TITLE:   GCN CIRCULAR
NUMBER:  33989
SUBJECT: GRB 230618A: Swift detection of a burst
DATE:    23/06/18 04:09:22 GMT
FROM:    David Palmer at LANL <palmer@lanl.gov>


K. L. Page (U Leicester) and S. Laha (GSFC/UMBC) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 03:51:12 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230618A (trigger=1175438).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is   
RA, Dec 196.588, +3.306 which is 
   RA(J2000) = 13h 06m 21s
   Dec(J2000) = +03d 18' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a telemetry outage caused by
a recent storm in Guam, no further BAT data will be available
until a ground station pass. 

Using promptly downlinked data we find a bright, uncatalogued X-ray
source located at RA, Dec 196.60313, 3.30257 which is equivalent to:
   RA(J2000)  = 13h 06m 24.75s
   Dec(J2000) = +03d 18' 09.3"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). 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. 

The initial flux in the 2.5 s image was 6.46e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 137 seconds after the BAT trigger. No credible afterglow
candidate has been found in the initial data products. Data from the 2.7'x2.7'
sub-image are not available at this time. 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 0.025. 

Burst Advocate for this burst is K. L. Page (klp5 AT leicester.ac.uk). 
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/)