[vsnet-grb-info 18252] Swift Trigger 704327: a possible GRB

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19700
SUBJECT: Swift Trigger 704327: a possible GRB
DATE:    16/07/14 05:43:20 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

B. Sbarufatti (INAF-OAB/PSU), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 05:21:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible GRB (trigger=704327).  Swift slewed immediately 
to the location.  The BAT on-board calculated location is 
RA, Dec 272.613, +72.056 which is 
   RA(J2000) = 18h 10m 27s
   Dec(J2000) = +72d 03' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a weak peak
structure with a duration of about 10 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 05:22:55.3 UT, 109.0 seconds after
the BAT trigger. No source was detected in 396 s of promptly downlinked
data, which covered 91% of the BAT error circle. We are waiting for the
full dataset to detect and localise the XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 113 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.04. 

Given the weak peak in the rate data, the marginal significance
of the image detection (6.75 sigma initially, dropping to 5.9 sigma
after ground processing) and the lack of detection by the initial
XRT data, we cannot confirm that this is a true astrophysical
event. 

A final determination of the nature of this trigger will require
the full downlinked dataset. 

Burst Advocate for this burst is B. Sbarufatti (boris.sbarufatti AT brera.inaf.it). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)