GCN Circular 22682

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

At 19:46:13 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180504A (trigger=830822).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 331.134, -14.655 which is 
   RA(J2000) = 22h 04m 32s
   Dec(J2000) = -14d 39' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 50 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

Using promptly downlinked data we find a bright, uncatalogued X-ray
source located at RA, Dec 331.14235, -14.65988 which is equivalent to:
   RA(J2000)  = 22h 04m 34.16s
   Dec(J2000) = -14d 39' 35.6"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). 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 gives a column density consistent with the Galactic value of 3.50
x 10^20 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 9.57e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 117 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
0.04. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien AT nasa.gov). 
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.)