GCN Circular 9280

C. B. Markwardt (CRESST/GSFC/UMD), S. D. Barthelmy (GSFC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
B. A. Rowlinson (U Leicester), M. H. Siegel (PSU),
M. Stamatikos (NASA/ORAU) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 04:53:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090429 (trigger=350853).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 90.559, -52.386 which is 
   RA(J2000) = 06h 02m 14s
   Dec(J2000) = -52d 23' 09"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a broad peak
with a duration of about 25 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 04:54:38.0 UT, 58.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 90.5548, -52.3855 which is equivalent to:
   RA(J2000)  = 06h 02m 13.15s
   Dec(J2000) = -52d 23' 07.8"
with an uncertainty of 5.1 arcseconds (radius, 90% containment). This
location is 9.4 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 150 seconds with the White filter
starting 66 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 100% of
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
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
0.06. 




Because this burst was detected as part of the sub-threshold program
(see GCN 8943
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 ) with a BAT image significance of only 5.64 sigma,
GCN notices were not generated until the source was confirmed
using XRT data. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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: http://www.swift.psu.edu/too.html.)