Physics – Optics
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000abaob..75..241k&link_type=abstract
Bulletin of the Abastumani Astrophysical Observatory, Vol. 75, p. 241-268
Physics
Optics
Scientific paper
Broad-band photometric observations of the black hole candidate Cyg X-1 were carried out in 1975-1998 at the Abastumani Astrophysical Observatory in the framework of coordinated observations, at the varies observatories of the former Soviet Union. All data have been reduced to a homogeneous set.Comparison of the optical and X-ray data clearly shows the existence of several kinds of variability.
Analysis of the prolonged photoelectric observations of V 1357 Cyg=Cyg X-1 confirmed long-period optical variation of this X-ray binary system with the period of 294 d revealed by Kemp et al. This periodicity is most strongly pronounced at the orbital period phase when the optical star is in front of the X-ray source. Variations of the mean level of Cyg X-1 and of the light curve form with the phase of the period 294 d agree well with the model of the precessing accretion disk which radiates in the optical range mainly by scattering and processing of the optical star radiation. The direction of the disc precession coincides with that of the orbital motion and it is hard to understand this fact in the models with the forced precession. The triple system model is less probable.
There are also observations of this objects made in the Abastumani Observatory in 1982-1988 which are represented the Table and light curves. These observations have not discussed by coordinators.
The observations taken in the course of the International campaign "The Optical Monitoring of the Unique Astrophysical Objects" were realized by the observatories located on the territories of Georgia, Russia, Uzbekistan and Ukraine in 1994-1998. They are united in a single set, taking into account the systemic differences between them. Number of usual observations is 2247 in 399 nights in U B V R bands.
The observations were performed simultaneously in X-ray band in the energy range of 2-10 keV (ASM/RXTE), and 20-100 keV (BASTE/CGRO), and also with radio observations at the Mullard radio observatory. Our optical data overlapped well the hard band at JD 2451000-040. Both outbursts did not coincide with any optical brightening or double wave orbital light curve changes. From two independent sets strong optical flare at JD 2450988, being a possible precursor of hard X-ray flare have been detected. Intrinsic variations of the system have the chaotic character with flares and dips in time scale of a day and the amplitude of 0.10 m.
Fourier spectra show predominating secondary period of 147 d at high probability level, being a half of 294 d period found by Priedhorsky et al. in X-rays, and Kemp et al. in optics. We have identified near-by period of 150 d which predominates modern X-ray light curve. The period found in optics is close to the period of 142.7 d in modern Mullard radio data by Brooksopp et al.
The light curve resembles a non-stationary process by the time changes of Fourier spectra. But some spectrum peaks can be stable for several seasons.
The cross-correlation analysis confirms the time delay of the trends of the X-ray light curve relative to the optical one by 11.620 days. The weak relation of the short-time variations of X-ray and optical radiation are also found at high probability level with delay 3 days.
Kochiashvili N. T.
Kumsiashvili M. I.
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