TITLE:   GCN CIRCULAR
NUMBER:  22335
SUBJECT: GRB 180115A: Swift detection of a burst with an optical counterpart. 
DATE:    18/01/15 04:27:22 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

J. K. Cannizzo (NASA/UMBC), J. R. Cummings (NASA/UMBC),
A. D'Ai (INAF-IASFPA), V. D'Elia (ASDC), A. Deich (PSU),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 04:16:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180115A (trigger=805318).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 12.073, -15.608 which is 
   RA(J2000) = 00h 48m 18s
   Dec(J2000) = -15d 36' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual for an image trigger, the
immediately available light curve shows no obvious variation. 

The XRT began observing the field at 04:18:14.7 UT, 131.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 12.03953, -15.62924 which
is equivalent to:
   RA(J2000)  = 00h 48m 09.49s
   Dec(J2000) = -15d 37' 45.3"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 138 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. No spectrum from the promptly downlinked
event data is yet available to determine the column density. 

The initial flux in the 2.5 s image was 3.57e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 140 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:48:09.25 =  12.03856
  DEC(J2000) = -15:37:49.8  = -15.63051
with a 90%-confidence error radius of about 0.75 arc sec. This position is 5.6
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.54 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.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.)