GCN Circular 13203

V. D'Elia (ASDC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
S. Campana (INAF-OAB), M. M. Chester (PSU), J. A. Kennea (PSU),
C. B. Markwardt (NASA/GSFC), A. Maselli (INAF-IASFPA),
A. Melandri (INAF-OAB), P. T. O'Brien (U Leicester),
T. Sakamoto (NASA/UMBC), C. J. Saxton (UCL-MSSL),
B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), G. Stratta (ASDC),
C. A. Swenson (PSU), T. N. Ukwatta (MSU) and B.-B. Zhang (PSU) report
on behalf of the Swift Team:

At 20:33:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120403B (trigger=519256).  Because of an observing constraint,
the slew to the burst was delayed by 12.9 minutes. 
The BAT on-board calculated location is 
RA, Dec 54.809, -89.037, which is 
   RA(J2000)  =  03h 39m 14s
   Dec(J2000) = -89d 02' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several spikes
with a total duration of about 10 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 20:49:04.0 UT, 907.5 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 55.33838, -89.00933 which is equivalent
to:
   RA(J2000)  = 03h 41m 21.21s
   Dec(J2000) = -89d 00' 33.6"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 104 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 9.52
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 910 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 100% of
the XRT 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
XRT 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
0.13. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)