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GCN Circular 9935

Subject
GRB 090926B: Swift detection of a burst
Date
2009-09-26T22:20:28Z (14 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. Grupe (PSU), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC),
J. A. Kennea (PSU), P. T. O'Brien (U Leicester),
P. Romano (INAF-IASFPA), M. Stamatikos (OSU/NASA/GSFC),
M. A. Stark (PSU) and L. Vetere (PSU) report on behalf of the Swift
Team:

At 21:55:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090926B (trigger=370791).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 46.318, -39.011 which is 
   RA(J2000)  = 03h 05m 16s
   Dec(J2000) = -39d 00' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows  a single peak
with a duration of about 20 sec.  The peak count rate
was ~1600 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 21:57:16.8 UT, 88.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 46.30693,
-39.00545 which is equivalent to:
   RA(J2000)  = 03h 05m 13.66s
   Dec(J2000) = -39d 00' 19.6"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
position may be improved as more data are received; the latest position
is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.91e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 3.15e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 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
0.02. 

Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 
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.)
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