GRB 081109

S. Immler (CRESST/GSFC/UMD), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 07:02:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081109 (trigger=334112).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 330.787, -54.719 which is 
   RA(J2000) = 22h 03m 09s
   Dec(J2000) = -54d 43' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a triangular
structure with a duration of about 40 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at 20 sec after the trigger. 

The XRT began observing the field at 07:03:12.2 UT, 65.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 330.7911, -54.7114 which is equivalent to:
   RA(J2000)  = 22h 03m 09.86s
   Dec(J2000) = -54d 42' 41.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 28 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 4.78e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. 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 0.02. No afterglow candidate has been detected. 

Burst Advocate for this burst is S. Immler (immler 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.)

P. D'Avanzo, S. Covino, L.A. Antonelli, D. Malesani, D. Fugazza, L.  
Calzoletti,  S. Campana, G. Chincarini, M.L. Conciatore, S. Cutini,  
V. D'Elia,  F. D'Alessio, F. Fiore, P. Goldoni, D. Guetta,  C.  
Guidorzi, G.L. Israel, E. Maiorano, N. Masetti, A. Melandri, E.J.A.  
Meurs, L. Nicastro, E. Palazzi, E. Pian, S. Piranomonte, L. Stella,  
G. Stratta, G. Tagliaferri, G. Tosti, V. Testa, S.D. Vergani, F.  
Vitali report on behalf of the REM team:

The robotic 60-cm REM telescope located at La Silla (Chile) observed  
automatically the field of the GRB 081109 (Immler et al. GCN 8500
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 ) on  
Nov 09 starting about 52 s after the burst.  Observations were  
carried out at high airmass (~ 6). We clearly detect an object in our  
first K-band image inside the XRT error box (Immler et al. GCN 8500
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 )  
at the following coordinates (J2000):

R.A. = 22:03:09.72
Dec = -54:42:39.5

with an uncertainty of 1.0". The object is not visible in the single  
RJH images taken approximately at the same epoch. Coadding all the  
available RJH images taken around the same epoch we obtain the  
following results:

Mean_obs         texp   #frames_coadd    Filter    Mag

Nov 09.30604 UT  780 s     11   R    > 16.5 (3sigma)
Nov 09.30707 UT   65 s      4    J    > 15.8 (3sigma)
Nov 09.29936 UT   75 s      7    H    15.47 � 0.26
Nov 09.30145 UT   10 s      1    K    14.51 � 0.27

The object subsequently brightened, reaching K = 14.27 � 0.16 on Nov  
09.30612 UT. No object is detected at this position in the 2MASS and  
USNO catalogs. We propose this is the NIR afterglow of GRB 081109. We  
cannot indeed exclude the possibility that the lack of detection  
blueward of the H band is due to an high-redshift nature of this  
event. We note, however, that the large airmass badly affects the  
images in the J and R bands, so that our limits are not very  
constraining

Further deep optical/NIR observations are encouraged.

N. P. M. Kuin (MSSL/UCL) and S. Immler (CRESST/GSFC/UMD)
report on behalf of the Swift UVOT team.

The Swift UltraViolet/Optical Telescope (UVOT) began observing
GRB 081109 (Swift BAT trigger number 334112; Immler et al.,
GCN Circ. 8500
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 ) on November 9, 2008, with a white filter finding
chart at 07:03:23 UT, 75 seconds after the trigger.

No new source is detected in any of our images at the position
consistent with the reported XRT position in GCN Circ. 8500
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 .

The magnitudes and upper limits for GRB081109 at this position
are given below:

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

wh      75       6592     745      >21.49  (3-sigma UL)
u      287       6181     501      >20.57  (3-sigma UL)
b      543       6387     452      >20.35  (3-sigma UL)
uvw2   593       5362     274      >20.03  (3-sigma UL)
v      617       5566     274      >19.09  (3-sigma UL)
uvm2   641       5771     274      >19.87  (3-sigma UL)
uvw1   666       5976     255      >20.00  (3-sigma UL)

The values quoted above are on the UVOT Photometric System
(Poole et al, 2008, MNRAS 383, 627). They are not corrected for
the expected galactic reddening of E(B-V) = 0.019 in the direction
of the burst (Schlegel et al. 1998).

A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: 

"At 07:02:02.42 UT on 09 November 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081109 (trigger 247906923 / 081109293), which was 
also detected by the SWIFT (S. Immler et al. 2008, GCN 8500
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 ).
The GBM on-ground location is consistent with the Swift position.

