[vsnet-campaign-news 158] Microquasar V4641 Sgr resumed its activity!

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

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       The Galactic Microquasar V4641 Sgr resumed its activity!
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     This Galactic microquasar (see the most recent AstroAlert issues)
had become rather inactive after reaching its peak around May 24.
However, the object has apparently "turned on" again since June 2.
The report based on June 4 observations (Makoto Uemura, Kyoto University)
follows:

        The light curve on June 4 taken at Ouda shows a large 
    (amplitude=1.2mag) hump and many 0.2mag-small flares.  
    The large hump has a peak at about June 4.65UT and a duration of ~3 hr. 
    The small flares looks have a weak, but characteristic 
    periodicity (50-100s).
    After the object experienced the hump, it returned at quiescent 
    level.  Follow-up observations are encouraged since amplitudes 
    of modulations seem to become larger with time.

     Comparing these data with May 31-June 1 observations reported by
Gianluca Masi and Franco Mallia at Campo Catino Astronomical Observatory,
it has become evident that the source has resumed its activity.  Please keep
in mind that the huge 1999 September event was preceded month-long activity
phase (sometimes looking interrupted by inactive phases).  There may be a
coming major flare-up.  Please continue observing the object as intensively
as you can!

    We have put on the VSNET webpage a new light curve drawn from the June 4
observation.  The amplitude of the variation surpassed that on May 24.
You can see the activity the object showed only half a day ago!

    http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Xray/v4641sgr02.html

Regards,
Taichi Kato
VSNET Collaboration team

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  VSNET (Variable Star Network) is an international variable star observing
network, covering various areas of novae, supernovae, cataclysmic variables
(CVs), X-ray transients, and other classical eruptive, pulsating, and
eclipsing variables.  VSNET is one of invited contributing organizations
to the SkyPub AstroAlert system.

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