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GCN Circular 27254

Subject
GRB 200228B: Swift detection of a burst
Date
2020-02-28T11:27:30Z (4 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
S. Laha (GSFC/UMBC/CRESST), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), C. Gronwall (PSU), J.D. Gropp (PSU) and
K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 11:14:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200228B (trigger=958733).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 252.026, +16.960, which is 
   RA(J2000)  =  16h 48m 06s
   Dec(J2000) = +16d 57' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 25 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 11:16:56.8 UT, 135.7 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 252.04730, 16.98505 which is equivalent
to:
   RA(J2000)  = 16h 48m 11.35s
   Dec(J2000) = +16d 59' 06.2"
with an uncertainty of 5.7 arcseconds (radius, 90% containment). This
location is 116 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. No spectrum from the promptly downlinked
event data is yet available to determine the column density. 

UVOT data are unavailable at this time. 

Burst Advocate for this burst is S. Laha (sib.laha AT gmail.com). 
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/)
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