Variability of Cyg X-1 (V1357 Cyg) in 1995-1996 during the Hard and Soft X-ray Spectral States

Details Variability of Cyg X-1 (V1357 Cyg) in 1995-1996 during the Hard and Soft X-ray Spectral States Variability of Cyg X-1 (V1357 Cyg) in 1995-1996 during the Hard and Soft X-ray Spectral States

Jan 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000astl...26...22k&link_type=abstract

Astronomy Letters, vol. 26, p. 22-33 (2000)

Astronomy and Astrophysics

Astronomy

3

Scientific paper

We report photoelectric UBVR observations of Cyg X-1 with the 1-m Tien-Shan and 48-cm Mount Maidanak reflectors from October 1995 through November 1996. The orbital light curve is represented by the model of a tidally deformed star. Various types of flare and fading are observed. The optical and X-ray (ASM/RXTE 2-10 keV) variabilities are compared. A 90-day soft X-ray outburst occurred in the summer of 1996, but no similar event was detected at optical wavelengths. Nevertheless, an interrelation was found between the variabilities in these bands, suggesting that they are affected by the same processes. A correlation between changes in the mean X-ray and optical fluxes was found after the 90-day X-ray outburst and the mean optical orbital light curve were subtracted. A Fourier analysis reveals common features in Fourier spectra of the X-ray and optical data. An orbital X-ray variability with a 5.6-percent amplitude is confirmed. Optical flares with a 0.04-mag amplitude and a duration of several days, which coincided with local X-ray minima, were detected. The optical brightness of Cyg X-1 declined by 0.04-mag in about a week early in November 1996. A possible physical interpretation of the flares and the orbital X-ray variability in terms of accretion instability is offered. The characteristic time it takes for matter to pass through the accretion structure is estimated directly from observations; it was approximately a week in 1996.

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