Abstract
THE Copernicus orbiting observatory contains two astronomical experiments, the Princeton ultraviolet spectrometer and the MSSL X-ray package. They are coaligned, and during ultraviolet observations the 3–8 keV collimated proportional counter routinely collects background data1. When the observatory was pointed at the ultraviolet target γ Cas on December 21, 1975 and again on January 20, 1976, a clear excess of counts was seen in the 3–8 keV channel compared to preceding and following targets. This count rate corresponds to a flux at the Earth of ∼ 1.2×10−10 erg cm−2S−1, and lies 5σ above the mean background level determined from several weeks of observations (Table 1).
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MASON, K., WHITE, N. & SANFORD, P. X-ray emission from γ Cas. Nature 260, 690–691 (1976). https://doi.org/10.1038/260690a0
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DOI: https://doi.org/10.1038/260690a0
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