[vsnet-alert 3980] RXJ0640-24 outburst update

[Taichi Kato <tkato>]

RXJ0640-24 outburst update

Dear Colleagues,

    As notified by Uemura-san, RX J0640-24 is apparently quickly fading
from outburst.  The possible superhump-like feature observed in the Jan. 7
data seems to have decayed on Jan. 8 data.  However, there looks like
some evidence of modulations with a likely period less than an hour.
During the 3.4-hour run, the object showed little trend of the continuing
rapid fading.  This precludes the possible explanation of the Jan. 7
variation as the effect of extinction.  The rapid rate of decline (~1 mag/day
between Jan. 6 and 8) suggests that the object can be a short-period system
(e.g. SU UMa stars).  It is not surprizing such a system may show transient
superhump activities during a short outburst, or a precursor to a
superoutburst (the good example is the superoutburst of SU UMa in 1998
December).  Observers are strongly requested to continue monitoring the
activity of the object for short-term variations on coming nights, and
to look for a possible (immediate or future) superoutburst.  The campaign
is still ongoing, and please keep us in touch.

Regards,
Taichi Kato and Makoto Uemura

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