TITLE:   GCN CIRCULAR
NUMBER:  22478
SUBJECT: GRB 180314A: Swift detection of a burst with an optical counterpart
DATE:    18/03/14 00:57:37 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

P. D'Avanzo (INAF-OAB), A. Deich (PSU), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), B. Sbarufatti (PSU),
M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 00:43:31 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180314A (trigger=814129).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 99.276, -24.491 which is 
   RA(J2000) = 06h 37m 06s
   Dec(J2000) = -24d 29' 28"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 40 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 00:46:10.6 UT, 159.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 99.26519, -24.49603 which
is equivalent to:
   RA(J2000)  = 06h 37m 03.65s
   Dec(J2000) = -24d 29' 45.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 39 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 1.50
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 1.58e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 166 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	06:37:03.68 =  99.26532
  DEC(J2000) = -24:29:46.0  = -24.49612
with a 90%-confidence error radius of about 0.61 arc sec. This position is 2.8
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.27 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.08. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo 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.)