GRB 081118

Subject: GRB 081118: Zadko observations
From: D.M Coward at UWA


D.M. Coward, T. Vaalsta, J. Zadko, A. Imerito, D. Blair, R. Burman,  
P. Lucas, S. Gordon, K. Frost, A. Fletcher
(University of Western Australia)
M. Todd, M. Zadnik (Curtin University)
M. Boer, A. Klotz (TAROT)


On 18 Nov, the Zadko Telescope team observed the XRT field of GRB  
081118 reported by P. Evans (GCN 8525
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 ) using the 1 meter Zadko  
Telescope (in very early commissioning mode). Imaging commenced  
approx 1.96 hr post burst trigger using an unfiltered integrating CCD  
video camera and continued over a period of 1 hr.
  The OA candidate reported by GCN 8529
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  is seen in a selected stack  
of 40 x 5 second exposures, though it is near the detection limit.
  We do not have absolute standard star photometric calibration.
Using nearby USNO-B1 stars we estimate the limiting magnitude of the  
OA to be in the range 20.9 +- 0.5.

This message is quotable in publications.

David Coward and Timo Vaalsta report on behalf of the UWA Zadko  
Telescope Team.

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 VLT position of the GRB 081118 optical afterglow (GCN
8528
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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 081118 (GCN 8528
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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 -89
+/- 5.6 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/grb081118_field_image

P. N. Bhat (UAH), R. D. Preece (UAH) and A.J. van der Horst (NASA/ORAU)
report on behalf of the Fermi GBM Team:

At 21:00:53.53 UT on 18 November 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081118B (trigger 248734854 / 081118876).

The on-ground calculated location, using the GBM trigger
data, is RA = 54.0, DEC = -50.4 (J2000 degrees,
equivalent to 03 h 36 m, 50 d 24'), with an uncertainty
of 2.9 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which is currently estimated to be 2 to 3 degrees).

The angle from the Fermi LAT boresight is 41 degrees.

The GBM light curve consists of primarily 2 pulses.
It has a duration (T90) of about 20 s (8-1000 keV).
The time-averaged spectrum from T0-2.6 s to T0+27 s is
well fit by a Band function with Epeak = 41.2 +/- 3.9,
alpha = 0.8 +/- 0.5 and beta = -2.14 +/- 0.08.

The event fluence (8-1000 keV) in this time interval is
(1.12 +/- 0.61)E-7 erg/cm^2. The 1-sec peak photon flux
in the 8-1000 keV band is 0.67 +/- 0.37 ph/s/cm^2.

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

H.hayasi, N.Ohmori, K.Kono H.Tanaka, R.Hara, M.Yamauchi, E.Sonoda,
(University of Miyazaki)

We have observed the field covering the error circle of 
GRB081118(GCN 8524
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 , Hoversten et al.) 
with the unfiltered CCD camera on the 30-cm telescope at
University of Miyazaki.
The observation was started 14:57:54 UT, 38.1 min
after the Swift-BAT trigger time.

We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog.there is no new source
at the reported position.
(GCN 8524
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 , Hoversten et al. GCN 8526
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 , Palmer et al. GCN 8528
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 , D'Avanzo et al.) 


the upper limits are as follows:
--------------------------------------------------------------
Start(UT) End(UT) Num. of frames Limit (mag.)
--------------------------------------------------------------
15:35:58 15:36:28 1  16.7
15:35:58 16:11:50 32 17.6
---------------------------------------------------------------

Poonam Chandra (RMC) and Dale A. Frail (NRAO) report on
behalf of the Caltech-NRAO-Carnegie GRB Collaboration:

"We used the Very Large Array to observe the field of view toward
optically bright GRB 08118 (GCN 8524
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 ) at a frequency of 8.46 GHz
on 2008 Nov 20.35 UT. The GRB radio afterglow is undetected and
the peak radio flux at the ESO-VLT optical afterglow position 
(GCN 8528
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 ) is -70 � 60 uJy.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."

