[vsnet-alert 8464] Re: V4641 Sgr active !!

[Makoto Uemura]

Re: V4641 Sgr active !!

    According to the ASAS3 system, no sign of the outburst can be 
seen before 23.21 June.  Recent observations posted to VSNET are:

SGRV4641        050502.805     148C  Myy
SGRV4641        050504.762     142C  Myy
SGRV4641        050507.73442 13.78V  Mhh
SGRV4641        050512.653     142C  Myy
SGRV4641        050531.71027 13.84V  Mhh
SGRV4641        050604.702     <138  Mdy
SGRV4641        050605.710     <138  Mdy
SGRV4641        050609.587     144C  Myy

    The object showed a very bright (8.9mag) outburst which lasted 
only for one day in September 1999.  Relativistic jets were associated 
with this outburst.  
    After 1999, optical outbursts were recorded in May 2002, August 2003, 
and July 2004.  All of them showed similar characteristics, and 
different from that observed in 1999.  X-ray luminosities during these 
three outbursts are much smaller than that in 1999.  So, these outbursts 
are rather lower energetic events.  Interestingly, the object frequently 
showed rapid variations during the outbursts in 2002--2004.  
Such optical rapid variations imply that the optical emission originated 
from a vicinity of a black hole or jets.  Now, you may be able to see 
a black hole with your eyes.

    Studies of V4641 Sgr have been very difficult because the object 
changed their states very rapidly; outbursts lasted only for one week, 
and even during outbursts, characteristics of variations dramatically 
changed day by day.  So, dense time-series observations with short 
exposure times are needed.

Regards,
Makoto Uemura
Hiroshima University