TITLE:   GCN CIRCULAR
NUMBER:  13049
SUBJECT: GRB 120312A: Swift detection of a burst
DATE:    12/03/12 16:33:53 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

M. Stamatikos (OSU/NASA/GSFC), S. Campana (INAF-OAB),
M. M. Chester (PSU), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
S. T. Holland (STScI), J. A. Kennea (PSU), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA),
A. Melandri (INAF-OAB), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), M. C. Stroh (PSU), C. A. Swenson (PSU),
G. Tagliaferri (INAF-OAB) and B.-B. Zhang (PSU) report on behalf of
the Swift Team:

At 16:06:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120312A (trigger=517566).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 251.764, +23.857 which is 
   RA(J2000) = 16h 47m 03s
   Dec(J2000) = +23d 51' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked FRED
structure with a duration of 12 about sec.  The peak count rate
was ~1300 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Using promptly downlinked data we find an uncatalogued X-ray source
with an enhanced position: RA, Dec 251.7885, 23.8586 which is
equivalent to:
   RA(J2000)  = 16h 47m 09.23s
   Dec(J2000) = +23d 51' 30.8"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). 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 in excess of the Galactic value (4.08 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 1.7
(+1.51/-1.34) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 112 s 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
0.07. 

Burst Advocate for this burst is M. Stamatikos (Michael.Stamatikos-1 AT nasa.gov). 
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.)