V. D'Elia (INAF-OAR),  C. C. Thoene (INAF-OAB), A. De Ugarte Postigo 
(ESO), P. D'Avanzo, S. Covino (INAF-OAB), S. Piranomonte (INAF-OAR), R. 
Salvaterra (INAF-OAB), G. Chincarini (Univ. Bicocca) report on behalf of 
the MISTICI collaboration:

We observed the optical afterglow candidate of GRB 081118 (D'Avanzo et 
al. GCN 8528
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 ; Loew et al. GCN 8529
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 ) with the ESO-VLT equipped with the 
FORS2 camera starting on Nov 19.1166 (about 12 hours after the burst) in 
spectroscopic mode. We took 2x30 min spectra covering the range 
4300-9000 Angstrom (based on a preliminary wavelength calibration) with 
a resolution of R=440.

We detect a broad absorption feature around lambda_obs = 4350 Angstrom. 
Interpreting this feature as Ly-alpha absorption the inferred redshift 
is z = 2.58. At this redshift we also detect the SiII (1260), SiII 
(1304), CII (1334), SiIV (1393,1402) doublet, SiII (1526), CIV 
(1548,1550) doublet, FeII (1608), AlII (1670), SiII (1808) and AlIII 
(1854).

We acknowledge support from the ESO staff.

L. Vetere, E. Hoversten (PSU) report on behalf of the Swift-XRT team.

The Swift-XRT started observing the field of GRB 081118 (trigger=334877,
Hoversten et al., GCN 8525
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 ) at 14:59:10.0 UT, 153.3 s after the BAT  
trigger.
The XRT observed the GRB in Windowed Timing (WT) mode until 216 s
after the trigger and Photon Counting (PC) mode thereafter.

The X-ray light curve from the first three orbits can be modelled with  
a broken
powerlaw with an initial rapid decay (slope of 4.8+/-1.0), a break  
time of 580 s,
followed by a shallower decay (slope of 0.6+/-0.3).

The spectrum of the WT data can be well fit by an absorbed powerlaw  
with a
photon index of 2.6 +/- 0.3 and an absorbing equivalent hydrogen column
density consistent with the Galactic one in the GRB direction (3.7e20  
cm^-2;
Kalberla et al.  2005). The observed (unabsorbed) 0.3-10 keV flux is  
1.79
(2.28) x 10^-10 erg cm^-2 s^-1.

The PC spectrum (T+250 s to T+19 ks) is best fit with a photon index of
2.5 +/- 0.3 and an absorbing equivalent hydrogen column density  
consistent
  with the Galactic one in the GRB direction (3.7e20 cm^-2; Kalberla  
et al.  2005).
The observed (unabsorbed) 0.3-10 keV flux over this interval is 7.6  
(9.4) x
10^-13 erg cm^-2 s^-1.

Assuming the X-ray emission from the burst continues to decline at the
same rate we predict an XRT count rate of 0.002 count s^-1 at T+24 hour,
or an observed 0.3-10 keV X-ray flux of 5.2 x 10^-14 erg cm^-2 s^-1.

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

S. Loew, J. Greiner, A. Yoldas (all MPE Garching), A. Kuepcue Yoldas (ESO), 
G. Szokoly (Eoetvoes Univ., Budapest, and MPE) report for the GROND team:

We observed the field of GRB 081118 (Swift trigger 334877; Hoversten et al., 
GCN #8524
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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 MPI/ESO telescope at La Silla Observatory
(Chile). Observations started at 00:35 UT on November 19th, 2008, 9.6 hr 
post-burst, when the GRB location was becoming visible at 20 degrees above 
horizon. Observations were performed at an average seeing of 1.0".

We detect the source reported by D'Avanzo et al. (GCN #8528
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 ) at the edge of 
the astrometrically corrected 2.0'' Swift-XRT error circle (Evans et al., 
GCN #8525
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 ). Based on a 20 min exposure at mid-time 1:55 UT, we estimate 
preliminary magnitudes (all in AB system) of

g' ~ 23.3 mag,     
r' ~ 23.0 mag,     
i' ~ 22.5 mag,     
z' ~ 22.0 mag,
J  ~ 21.6 mag,     
H  ~ 21.2 mag and  
K  ~ 20.6 mag      

with errors of +/- 0.2. These magnitudes are calibrated against GROND
zeropoints as well as 2MASS field stars, and are not corrected for the
galactic foreground extinction of E(B-V)= 0.04 (Schlegel et al. 1998).

The object clearly decayed by 0.6 mag over the course of 1.5 hrs, thus it 
is suggested as the couterpart of GRB 081118.

The spectral energy distribution is consistent with a power law, so the 
g'-band detection implies a redshift of this GRB smaller than 3.5.

