TITLE:   GCN CIRCULAR
NUMBER:  5743
SUBJECT: GRB 061021: Swift detection of a burst
DATE:    06/10/21 15:58:47 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

A. Moretti (INAF-OAB), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA),
J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD),
F. E. Marshall (NASA/GSFC), S. B. Pandey (UCL-MSSL),
A. M. Parsons (GSFC), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 15:39:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 061021 (trigger=234905).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 145.134, -21.928 {09h 40m 32s, -21d 55' 41"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
structure with a duration of about 12 sec.  The peak count rate
was ~12000 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 15:40:20 UT, 73 seconds after the
BAT trigger. XRT found a variable, uncatalogued X-ray source
located at RA(J2000) = 09h 40m 35.6s, Dec(J2000) = -21d 57' 05.3", with an
estimated uncertainty of 7.0 arcseconds (90% confidence radius). 
This location is 97 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
2.7e-09 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 80 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	09:40:36.12 = 145.1505
  DEC(J2000) = -21:57:05.4  = -21.9515
with a 1-sigma error radius of about 0.5 arc sec. This position is 6.7 arc sec. 
from the center of the XRT error circle. The estimated magnitude is 14.9 with a
1-sigma error of about 0.5 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.06.