Abstract
Sampling observations of a complete 35d cycle of Her X-1 during 1 March to 5 April 1984 with the low and medium energy X-ray detectors of EXOSAT are presented. The intensities measured in the Argon detectors are compared with the UHURU 35d light curve to obtain the turn-on times of two consecutive cycles as JD 2445753.0 ± 1.0, and JD 2445788.0 ± 0.5. The low energy data is used to determine the rotation period and its derivative as: 1.23779200 s ± 50 ns, and (-2 ± 1) × 10-13 respectively, at the epoch JD 2445778.56. Analysis of the pulse arrival phases indicate that during mid-on phase of the 35d cycle there is shift of about 180°. Evidence for the long term correlated changes of P35 and P1.24s is presented, confirming the low quality of the 35d clock and suggesting that the basic clock mechanism must lie in the disk structure itself.
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Ögelman, H., Kahabka, P., Pietsch, W. et al. 35 Day cycle and the rotation period of Her X-1. Space Sci Rev 40, 347–353 (1985). https://doi.org/10.1007/BF00212907
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DOI: https://doi.org/10.1007/BF00212907