TITLE:   GCN CIRCULAR
NUMBER:  27297
SUBJECT: GRB 200303A: Swift detection of a burst
DATE:    20/03/03 02:49:25 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

S. B. Cenko (GSFC), S. D. Barthelmy (GSFC), C. Gronwall (PSU),
J.D. Gropp (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), M. J. Moss (GWU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 02:34:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200303A (trigger=959431).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 212.698, +51.360, which is 
   RA(J2000)  =  14h 10m 47s
   Dec(J2000) = +51d 21' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multi-peak
structure with a duration of about 60 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 02:36:25.1 UT, 87.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 212.7173, 51.3583 which is equivalent to:
   RA(J2000)  = 14h 10m 52.15s
   Dec(J2000) = +51d 21' 29.9"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 43 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 8.77e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 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
0.02. 

This source lies within the current (Sector 22) field-of-view of TESS camera 3. 

Burst Advocate for this burst is S. B. Cenko (brad.cenko 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/)