TITLE:   GCN CIRCULAR
NUMBER:  30250
SUBJECT: GRB 210618A: Swift detection of a burst
DATE:    21/06/18 02:09:20 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

M. G. Bernardini (INAF-OAB), P. D'Avanzo (INAF-OAB),
H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. Sbarrato (INAF-OAB)
and M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 01:43:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 210618A (trigger=1056426).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 235.820, +46.043 which is 
   RA(J2000) = 15h 43m 17s
   Dec(J2000) = +46d 02' 36"
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 3 sec.  The peak count rate
was ~3600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 01:44:42.2 UT, 65.3 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. Due to a short visibility interval, no further data were immediately 
collected. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

Due to the short visibility window, UVOT data are not available at this time. 

Burst Advocate for this burst is M. G. Bernardini (grazia.bernardini AT brera.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/)