GCN Circular 9540

P.A. Curran (MSSL-UCL), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU), M. C. Stroh (PSU),
T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf
of the Swift Team:

At 04:22:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090621 (trigger=355303).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 10.986, +61.968 which is 
   RA(J2000) = 00h 43m 57s
   Dec(J2000) = +61d 58' 04"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed weak emission during
the 8 seconds of the trigger interval.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~4 sec after the trigger. 

There was a second BAT trigger (trigger=355304) at 04:27:05, about 
4 minutes after the initial trigger from the same location.  This 
portion of the BAT light curve is not immediately available from 
TDRSS, but the retrigger could indicate an extended prompt phase. 

The XRT began observing the field at 04:24:40.46 UT, 117.3 seconds after
the BAT trigger. XRT found an uncatalogued, variable X-ray source located
at RA, Dec 11.0191, 61.9417 which is equivalent to:
   RA(J2000)  = 00h 44m 04.58s
   Dec(J2000) = +61d 56' 30.2"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 110 arcseconds from the BAT onboard position, within the BAT
error circle.  There is a bright peak at about 250s after the initial trigger
which could be X-ray emission during prolonged prompt emission. 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 122 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 25% of
the BAT 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
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected. 




Burst Advocate for this burst is P.A. Curran (pac AT mssl.ucl.ac.uk). 
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.)