| Circular_text |
TITLE: GCN CIRCULAR
NUMBER: 8653
SUBJECT: GRB 081211: Swift detection of a burst
DATE: 08/12/11 12:16:45 GMT
FROM: Hans Krimm at NASA-GSFC
H. A. Krimm (CRESST/GSFC/USRA), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P.A. Curran (MSSL-UCL),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
O. Godet (U Leicester), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), S. D. Hunsberger (PSU),
N. P. M. Kuin (MSSL), V. Mangano (INAF-IASFPA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), A. M. Parsons (GSFC),
P. Romano (INAF-IASFPA), R. L. C. Starling (U Leicester),
T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf
of the Swift Team:
At 11:48:10 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081211 (trigger=337115). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 328.087, -33.815 which is
RA(J2000) = 21h 52m 21s
Dec(J2000) = -33d 48' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a weak
structure with a duration of about ~20 sec. The peak count rate
was ~400 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 11:50:00.6 UT, 109.9 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 328.1161, -33.8361
which is equivalent to:
RA(J2000) = 21h 52m 27.85s
Dec(J2000) = -33d 50' 09.8"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 115 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 (1.87e+20
cm^-2, Kalberla et al. 2005), with an excess column of 1.9
(+2.21/-1.92) x 10^21 cm^-2 (90% confidence).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 114 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 0.03.
Burst Advocate for this burst is H. A. Krimm (krimm 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.)
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