TITLE:   GCN CIRCULAR
NUMBER:  27102
SUBJECT: GRB 200216B: Swift detection of a burst
DATE:    20/02/16 13:57:44 GMT
FROM:    Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>

P. D'Avanzo (INAF-OAB), M. G. Bernardini (INAF-OAB), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. J. Klingler (PSU), A. Y. Lien (GSFC/UMBC),
T. Sbarrato (INAF-OAB) and A. Tohuvavohu (U Toronto) report on behalf
of the Neil Gehrels Swift Observatory Team:

At 13:32:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200216B (trigger=956824).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 160.461, +19.454 which is 
   RA(J2000) = 10h 41m 51s
   Dec(J2000) = +19d 27' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed one long peak
with a duration of about 30 sec, there is possible evidence for weaker 
emission out to T0+60 seconds. The peak count rate was ~2000 counts/sec 
(15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 13:34:29.0 UT, 115.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
160.4343, 19.4757 which is equivalent to:
   RA(J2000)  = 10h 41m 44.23s
   Dec(J2000) = +19d 28' 32.4"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 119 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 (2.03 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 9.9
(+3.22/-2.80) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.33e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 124 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. 

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