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GCN Circular 33328

Subject
GRB 230216A: Swift detection of a burst
Date
2023-02-16T15:05:20Z (a year ago)
From
David Palmer at LANL <palmer@lanl.gov>
N. J. Klingler (GSFC/UMBC/CRESSTII), P. A. Evans (U Leicester),
R. A. J. Eyles-Ferris (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
T. M. Parsotan (GSFC/UMBC/CRESSTII), B. Sbarufatti (INAF-OAB) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 14:48:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230216A (trigger=1154815).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 113.966, -8.015 which is 
   RA(J2000) = 07h 35m 52s
   Dec(J2000) = -08d 00' 53"
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 20 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 14:50:15.1 UT, 100.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 113.95924, -8.01160
which is equivalent to:
   RA(J2000)  = 07h 35m 50.22s
   Dec(J2000) = -08d 00' 41.8"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 27 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.  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 3.17
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 105 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
0.197. 

The XRT position is 3.8" from the galaxy WISEA J073550.15-080045.2

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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/)
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