GRB 081104

A. M. Parsons (GSFC), A. P. Beardmore (U Leicester),
P. J. Brown (PSU), P. A. Evans (U Leicester), C. Gronwall (PSU),
C. Guidorzi (INAF-OAB), S. T. Holland (CRESST/USRA/GSFC),
N. P. M. Kuin (MSSL), V. La Parola (INAF-IASFPA),
V. Mangano (INAF-IASFPA), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
K. L. Page (U Leicester), P. Romano (INAF-IASFPA),
T. N. Ukwatta (GSFC/GWU) and H. Ziaeepour (UCL-MSSL) report on behalf
of the Swift Team:

At 09:34:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081104 (trigger=333666).  
The BAT on-board calculated location is 
RA, Dec 100.485, -54.732 which is 
   RA(J2000) = 06h 41m 56s
   Dec(J2000) = -54d 43' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple peaked
structure with a duration of about 30 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~10 sec after the trigger. 

Due to an observing constraint, Swift will not slew until 
T0+40.5 minutes. There will be no XRT or UVOT data until
this time. 

Burst Advocate for this burst is A. M. Parsons (parsons 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.)

V. Mangano, V. La Parola (INAF-IASF PA), P. Evans (U. Leicester)
report on behalf the Swift XRT Team:


Swift slewed to the target (trigger=333666, Parsons et al.,
GCN Circ. 8473
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 ) at about 10:14:00 UT.
Using promptly downlinked XRT data we find an uncatalogued
source located at RA,Dec = 100.4835, -54.7211
which is equivalent to:

RA  (J2000.0) =  06 41 56.04
DEC (J2000.0) =  -54 43 15.9

with an uncertainty of 4.04 arcsec (radius, 90% containment).
This location is 39.4 arcsec from the BAT position, inside the BAT
error circle.

This is an official product of the Swift XRT Team.

A. Melandri, D.F. Bersier, M. Burgdorf, C.G. Mundell, R.J. Smith,
I.A. Steele (Liverpool JMU) on behalf of a larger collaboration
report:


On 2008 November 04 on 12:13 UT we observed the field of GRB 081104
(trigger = 333666, Parsons et al., GCN 8473
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 ) with the robotic 2m
Faulkes Telescope South located in Australia.

We do not detect any fadind optical source within the XRT error circle
(Mangano et al., GCN 8474
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 ) down to the following limit:


   Dt_mid    T_exp     Filter      Mag_lim
    [hr]     [min]
===========================================
    2.89     30.0        R         > 21.9
===========================================


Limiting magnitude has been estimated using the R2 magnitude of the
USNO-B1 catalogue. The reported value is not corrected for the
Galactic extinction.

P. J. Brown, C. A. Swenson (PSU), S. T. Holland, and A. M. Parsons (GSFC),
on behalf of the Swift/UVOT team.

The Swift Ultra-Violet/Optical Telescope (UVOT) began settled
observations of GRB 081104 (trigger 333666) 2638 seconds after the BAT
trigger (Parsons et al., GCN Circ. 8473
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 ). No afterglow is detected at the
XRT position (Mangano et al., GCN Circ. 8474
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 ) in any filter.
The limiting magnitudes (3-sigma in 5" radius apertures) in each
of the UVOT filters are as follows:

Filter  T_start(s)  T_stop(s)  Exp(s)  Mag UL (3sig)

white     2638      3882       209     >21.1
v         2794      9582       1082    >20.5
b         3614      3814       197     >20.4
u         3409      3609       197     >20.1
uvw1      3204      3404       197     >19.8
uvm2      2999      9874       479     >20.1
uvw2      2788      5368       197     >19.9

The values quoted above are in the UVOT photometric system (Poole et al.
2008, MNRAS, 383, 627).  They are not corrected for the expected
Galactic extinction corresponding to a reddening of E(B-V)=0.11 mag in
the direction of the burst (Schlegel et al. 1998).

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC),C. B. Markwardt (GSFC/UMD),
K. McLean (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC),
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-240 to T+962 sec from the recent telemetry
downlink,
we report further analysis of BAT GRB 081104 (trigger #333666)
(Parsons, et al., GCN Circ. 8473
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 ).  The BAT ground-calculated position is
RA, Dec = 100.500, -54.722 deg which is
   RA(J2000)  =  06h 42m 00.0s
   Dec(J2000) = -54d 43' 17.4"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.
 
