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GCN Circular 9281

GRB 090429B: Swift detection of a burst
2009-04-29T05:47:53Z (15 years ago)
David Palmer at LANL <>
T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), B. A. Rowlinson (U Leicester),
M. H. Siegel (PSU), M. Stamatikos (NASA/ORAU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 05:30:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090429B (trigger=350854).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 210.704, +32.163 which is 
   RA(J2000) = 14h 02m 49s
   Dec(J2000) = +32d 09' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed three peaks
with a duration of about 5 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 05:31:50.0 UT, 106.6 seconds after
the BAT trigger. Using promptly downlinked data we find an
uncatalogued X-ray source with an enhanced position: RA, Dec 210.6670,
32.1707 which is equivalent to:
   RA(J2000)  = 14h 02m 40.09s
   Dec(J2000) = +32d 10' 14.6"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 116 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 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.2e+20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 99 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 but does not 
overlap the XRT 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 and 100% of
the XRT 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  0.01. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT 
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:
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