GRB 081226B

S.Mereghetti, A.Paizis (IASF-Milano), D.Gotz (CEA-Saclay), M.Turler,
V.Beckmann, M. Beck (ISDC, Versoix), and J. Borkowski (CAMK, Torun) on
behalf of the IBAS Localization Team report:

A short hard GRB consisting of a single peak with duration of  about 0.7 s 
has been detected by IBAS in IBIS/ISGRI data at 12:13:11 UT on December 26th. 

The refined coordinates (J2000)  are:

RA = 25.495 [degrees]
DEC= -47.439 [degrees]

with an uncertainty of 2.5 arcmin (90% c.l.).

A preliminary analysis gives a peak flux in the 20-200 keV range of  
about 3 ph/cmq/s (0.2 s integration time) and a fluence over the same energy
range of about 10e-7 erg/cmq.

A plot of the light curve will be posted at

http://ibas.iasf-milano.inaf.it/IBAS_Results.html

This message can be cited.

P.A. Evans (U. Leicester) and E.A. Hoversten (PSU) report on behalf of
the Swift team:

Swift observed the field of GRB 081226B (Mereghetti et al. GCN Circ
8734
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 ) for 8 ks, beginning 9.6 ks after the INTEGRAL trigger. The XRT
data (all in Photon Counting mode) contain no source in the INTEGRAL
error circle. A 3-sigma upper limit is 0.001 counts/sec which is 5.6e-14
erg cm^-2 s^-1 for a typical GRB spectrum.

Given the absence of an XRT position, the UVOT images were compared to
archival images from the Digitized Sky Survey.  No candidate afterglow
was found in the INTEGRAL error circle.  UVOT magnitude 3-sigma upper
limits are reported in the following table:

Filter   T_start   T_stop   Exp(s)  Mag (3-sigma upper limit)
-------------------------------------------------------------
WHITE     9744     22737    1414        > 22.24
v         9621     27619    1940        > 20.48
b         9720     21824    1414        > 21.06
u         9694     16082     352        > 20.34
uvw1     10019     15877     313        > 20.20
uvm2     15472     28224     787        > 20.75
uvw2     10812     23271     932        > 21.27

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight of E_(B-V) = 0.01 mag.
All photometry is on the UVOT photometric system described in Poole et
al. (2008, MNRAS, 383, 627).

This circular is an official product of the Swift XRT and UVOT teams.

E. Bissaldi (MPE) and S. McBreen (UCD/MPE)
report on behalf of the Fermi GBM Team: 


"At 12:13:10.71 UT on 26 December 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081226B (trigger 251986391 / 081226509),
which was also detected by INTEGRAL (Mereghetti et al. 2008, GCN 8734
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 )
The GBM on-ground location is consistent with the INTEGRAL position.
 
The angle from the Fermi LAT boresight is 22 degrees.

The GBM light curve consists of a single pulse
with a duration (T90) of about 0.35 s (8-1000 keV). 
The time-averaged spectrum from T0-0.08 s to T0+0.12 s is
well fit by a power law function with an exponential
high energy cutoff. The power law index is -0.51 +/- 0.17 and
the cutoff energy, parameterized as Epeak, is 530 +/- 110 keV
(chi squared 300 for 324 d.o.f.).
A Band function fits the spectrum equally well with
Epeak = 300 +/- 110 keV, alpha = -0.2 +/- 0.3 and
beta = -1.82 +/- 0.23 (chi squared 292 for 323 d.o.f.).

The event fluence (8-1000 keV) in this time interval for
the power law function with exponential cutoff is 
(6.1 +/- 0.5)E-07 erg/cm^2. The 64-ms peak photon flux
measured starting from T0-0.01 s in the 8-1000 keV band
is 17.7 +/- 1.5 ph/s/cm^2.


The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Steven Tingay (Curtin Institute of Radio Astronomy),
Chris Phillips (Australia Telescope National Facility), Gregory Taylor
(University of New Mexico), Mark Wieringa (Australia Telescope National
Facility) and Ralph Martin (Perth Observatory) report:

We observed the INTEGRAL-IBAS position of the GRB081226b (GCN 8734
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 ) at
4.800 and 4.928 GHz with the Australia Telescope Compact Array (ATCA)
between 01:00:00 UT and 22:00:00 UT on February 21/22, 2009.

We did not detect a radio source at the position of the GRB081226b (GCN
8734
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 ). The data at 4.800 and 4.928 GHz were merged and the radio flux
density at the GRB position found out to be -0.176 +/- 0.196 mJy/beam
(1-sigma).

The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.

See the 4.800 & 4.928 GHz combined image at:

http://cira.ivec.org/dokuwiki/doku.php/grb/grb081226b/grb081226b_field_image