An all-sky camera battery for x-ray astronomy

Abstract

The increasing number of interesting variable X-ray sources asks for an instrument for continuously monitoring the brightness of the most important X-ray sources over the whole sky. We describe a system consisting of a set of identical large position-sensitive detectors, mounted on the sides of a polyhedral satellite. Each counter is illuminated through a large diaphragm, with binary shadow characteristics. By holographic methods the X-ray image of the observed part of the sky could be derived from the illumination of each detector by multiplex analysing methods. The satellite should have fairly coarse (half a degree accuracy) three-axial stabilization, and an on-board computersteered data accumulation system.

A relation is derived between the number of transparent holes in the diaphragm, the total count rate, and the flux of the faintest observable source. It appears that for a diaphragm with a few hundred transparent holes (detector geometrical area ≈10³ cm²) an integration time of approximately 6 min is needed in order that sources with a count rate of 0.01 cm⁻² s⁻¹ should still be observable with a confidence limit of 99%.