GCN Circular 28211

E. Ambrosi (INAF-IASFPA), D. N. Burrows (PSU), V. D'Elia (SSDC),
J.D. Gropp (PSU), H. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), M. J. Moss (GWU),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 15:28:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 200806A (trigger=987016).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 52.905, +37.082 which is 
   RA(J2000) = 03h 31m 37s
   Dec(J2000) = +37d 04' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty). The BAT light curve showed a pulse 
that starts at ~T0 and lasts beyond the currently available data,
which ends at ~T+8 s. The peak count rate was ~4800 counts/sec (15-350 keV), 
at ~0 sec after the trigger. 

The XRT began observing the field at 15:30:07.6 UT, 77.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 52.93173, 37.07845
which is equivalent to:
   RA(J2000)  = 03h 31m 43.62s
   Dec(J2000) = +37d 04' 42.4"
with an uncertainty of 3.5 arcseconds (radius, 90% containment). This
location is 77 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 2.56
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 2.59e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 86 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 typical 3-sigma upper limit has been about 19.6 mag. 
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
0.42. 

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/)