TITLE:   GCN CIRCULAR
NUMBER:  14411
SUBJECT: GRB 130420B: Swift detection of a burst
DATE:    13/04/20 13:14:19 GMT
FROM:    David Burrows at PSU/Swift  <burrows@astro.psu.edu>

S. R. Oates (UCL-MSSL), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
V. D'Elia (ASDC), N. Gehrels (NASA/GSFC), S. T. Holland (STScI),
N. P. M. Kuin (UCL-MSSL), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), M. H. Siegel (PSU) and
E. Sonbas (NASA/GSFC/Adiyaman Univ.) report on behalf of the Swift
Team:

At 12:56:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130420B (trigger=553996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 183.120, +54.386 which is 
   RA(J2000) = 12h 12m 29s
   Dec(J2000) = +54d 23' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 12:57:25.6 UT, 54.5 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. About 8 seconds of data were obtained in WT mode before Swift 
slewed away from the field, indicating a bright X-ray source in the field, 
but no position is available from the WT data. No XRT position will be 
available until data from the second orbit are processed. 

UVOT took a finding chart exposure of	8 seconds with the White filter
starting 57 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. 
Results from the list of sources generated on-board are not available at this
time. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is S. R. Oates (samantha.oates AT ucl.ac.uk). 
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.)