[vsnet-j 2202] V4641 Sgr extremely short and violent flares!

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

V4641 Sgr extremely short and violent flares!

Dear Colleagues,

    We have finished analyzing July 7 data by Tanabe-san (Okayama U. Sci.,
5s exposure).  [We are also analyzing the data from Torii-san, RIKEN, but
the analysis is slightly delayed].

    The data are truly amazing!  There is an unmistakable 1 mag short
flare.  The flare rise and fade was recorded in detail on sequential
images.  The 1 mag rise took only 30s!  The actual maximum may have been
even brighter (could have been a brightness spike) as inferred from the
light curve.  There were also multiple smaller flares (0.3 mag) with
typical durations less than 1 min.

    As can be easily guessed from this light curve, such short flares
musy have been effectively smoothed out on long exposure images.
Please use integeration times of ~5s (or even less with a large telescope)!

    More detailed analysis is in progress.

Regards,
Taichi Kato
VSNET Collaboration team

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