TITLE:   GCN CIRCULAR
NUMBER:  9545
SUBJECT: GRB 090621B: Swift detection of a short hard burst
DATE:    09/06/21 22:38:35 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

P.A. Curran (MSSL-UCL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), A. Rowlinson (U Leicester),
T. Sakamoto (NASA/UMBC), P. Schady (MSSL-UCL), M. C. Stroh (PSU) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 22:07:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090621B (trigger=355359).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 313.432, +69.013 which is 
   RA(J2000)  =  20h 53m 44s
   Dec(J2000) = +69d 00' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration less than 128 millisec.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at  22:08:36UT, 70.7 s after the BAT trigger. 
In promptly downlinked data, XRT found a faint uncatalogued source at RA, Dec 
(J2000) = 313.4700,   69.0282, which is
RA = 20h 53m 52.8s
Dec = +69d 01' 41.5"
with an uncertainty of 8.0 arcseconds (radius, 90% containment). This
location is 73 arcseconds from the BAT onboard position, within the BAT
error circle. 

UVOT took a finding chart exposure of nominal 150 seconds with the
White filter  starting 76 seconds after the BAT trigger. No credible
afterglow candidate has  been found in the initial data products at
the XRT position. Data from the 2.7'x2.7' sub-image are not available
at this time. 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 expected extinction corresponding to E(B-V) of 0.43 (Schlegel et
al. 1998). 

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.)