TITLE:   GCN CIRCULAR
NUMBER:  28043
SUBJECT: GRB 200630A: Swift detection of a burst
DATE:    20/06/30 02:09:43 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

K. L. Page (U Leicester), S. D. Barthelmy (GSFC), J.D. Gropp (PSU),
J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), M. J. Moss (GWU) and D. M. Palmer (LANL)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 01:49:34 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200630A (trigger=980210).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 91.380, -60.789 which is 
   RA(J2000) = 06h 05m 31s
   Dec(J2000) = -60d 47' 20"
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 10 sec.  The peak count rate
was ~1600 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 01:50:52.3 UT, 77.8 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 91.3308, -60.7524 which
is equivalent to:
   RA(J2000)  = 06h 05m 19.38s
   Dec(J2000) = -60d 45' 08.6"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 157 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 4.33
x 10^20 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 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 0.04. 

This burst is consistent with Fermi/GBM trigger number 615174580. 

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/)