TITLE:   GCN CIRCULAR
NUMBER:  23830
SUBJECT: GRB 190202A: Swift detection of a burst with an optical counterpart
DATE:    19/02/02 01:58:11 GMT
FROM:    Aaron Tohuvavohu at PSU/Swift  <aaronb@swift.psu.edu>

A. Y. Lien (GSFC/UMBC), P. D'Avanzo (INAF-OAB), J.D. Gropp (PSU),
N. J. Klingler (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU)
and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 01:39:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 190202A (trigger=887217).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 166.512, +9.388 which is 
   RA(J2000) = 11h 06m 03s
   Dec(J2000) = +09d 23' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 30 sec.  The peak count rate
was ~4500 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 01:42:13.5 UT, 163.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 166.5026, 9.3779 which is equivalent to:
   RA(J2000)  = 11h 06m 0.62s
   Dec(J2000) = +09d 22' 40.4"
with an uncertainty of 5.9 arcseconds (radius, 90% containment). This
location is 49 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. 

UVOT took a finding chart exposure of 126 seconds with the White filter
starting 172 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	11:06:00.63 = 166.50262
  DEC(J2000) = +09:22:36.6  =	9.37683
with a 90%-confidence error radius of about 0.74 arc sec. This position is 3.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
16.01 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 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: /too.html.)