The BAT mask-weighted light curve shows a single FRED peak.
T90 (15-350 keV) is 59.1 +- 13.9 sec (estimated error including
systematics).
 
The time-averaged spectrum from T-23.5 to T+51.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.00 +- 0.14.  The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-06
erg/cm2.
The 1-sec peak photon flux measured from T+13.54 sec in the 15-150 keV band
is 1.0 +- 0.3 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/333666/BA/

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

Using 4796 s of XRT Photon Counting mode data and 6 UVOT
images for GRB 081104, 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 = 100.4886, -54.7199 which is equivalent
to:

RA (J2000): 06h 41m 57.26s
Dec (J2000): -54d 43' 11.5"

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.

V. Mangano, V. La Parola, B. Sbarufatti (INAF-IASF PA)
report on behalf the Swift-XRT Team:

Swift XRT follow-up observation of the field of GRB 081104
(trigger=333666, Parsons et al., GCN Circ. 8473
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 ) started on
2008 11 04 at 10:18:45 UT (about 40 min after the trigger).

We have analysed the first four orbits of PC mode XRT data
accumulated from T+2640 s to T+22153 s (6.5 ks exposure).
The light curve of the X-ray source given in Mangano e. at,
GCN Circ. 8474
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  shows a power-law decay with slope -1.0 +/- 0.2,
with an initial count rate at the level of 0.1 counts/s.
If decaying at this rate the source will reach a count rate
level of 3.e-3 counts/s at T+24 hours.

The average spectrum of the source have been fitted with Cash
statistics. It can be modeled with a highly absorbed power law,
with NH=(1.5 +/ -0.4)e22 cm^-2 (significantly in excess with respect
to the Galactic absorption along the line of sight, of 7.0e20  cm^-2;
Kalberla et al. 2005) and a photon index of 5.2 +/- 1.0
(C-statistic=84.4 with 93 bins).


With the power law fit, the average observed (unabsorbed) flux
in the 0.3-10 keV energy range is of 8.0e-13 (1.9e-10) erg cm^-2 s^-1.

This is an official product of the Swift-XRT Team.

C. Clemens, T. Kruehler, J. Greiner, R. Filgas, A. Yoldas (all MPE Garching),
A. Kupcu Yoldas (ESO) and G. Szokoly (Eoetvoes Univ., Budapest) 
report on behalf of the GROND team:
 
We observed the field of GRB 081104 (Swift trigger 333666; Parsons et al., GCN
#8473
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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 07:43 UT on November 5th, 2008, 22.1 hr after the GRB
trigger. They were performed at an average seeing of 1.0" and at an average
airmass of 1.1.

We found a single point source at the edge of the astrometrically 
corrected 1.6'' Swift-XRT error circle reported by Beardmore et al. 
(GCN #8480
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 ) at
  
RA (J2000.0) = 06h 41m 57.13s  
DEC (J2000.0) = -54d 43' 09.9''
  
with an uncertainty of 0.5".
  
Based on the first 25 min of total exposures in g'r'i'z' and 20 min in
JHK, we estimate preliminary magnitudes (all in AB system) of
  
g' ~ 22.7 mag, 
r' ~ 22.6 mag, 
i' ~ 21.8 mag, 
z' ~ 21.7 mag, 
J ~ 21.2 mag,
H > 21.1 mag and
K > 20.0 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)= 0.1
  
The extinction-corrected spectral energy distribution is only marginally
consistent with a power law, so at present (without proper calibration)
we cannot distinguish between a foreground star, an afterglow, or a host.
No statement about variability can be made at this point either. 

We note that a very faint object is also visible on the POSS-IIN plate at 
this location.

C. Clemens, T. Kruehler, J. Greiner (all MPE Garching) and G. Szokoly 
(Eoetvoes Univ., Budapest) report on behalf of the GROND team:
 
We observed the field of GRB 081104 for a second time at 04:29 UT on November 
6th, 2008, 42.9 hr after the GRB trigger with 73.0 min of total exposures in 
g'r'i'z' and 64.0 min in JHK. Observations were performed at an average 
seeing of 1.7".

We still detect the previously reported source (Clemens et al., GCN #8482
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 ) 
with magnitudes identical within the errors to our first epoch observations.

Therefore, this object is most likely not the afterglow of GRB 081104.

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 GROND position of the GRB 081104 optical afterglow (GCN
8482
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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 081104 (GCN 8482
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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
-0.142 +/- 0.152 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/grb081104_field_image