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GCN Circular 9718

Subject
GRB 090727: Swift detection of a burst
Date
2009-07-27T22:59:22Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
P. A. Evans (U Leicester), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. M. Chester (PSU), S. T. Holland (CRESST/USRA/GSFC),
N. P. M. Kuin (MSSL), C. B. Markwardt (CRESST/GSFC/UMD),
K. L. Page (U Leicester), A. Rowlinson (U Leicester),
M. H. Siegel (PSU), M. A. Stark (PSU) and T. N. Ukwatta (GSFC/GWU)
report on behalf of the Swift Team:

At 22:42:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090727 (trigger=358520).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 315.972, +64.916 which is 
   RA(J2000) = 21h 03m 53s
   Dec(J2000) = +64d 54' 58"
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 25 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 22:43:46.0 UT, 87.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 315.96139, 64.92438 which is equivalent
to:
   RA(J2000)  = 21h 03m 50.73s
   Dec(J2000) = +64d 55' 27.8"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 34 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 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
2.48e+21 cm^-2 (Kalberla et al. 2005). 


UVOT took a finding chart exposure of nominal 150 seconds with the White filter
starting 91 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. 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 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 0.54. 




Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.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.)
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