[vsnet-grb-info 8387] GRB 090912: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9905
SUBJECT: GRB 090912: Swift detection of a burst
DATE:    09/09/12 16:15:11 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), K. L. Page (U Leicester),
P. Romano (INAF-IASFPA), T. Sakamoto (NASA/UMBC),
B. Sbarufatti (INAF-IASFPA), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 15:50:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090912 (trigger=362633).  Swift executed a delayed slewed
to the burst. 
The BAT on-board calculated location is 
RA, Dec 188.092, +61.513, which is 
   RA(J2000)  =  12h 32m 22s
   Dec(J2000) = +61d 30' 45"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks at T+0 and
at T+90 with a total duration of about 130 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 16:03:42.4 UT, 792.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 188.0422, 61.4843 which
is equivalent to:
   RA(J2000)  = 12h 32m 10.13s
   Dec(J2000) = +61d 29' 03.5"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 134 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 in excess of the Galactic value (1.28e+20
cm^-2, Kalberla et al. 2005), with an excess column of 6.2
(+4.43/-3.60) x 10^21 cm^-2 (90% confidence). 


UVOT took a finding chart exposure of 150 seconds with the White filter
starting 795 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 none of
the XRT error circle. 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 0.01. 




Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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.)