TITLE:   GCN CIRCULAR
NUMBER:  23615
SUBJECT: GRB 190106A: Swift detection of a burst with an optical counterpart
DATE:    19/01/06 13:45:24 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

E. Sonbas (Adiyaman Univ.), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU), C. Gronwall (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC) and
K. L. Page (U Leicester) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 13:34:44 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190106A (trigger=882252).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 29.886, +23.857, which is 
   RA(J2000)  =  01h 59m 33s
   Dec(J2000) = +23d 51' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 100 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~10 sec after the trigger. 

The XRT began observing the field at 13:36:06.3 UT, 81.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 29.87964, 23.84516 which
is equivalent to:
   RA(J2000)  = 01h 59m 31.11s
   Dec(J2000) = +23d 50' 42.6"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 47 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 0.1 s image was 1.98e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 90 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	01:59:31.18 =  29.87993
  DEC(J2000) = +23:50:44.0  =  23.84555
with a 90%-confidence error radius of about 0.61 arc sec. This position is 5.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.45 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.09. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.com). 
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.)