[vsnet-chat 145] Re: on optical behavior of Cyg X-1 = V1347 Cyg

[Erik Kuulkers <e.kuulkers1@physics.oxford.ac.uk>]

On Thu, 27 Feb 1997, Taichi Kato wrote:
> Subject: [vsnet-chat 140] on optical behavior of Cyg X-1 = V1347 Cyg
> 
>    In IBVS 4404, E. A. Karitskaya and V. P. Goranskij report an unusual
> fading of V1357 Cyg (Cyg X-1) in early November, 1996.  They report a
> transient ~0.04 mag fading in V.  I wonder whether this optical fading
> is somehow related to the recent soft-hard transition in August, 1996
> (S. N. Zhang et al. IAUC 6447).

The so-called "soft state" of Cyg X-1 lasted from mid may to mid august.
Judged from the X-ray light curves, the transition back to the so-called 
"hard state" was definately over by the time of the observations of
Karitskaya & Goranskij in early November, 1996.

>    Wouldn't it be a nice target for CCD photometrists for future X-ray-to-
> optical correlation study?

It would be therefore good to monitor such optically bright X-ray 
binaries, in order to look for such optical transitions, and to correlate 
it with the X-ray behaviour.

Erik Kuulkers

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