[vsnet-campaign-xray 11] (fwd) Renewed activity in V4641 Sgr (XTE J1819-254)

[Taichi Kato <tkato>]

(fwd) Renewed activity in V4641 Sgr (XTE J1819-254)

Date: Mon, 17 Jul 2000 22:19:03 -0600
From: "Robert M. (Bob) Hjellming" <rhjellmi@cv3.cv.nrao.edu>
Subject: Renewed activity in V4641 Sgr (XTE J1819-254) 

>Collegues,

     In looking at the 4th superluminal source (our paper will be published 
in Ap. J. in the
Nov. 10 issue) during our usual monitoring of previous microquasars 
(AH669)  early July 17 UT
we detected V4641 Sgr as a 1.6 mJy source at 8.4 GHZ.  A peek at it 
tonight, a bit less than
24 hours later, confirms the detection and indicates a decay to 1 mJy.

     In sending the usual private advance announcement to many who observe 
this type
of object, I got a response back from an X-ray astronomer that the group at 
Oxford
told him it had resumed optical activity a week ago!   I do not know what 
is really going
on, but the radio re-detection, and decay change in 1 day, is real.  V4641 
Sgr is a source
with recurrent activity.

     In any case, the radio source may have peaked at some high level 
during the last week
and we are seeing the decay, but the indication is a roughly flat spectrum 
between
4.9 and 8.4 GHz earlier tonight.  I have more data at 1.49 and 14.9 GHz, 
but a glitch in real-time FILLM
will delay calibration until I get the data tapes tomorrow.

      I am begging for VLA time tomorrow, and we have slots to look at it 
the following two
days.

      This is to confirm the previous radio report of a weak radio source
at the location of V4641 Sgr.  The VLA is now in its smallest 1 km 
configuration, so
no useful imaging is likely and we see, and probably will only see, an 
unresolved source.

Cheers, Bob

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