GRB 081211

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.)

A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 2165 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 081211, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 328.1163, -33.8364 which is equivalent
to:

RA (J2000): 21h 52m 27.91s
Dec (J2000): -33d 50' 10.9"

with an uncertainty of 1.6 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.

This circular was automatically generated, and is an official product of the
Swift-XRT team.

S. Immler (CRESST/UMD/GSFC), S. T. Holland (CRESST/USRA/GSFC), and H. A. 
Krimm (CRESST/GSFC/USRA) report on behalf of the Swift UVOT team:

Further analysis of Swift Ultraviolet/Optical Telescope (UVOT) data of 
GRB 081211 (Krimm et al., GCN Circ. 8653
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 ), starting 113 sec after the 
BAT trigger, gives a detection of an optical source within the enhanced 
Swift-XRT position (Beardmore et al., GCN Circ. 8655
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 ) at
     RA (J2000)  21:52:27.97 = 328.11654 (deg)
     Dec (J2000) -33:50:08.3 = -33.83565 (deg)
with an uncertainty of 0.7 arcseconds (radius, 90% containment) in the 
white filters at 4.5-sigma level of confidence. The source is not 
present in DSS, the USNO-B1.0 catalogue, or the 2MASS point source 
catalogue. It is not detected in any of the other UVOT filters at the 
limiting magnitudes reported below.

Filter Tstart(s) Tstop(s)  Exp(s)  Magnitude

wh     113       7134     588      21.23+/-0.39
u      326       6724     265      >20.23  (3-sigma UL)
b      582        741     293      >20.24  (3-sigma UL)
uvw2   632       7318     371      >20.40  (3-sigma UL)
v      656      11966     386      >19.38  (3-sigma UL)
uvm2   681       6314     136      >19.58  (3-sigma UL)
uvw1   706       6519     196      >19.87  (3-sigma UL)

The values quoted above are in the UVOT photometric system (Poole et al. 
2008, MNRAS, 383, 627) and are not corrected for the expected Galactic 
extinction along the line of sight which corresponds to a reddening of 
E(B-V)=0.077 mag (Schlegel et al. 1998).

R.L.C. Starling (U. Leicester) and H.A. Krimm (CRESST/GSFC/USRA) report on 
behalf of the Swift XRT team:

We have analysed data from the first 2 orbits of Swift XRT observations of 
GRB 081211 (trigger=337115, Krimm et al. GCN Circular 8653
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 ) from 113 s to 
24 ks after the BAT trigger, all collected in Photon Counting (PC) mode.

The enhanced Swift XRT position for this GRB is given in Beardmore et al. 
(GCN Circular 8655
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 ).

We confirm that the source is fading, however, the light curve is not well 
constrained at present. A power law fit results in a decay slope of 
alpha=0.6+/-0.1, but we note that flaring may be present from 350-1000 s.

The time-averaged spectrum can be fit with an absorbed power law with 
photon index Gamma=2.4+/-0.3. There is significant absorption above the 
Galactic value (nH_Gal=1.9e20 cm^-2, Kalberla et al. 2005) amounting to a 
column of nH=(1.2+/-0.6)e21 cm^-2 (at z=0). The observed (unabsorbed) 
0.3-10 keV flux is 3.1 (5.0) e-12 erg cm^-2 s^-1. The observed 
(unabsorbed) count rate to flux conversion derived from this spectrum is 1 
count s^-1 = 3.3 (5.3) e-11 erg cm^-2.
The predicted count rate at T+24h, assuming a decay of alpha=0.6, is 0.01
count s^-1.

The results of the XRT automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00337115.

This circular is an official product of the Swift-XRT team.

Using the data set from T-239 to T+963 sec from the recent telemetry 
downlink,
we report further analysis of BAT GRB 081211 (trigger #337115)
(Krimm, et al., GCN Circ. 8653
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 ).  The BAT ground-calculated position is
RA, Dec = 328.082, -33.818 deg which is
   RA(J2000)  =  21h 52m 19.7s
   Dec(J2000) = -33d 49' 05.9"
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 42%.
 
The mask-weighted light curve shows a single weak peak extending in time
from T-1 to T+3 seconds. There is a possible precursor at ~T-180 sec.
T90 (15-350 keV) is 3.5 +- 0.9 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.1 to T+2.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.34 +- 0.41.  The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-7 
erg/cm2.
The 1-sec peak photon flux measured from T+0.19 sec in the 15-150 keV band
is 0.8 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/337115/BA/