The GBM light curve shows a single peak
with a duration (T90) of about 45 s (8-1000 keV). 
The time-averaged spectrum from T0-6.144 s to T0+26.624 s is 
best fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.28 +/- 0.09 and
the cutoff energy, parameterized as Epeak is 240 +/- 60 keV.
(chi squared 510 for 478 d.o.f.)
The event fluence (8-1000 keV) in this time interval is 
(6.53 +/- 0.43)E-06 erg/cm^2. The 1-sec photon flux measured 
starting from T0+9.216 s in the 8-1000 keV band 
is  3.2 +/- 0.3  ph/s/cm^2.

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

C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) and G. Szokoly 
(Eoetvoes Univ., Budapest and MPE) report on behalf of the GROND team:

We observed the field of GRB 081109 (Swift trigger #334112; Immler et al., GCN 
#8500
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 ) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 
120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla Observatory 
(Chile).
 
Observations started at 00:08 UT on November 10th, 2008, 17.1 hr after the GRB 
trigger, and are continuing. They were performed during astronomical twilight 
at an average seeing of 1.0" and at an average airmass of 1.1 as well as 
under bright Moon.
 
Based on the first 7.7 min of total exposures in g'r'i'z' and 8.0 min in JHK, 
we detect the afterglow candidate reported by D'Avanzo et al. (GCN #8501
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 ) and 
estimate preliminary magnitudes (all in AB system) of
 
g' > 22.8
r' ~ 22.8 +/- 0.3
i' ~ 21.8 +/- 0.15
z' ~ 21.4 +/- 0.15
J ~ 20.4 +/- 0.10
H ~ 19.7 +/- 0.15
K ~ 18.9 +/- 0.20
 
These magnitudes are calibrated against GROND zeropoints as well as 
2MASS field stars.
 
The spectral energy distribution is very red, and requires an extinction
of A_V > 0.5. With this strong extinction, and our g'-band limit being
compromised by the nearby full Moon, we cannot derive a redshift
at this stage.

C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) report on
behalf of the GROND team:

We report on further analysis of the GROND data of GRB 081109 detected
by Swift (trigger 334112; Immler et al., GCN #8500
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 ) and Fermi/GBM
(von Kienlin 2008, GCN #8505
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 ) taken simultaneously in g'r'i'z'JHK.

In a combined 2~h exposure at a midtime of 18.5~hours after the burst, 
we clearly detect the afterglow reported by D'Avanzo et al. (GCN 
#8501
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 ) and Clemens et al. (GCN #8510
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 ) in all filters.

Using 2MASS field stars in JHK and the GROND zeropoints in g'r'i'z' we 
estimate preliminary AB magnitudes of

g' = 23.14 +- 0.18 mag,
r' = 22.55 +- 0.15 mag,
i' = 22.00 +- 0.16 mag,
z' = 21.54 +- 0.15 mag,
J  = 20.49 +- 0.07 mag,
H  = 19.56 +- 0.06 mag and
K  = 18.84 +- 0.10 mag

which have been corrected for the expected Galactic reddening of 
E_(B-V)=0.02 (Schlegel et al. 1998).

Assuming Ly-alpha absorption, the g' band detection implies a redshift 
of z < 3.5.

The Galactic foreground corrected broad band SED is best fit with a 
power law template and significant extinction in the host. Depending 
on the used model, the  best fit intrinsic extinction A_V^{host} 
varies between 0.6 and 1.2. We caution however, that this is strongly 
dependent on the unknown redshift and subject to changes due to an
future improved calibration.

Klotz, A. (CESR-OMP), Gendre B. (LAM-OAMP),
Boer M. (OHP-OAMP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 081109 detected by SWIFT
(trigger 334112) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 29.4s after the GRB trigger.
The elevation of the field decreased from
11 degrees above horizon and weather conditions
were excellents.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect the afterglow mentioned by D'Avanzo et
al. (GCNC 8501) with a limiting magnitude of:

t0+29.4s to t0+89.4s : R > 16.9

This image was taken during the gamma emission.
This means that there was no bright optical flash
associated to this burst.

The second image is 30.0s exposure in tracking mode.
We detect the afterglow:

t0+95.1s to t0+125.1s : R ~ 17.8 +/- 0.2

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

This message may be cited.

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 REM position of the GRB 081109 optical afterglow (GCN
8501
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 ) at 4.800 and 4.928 GHz with the Australia Telescope Compact Array
(ATCA) between 01:15:05 UT, November 24, 2008 and 20:35:30 UT, November
25, 2008.

We did not detect a radio source at the optical afterglow position of
the GRB 081109 (GCN 8501
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 ). The data at 4.800 and 4.928 GHz were merged
and the radio flux density at the afterglow position found out to be 25
+/- 92 uJy/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/grb081109_field_image