[vsnet-grb-info 8256] GRB 090813: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9781
SUBJECT: GRB 090813: Swift detection of a burst
DATE:    09/08/13 04:26:12 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

J. R. Cummings (NASA/UMBC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
C. Gronwall (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:

At 04:10:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090813 (trigger=359884).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 227.017, +88.573 which is 
   RA(J2000) = 15h 08m 04s
   Dec(J2000) = +88d 34' 21"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a duration of about 8 sec.  The peak count rate
was ~9000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 04:12:01.7 UT, 78.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 225.8016, +88.5687 which is equivalent to:
   RA(J2000)  = 15h 03m 12.38s
   Dec(J2000) = +88d 34' 07.3"
with an uncertainty of 6.1 arcseconds (radius, 90% containment). This
location is 110 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. 

The initial flux in the 2.5 s image was 6.26e-10 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 87 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
0.17. 




Burst Advocate for this burst is J. R. Cummings (jayc AT milkyway.gsfc.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.)