Abstract
As part of regular monitoring of variable X-ray sources with the University College London–Mullard Space Science Laboratory X-ray instrumentation on the Copernicus satellite, we have observed Cyg X-1 continuously for 12 d between 22 October and 3 November, 1975. The X-ray flux was noted to be more variable than it had been during previous monitoring runs, when the source had been in its low state1, and, in particular, a marked increase in flux occurred 8 d into the observing run (∼ October 29.5 UT, 1975). After this date, the mean 3–8-keV flux increased steadily, and by 3 November had risen by 30% compared with its level during the first part of the observation. The X-ray flux data, integrated in time blocks of 30 min, are shown in Fig. 1b. In Fig. 1a we show the spectral hardness ratio (defined as the 5.5–8.0-keV flux divided by the 3.0–5.5-keV flux) integrated over intervals of 0.5 d. This quantity decreased progressively after 30 October, until by 3 November it was down by an amount equivalent to a drop of 0.1 in the power law spectral index of the source.
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References
Sanford, P. W., Ives, J. C., Bell-Burnell, S. J., Mason, K. O., and Murdin, P., Nature, 256, 109 (1975).
Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., IAU Circ., No. 2863 (1975).
Grindlay, J., Schreier, E., den Boggende, A., and Brinkmann, A., IAU Circ., No. 2863 (1975).
Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., IAU Circ., No. 2879 (1975).
Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., Nature, 261, 213 (1976).
Walker, E. N., Mon. Not. R. astr. Soc., 160, 9P (1972).
Walker, E. N., and Rolland, Q. A., Mon. Not. R. astr. Soc., 169, 247 (1974).
Walker, E. N., Rolland, Q. A., and Buck, C. S., Mon. Not. R. astr. Soc. (in the press).
Hutchings, J. B., Astrophys. J., 188, 341 (1974).
Avni, Y., and Bahcall, J. N., Astrophys. J., 197, 657 (1975).
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WALKER, E., BROWNLIE, G., MASON, K. et al. Optical behaviour of HDE226868 during a Cyg X-1 X-ray transition. Nature 263, 393–395 (1976). https://doi.org/10.1038/263393a0
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DOI: https://doi.org/10.1038/263393a0
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