[vsnet-grb-info 17388] Trigger 668879: Swift detection of V 404 Cyg again

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18778
SUBJECT: Trigger 668879: Swift detection of V 404 Cyg again
DATE:    15/12/30 23:22:00 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

S. D. Barthelmy (GSFC), V. D'Elia (ASDC), L. Izzo (URoma/ICRA),
A. Y. Lien (GSFC/UMBC) and T. Sakamoto (AGU) report on behalf of the
Swift Team:

At 22:44:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located V 404 Cyg (trigger=668879).  Swift was already observing this source. 
The BAT on-board calculated location is 
RA, Dec 306.016, +33.850, which is 
   RA(J2000)  =  20h 24m 04s
   Dec(J2000) = +33d 51' 00"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows activity at ~T-50 sec
and at T_zero, but there is gap in the data from T_zero to T+100 sec. 

The XRT began observing the field at 22:48:41.67 UT, 230.1 seconds after
the BAT trigger. No source was detected in 175 s of promptly
downlinked data. We are waiting for the full dataset to detect and
localise the XRT counterpart. 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
230 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. Results from the 2.7'x2.7' sub-image are
not available at this time. The overlap of the 8'x8' region for the list of
sources generated on-board and the XRT error circle is uncertain. No correction
has been made for extinction. 

This is the second trigger from this source (GCN 18777).  It triggered
while Swift was observing as a result of the first trigger.  As such
XRT and UVOT have data before and during T_zero for this second trigger.