TITLE:   GCN CIRCULAR
NUMBER:  33271
SUBJECT: GRB 230205A: Swift detection of a burst
DATE:    23/02/05 11:01:42 GMT
FROM:    Elena Ambrosi at INAF-IASF  <elena.ambrosi@inaf.it>

E. Ambrosi (INAF-IASFPA), A. D'Ai (INAF-IASFPA), A. Y. Lien (U Tampa),
A. Melandri (INAF-OAB), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB)
and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 10:29:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230205A (trigger=1152764).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 202.072d, +46.684d which is 
   RA(J2000) = 13h 28m 17s
   Dec(J2000) = +46d 41' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a telemetry gap, the BAT light curve
before T+8s is not immediately available, and after that time shows 
no obvious variability.  The BAT rate trigger was on a 3 s timescale,
consistent with the lack of variation at later times. 

The XRT began observing the field at 10:31:40.0 UT, 108.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 202.07147, 46.72613
which is equivalent to:
   RA(J2000)  = 13h 28m 17.15s
   Dec(J2000) = +46d 43' 34.1"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 151 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 in excess of the Galactic value (2.09 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 1.2
(+0.71/-0.56) x 10^22 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 100 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 none of
the XRT error circle. 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 0.036. 

Burst Advocate for this burst is E. Ambrosi (elena.ambrosi 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/)