GCN Circular 15915

P. A. Evans (U Leicester), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), S. T. Holland (STScI),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Maselli (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. H. Siegel (PSU) and
T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 13:22:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140304A (trigger=590206).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 30.668, +33.485 which is 
   RA(J2000) = 02h 02m 40s
   Dec(J2000) = +33d 29' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a total duration of about 20 sec.  The peak count rate
was ~3600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 13:23:46.2 UT, 75.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 30.6412,
33.4744 which is equivalent to:
   RA(J2000)  = 02h 02m 33.90s
   Dec(J2000) = +33d 28' 27.9"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 89 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 5.98
x 10^20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 6.28e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
137 seconds after the BAT trigger. No credible afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image processing FAILED
because of no aspect solution. 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 0.08. 

This GRB will enter a Moon observing constraint around 20:00 UT and
will not be observable again by Swift until March 6 (Thursday) around
05:30 UT. 

Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.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.)