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GCN Circular 8795

Subject
GRB 090111: Swift detection of a burst
Date
2009-01-12T00:15:21Z (15 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
T. Sakamoto (NASA/UMBC), M. M. Chester (PSU), E. A. Hoversten (PSU),
H. A. Krimm (CRESST/GSFC/USRA), J. Mao (INAF-OAB),
R. Margutti (Univ Bicocca&OAB), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 23:58:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090111 (trigger=339696).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 251.645, +0.091 which is 
   RA(J2000) = 16h 46m 35s
   Dec(J2000) = +00d 05' 28"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 30 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 23:59:38.3 UT, 76.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
variable, uncatalogued X-ray source with an enhanced position: RA, Dec
251.6759, 0.0769 which is equivalent to:
   RA(J2000)  = 16h 46m 42.21s
   Dec(J2000) = +00d 04' 36.8"
with an uncertainty of 3.0 arcseconds (radius, 90% containment). This
location is 122 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
6.45e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 3.05e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 86 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 3-sigma
upper limit at the location of the XRT candidate is 19.3 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  0.16. 

Burst Advocate for this burst is T. Sakamoto (Taka.Sakamoto 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.)
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