GCN Circular 23201

V. D'Elia (SSDC), A. D'Ai (INAF-IASFPA), J.D. Gropp (PSU),
J. A. Kennea (PSU), M. J. Moss (George Washington University),
K. L. Page (U Leicester), D. M. Palmer (LANL) and B. Sbarufatti (PSU)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 13:57:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180905A (trigger=859421).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 91.035, -4.591 which is 
   RA(J2000) = 06h 04m 08s
   Dec(J2000) = -04d 35' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, no obvious
variation is visible in the immediately-available lightcurve. 

The XRT began observing the field at 14:00:12.3 UT, 145.9 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 91.0602, -4.5724 which is equivalent to:
   RA(J2000)  = 06h 04m 14.45s
   Dec(J2000) = -04d 34' 20.6"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 112 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 2.03e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 135 seconds with the White filter
starting 153 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
0.60. 

Burst Advocate for this burst is V. D'Elia (delia AT ssdc.asi.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.)