Optical behaviour of HDE226868 during a Cyg X-1 X-ray transition

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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

  1. 1

    Sanford, P. W., Ives, J. C., Bell-Burnell, S. J., Mason, K. O., and Murdin, P., Nature, 256, 109 (1975).

  2. 2

    Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., IAU Circ., No. 2863 (1975).

  3. 3

    Grindlay, J., Schreier, E., den Boggende, A., and Brinkmann, A., IAU Circ., No. 2863 (1975).

  4. 4

    Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., IAU Circ., No. 2879 (1975).

  5. 5

    Holt, S. S., Kaluzienski, L. J., Boldt, E. A., and Serlemitsos, P. J., Nature, 261, 213 (1976).

  6. 6

    Walker, E. N., Mon. Not. R. astr. Soc., 160, 9P (1972).

  7. 7

    Walker, E. N., and Rolland, Q. A., Mon. Not. R. astr. Soc., 169, 247 (1974).

  8. 8

    Walker, E. N., Rolland, Q. A., and Buck, C. S., Mon. Not. R. astr. Soc. (in the press).

  9. 9

    Hutchings, J. B., Astrophys. J., 188, 341 (1974).

  10. 10

    Avni, Y., and Bahcall, J. N., Astrophys. J., 197, 657 (1975).

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