Abstract
We have used the twin 11-m diameter mirrors of the NASA Jet Propulsion Laboratory's solar energy facility to observe high-energy γ rays from Cyg X-3 using the atmospheric Cerenkov technique. Observations of photons with energies above 1012 eV modulated with the 4.8 h period of the X-ray source have been reported previously by the Crimean Astrophysical Observatory1–6 and the Fred Whipple Observatory7,8. We report here data from ∼105 air shower events obtained 29 August–6 September 1981 with an approximate threshold energy of 500 GeV. A positive signal with an amplitude of 10.9±2.5% of the background cosmic ray rate appears near phase 0.6 of the 4.8-h cycle, in which phase 0.0 corresponds to minimum X-ray emission. This observation, together with previous Cerenkov detections, indicates that the high energy emission from Cyg X-3 is evolving on a time scale of a few years which suggests a recent origin for the system in its present form.
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Lamb, R., Godfrey, C., Wheaton, W. et al. Cygnus X-3 observed at photon energies above 500 GeV. Nature 296, 543–544 (1982). https://doi.org/10.1038/296543a0
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DOI: https://doi.org/10.1038/296543a0
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