TITLE:   GCN CIRCULAR
NUMBER:  22828
SUBJECT: GRB 180623A: Swift detection of a burst
DATE:    18/06/23 17:00:40 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
A. Deich (PSU), S. W. K Emery (UCL-MSSL), J.D. Gropp (PSU),
F. E. Marshall (NASA/GSFC) and D. M. Palmer (LANL) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 16:41:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180623A (trigger=844015).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 214.511, -60.294, which is 
   RA(J2000)  =  14h 18m 03s
   Dec(J2000) = -60d 17' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 4 large peaks and many
little peaks with a total duration of about 90 sec.  The peak count rate
was ~6500 counts/sec (15-350 keV), at ~61 sec after the trigger. 

The XRT began observing the field at 16:43:13.3 UT, 76.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 214.5295,
-60.2539 which is equivalent to:
   RA(J2000)  = 14h 18m 07.08s
   Dec(J2000) = -60d 15' 13.9"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 148 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
http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density. 

The initial flux in the 2.5 s image was 1.31e-08 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 85 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 8'x8'
region for the list of  sources generated on-board covers 100% of the
XRT error circle. The typical 3-sigma upper limit has been about 19.6
mag. The list of  sources is typically complete to about 18 mag. No
correction has been made for  the large, but uncertain, extinction
expected. 

Although this source is close to the Galactic plane (lat = 0.83 degrees), 
its distance from the Galactic center (46 degrees), the presence 
of significant flux above 100 keV, and the complexity and overall
shape of the lightcurve are consistent with a GRB that is aligned
with the plane due to random coincidence. 

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/too.html.)