GCN Circular 23074

P. D'Avanzo (INAF-OAB), S. D. Barthelmy (GSFC),
S. W. K Emery (UCL-MSSL), N. P. M. Kuin (UCL-MSSL),
A. Y. Lien (GSFC/UMBC), A. Melandri (INAF-OAB),
M. J. Moss (George Washington University) and B. Sbarufatti (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 09:04:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180805A (trigger=851829).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 167.530, -45.331 which is 
   RA(J2000) = 11h 10m 07s
   Dec(J2000) = -45d 19' 50"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single-peaked
structure with a duration of about 1.5 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 09:06:15.1 UT, 86.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 167.5646, -45.3307
which is equivalent to:
   RA(J2000)  = 11h 10m 15.50s
   Dec(J2000) = -45d 19' 50.5"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 87 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.  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 1.68
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 89 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 0.19. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo 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/too.html.)