument aboard the first N. A. S. A. High Energy Astronomical Observatory (HEAO) is to enlarge the catalogue of X-ray sources to about 1000. Seven modules of X-ray proportional counters, having an average effective aperture of about 1700 cm 2 apiece, cover an energy range from 0.25 keV to about 25 keV. Full sky coverage is obtained by spinning the spacecraft at 2 rev. h -1 about the direction to the Sun. The detectors view the sky at right angles to the spin axis, so that 48 great circle sweeps normal to the ecliptic plane are completed each day. As the Earth carries the spacecraft around the Sun, the scan plane rotates 1° in ecliptic latitude each day. The basic scan is obtained with four modules having 1° x 4° collimation, giving 10000 resolution elements on the full sky. Assuming one source detection for every ten resolution elements, the survey should detect about 1000 sources.
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Schedule a callMore From: Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences
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