GCN Circular 27326

J.D. Gropp (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
J. A. Kennea (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), B. Sbarufatti (PSU), M. H. Siegel (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 22:50:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200306C (trigger=960102).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 198.582, +11.255 which is 
   RA(J2000) = 13h 14m 20s
   Dec(J2000) = +11d 15' 18"
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 50 sec.  The peak count rate
was ~1800 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 22:52:35.9 UT, 116.9 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 198.55562, 11.26981 which
is equivalent to:
   RA(J2000)  = 13h 14m 13.35s
   Dec(J2000) = +11d 16' 11.3"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 107 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
https://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 (1.91 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.8
(+2.73/-2.37) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
117 seconds after the BAT trigger. There is a candidate afterglow in the list
of sources generated on-board at
  RA(J2000)  =	13:14:13.44 = 198.55602
  DEC(J2000) = +11:16:11.5  =  11.26985
with a 90%-confidence error radius of about 1.10 arc sec. This position is 1.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.47. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is J.D. Gropp (jdg44 AT psu.edu). 
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/)