P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-OAR), S. Covino (INAF-OAB), S. 
Piranomonte (INAF-OAR), R. Salvaterra (INAF-OAB), C. C. Thoene (INAF-OAB), 
G. Chincarini (Un. Bicocca) report on behalf of the MISTICI collaboration:

We observed the field of GRB 081118 (Hoversten et al. GCN 8524
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 ) with the 
ESO-VLT equipped with the FORS2 camera on Nov 19.0431 UT (about 10 hours 
after the burst). We detect an object in our R-band images at the edge 
of the refined XRT error box (Evans et al. GCN 8525
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 ). The object is 
around R ~ 22.5. At present it is not possible to say if it is variable 
or not. Object coordinates are (J2000):

R.A. = 05:30:22.18
Dec = -43:18:05.3

+/- 0.5". Further analysis is ongoing.

We acknowledge support from the ESO staff, in particular Antonio de 
Ugarte Postigo.

[GCN OPS NOTE(19nov08): Per author's request, "C. Thone" was changed
to "C. C. Thoene".]

E. A. Hoversten (PSU) reports on behalf of the Swift UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 081118 150s after the BAT trigger (Hoversten et al., GCN 8524
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 ).
We do not detect any source at the enhanced Swift XRT position (Evans
et al., GCN 8525
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 ).  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       150      300     147      > 21.32
white       854     1004     147      > 21.29
white      5726     5926     196      > 21.50
v          6137     6337     196      > 19.79
b          5522     5721     196      > 20.82
u          5316     5515     196      > 20.49
uvw1       5111     5310     196      > 20.26
uvm2       4905     5105     196      > 19.88
uvw2       5933     6132     196      > 20.24

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight of E_(B-V) = 0.04 mag.
All photometry is on the UVOT photometric system described in Poole et
al. (2008, MNRAS, 383, 627).

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
E. A. Hoversten (PSU), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 081118 (trigger #334877)
(Hoversten, et al., GCN Circ. 8524
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 ).  The BAT ground-calculated position is
RA, Dec = 82.572, -43.305 deg, which is 
   RA(J2000)  =  05h 30m 17.3s 
   Dec(J2000) = -43d 18' 16.2" 
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 61%.
 
The mask-weighted light curve shows a roughly symmetrical peak starting
at ~T+10 sec, peaking at ~T+25 sec, and ending at ~T+105 sec.
T90 (15-350 keV) is 67+- 28 sec (estimated error including systematics).
 
The time-averaged spectrum from T+19.6 to T+118.6 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.10 +- 0.16.  The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+46.97 sec in the 15-150 keV band
is 0.6 +- 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/334877/BA/

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

Using 4848 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 081118, 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 = 82.5928, -43.3009 which is equivalent
to:

RA (J2000): 05h 30m 22.28s
Dec (J2000): -43d 18' 03.1"

with an uncertainty of 2.0 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.

E. A. Hoversten (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
M. Capalbi (ASDC), P.A. Curran (MSSL-UCL), M. De Pasquale (UCL-MSSL),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
O. Godet (U Leicester), D. Grupe (PSU), C. Guidorzi (INAF-OAB),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
J. P. Osborne (U Leicester), C. Pagani (PSU), D. M. Palmer (LANL),
J. L. Racusin (PSU), P. Romano (INAF-IASFPA),
B. Sbarufatti (INAF-IASFPA), P. Schady (MSSL-UCL),
R. L. C. Starling (U Leicester), G. Tagliaferri (INAF-OAB),
E. Troja (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU)
report on behalf of the Swift Team:

At 14:56:36 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081118 (trigger=334877).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 82.590, -43.302 which is 
   RA(J2000)  =  05h 30m 22s
   Dec(J2000) = -43d 18' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Even though this is an image trigger,
there appears to be a peak of about 600 counts/sec starting 20 to 40 sec
after the start of the trigger integration. 

The XRT began observing the field at 14:59:10.0 UT, 153.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 82.59254, -43.30058 which
is equivalent to:
   RA(J2000)  = 05h 30m 22.21s
   Dec(J2000) = -43d 18' 02.1"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 8.4 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 consistent with the Galactic value of
3.74e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 6.01e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 164 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 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
0.04. 

Burst Advocate for this burst is E. A. Hoversten (hoversten AT astro.psu.edu). 
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.)