GRB 091109B

S. R. Oates (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
A. Rowlinson (U Leicester), T. Sakamoto (NASA/UMBC),
M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC), M. A. Stark (PSU),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 21:49:03 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 091109B (trigger=375409).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 112.717, -54.080 which is 
   RA(J2000)  =  07h 30m 52s
   Dec(J2000) = -54d 04' 48"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike
with a duration of about 0.4 sec.  The peak count rate
was ~30,000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 21:50:21.1 UT, 78.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 112.7349, -54.0896
which is equivalent to:
   RA(J2000)  = 07h 30m 56.39s
   Dec(J2000) = -54d 05' 22.7"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 51 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
9.23e+20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
296 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 3-sigma upper limit is 20.3 mag. The
coverage of the XRT error circle by the 8'x8' region for the list of sources
generated on-board is uncertain because the large number of sources filled the
available telemetry. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.17. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.ucl.ac.uk). 
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.)

B. E. Schaefer (Louisiana State), E.S. Rykoff (UCSB), T. Guver (U 
Arizona), H. Flewelling (IfA/Hawaii), S. B. Pandey (U Mich), report on 
behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 091109B (Swift trigger 375409; S. R. Oates et al., GCN 
10148
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 ), producing images beginning 9.4 s after the GCN notice time. An 
automated response took the first image at 21:49:24.5 UT, 21.6 s after the 
burst, under excellent conditions. We took 10 5-sec, 10 20-sec and 10 
60-sec exposures. These unfiltered images are calibrated relative to USNO 
A2.0 (R). Imaging is on going.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle or the XRT error circle, for both single 
images and coadding into sets of 10; the field is not crowded. Individual 
images have limiting magnitudes ranging from 15.9-17.0; we set the 
following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
21:49:24.5   21:49:29.5         5     16.0           21.6       N
21:49:24.4   21:50:40.5        76     16.9           21.5       Y

M. Jel����nek (IAA-CSIC), A. de Ugarte Postigo (INAF-OAB), R. Felletti, L.
Hanlon (UCD Dublin), H. Van Heerden (UOVS, Bloemfontein), P. Kub����nek
(IPL UV, IAA-CSIC) reports on behalf of a large collaboration:

Watcher telescope, located at Boyden Observatory, South Africa,
observed autonomously GRB 091109B (S. R. Oates et al., GCN 10148
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 ). We
obtained a set of 5s exposures in clear filter, starting 78s after the
GRB (65s after the notice). We see no new sources in the XRT error box
down to the single-image limiting magnitude of 16.5. Coaddition of
first 120s (mean exposure time 153s after the GRB) of imaging data
improves this limit to ~17.7 calibrated against field USNO-A2.0 R-band
stars. Those results are consistent with ROTSE-III non-detection
(Schaefer et al. GCN 10149
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 ).

We note that there is a R~15.3 galaxy 8" North-West of the XRT position,
posibly the host of this short GRB.

Further observations are ongoing. This message can be quoted.

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

Using 1173 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 091109B, 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 = 112.73603, -54.08983 which is equivalent
to:

RA (J2000): 07h 30m 56.65s
Dec (J2000): -54d 05' 23.4"

with an uncertainty of 2.8 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) and Evans
et al. (2009, MNRAS, 397, 1177).

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

C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
S. R. Oates (UCL-MSSL), 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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 091109B (trigger #375409)
(Oates, et al., GCN Circ. 10148
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 ).  The BAT ground-calculated position is
RA, Dec = 112.750, -54.092 deg which is
    RA(J2000)  =  07h 30m 59.9s
    Dec(J2000) = -54d 05' 30.6"
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 76%.

The mask-weighted light curve shows a single symmetrical peak of duration 0.32 
seconds.  There is no sign of extended emission.
T90 (15-350 keV) is 0.3 +- 0.03 sec (estimated error including systematics).

The time-averaged spectrum from T-0.0 to T+0.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.71 +- 0.13.  The fluence in the 15-150 keV band is 1.9 +- 0.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.33 sec in the 15-150 keV band
is 5.4 +- 0.4 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/375409/BA/

[GCN OPS NOTE(09nov09):  Per author's request, the "B" was added to the
GRB name and the reference was filled in.]

E. Berger (Harvard), K. Covey (Cornell), A. A. West, J. M. Andersen 
(BU), and M. McDonald (U. Maryland, College Park) report:

"We observed the XRT error circle (GCN #10151
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 ) of the short GRB 091109b 
(GCN #10152
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 ) with IMACS on the Magellan/Baade 6.5-m telescope starting 
on 2009 Nov. 10.167 UT (6.2 hours after the burst).  In a 1200-sec 
stacked R-band image we find no optical sources within the XRT error
circle to a 3-sigma limit of R~23 mag in comparison to several nearby 
stars in the USNO-B catalog.  We further note that the object claimed to 
be a galaxy north-west of the XRT position (GCN #10150
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 ) appears to be 
resolved into two point sources in our image (with a seeing of about
1.1 arcsec)."

A.J. Levan (Warwick), N.R. Tanvir (Leicester),  J. Hjorth, D. Malesani (DARK/NBI),
A. de Ugarte Postigo, P. D'Avanzo (INAF-OAB) report on behalf of a larger collaboration:

We observed the location of the short GRB 091109B (Oates et al. GCNC 10148), with
the VLT/FORS2. Observations began at 03:34 UT, approximately 5.7 hours after the burst.
Within the X-ray localisation (Evans et al. GCNC 10151)  we identify a faint source 
(Source A) at:

RA: 07:30:56.61
Dec: -54:05:22.85

We also identify a second, fainter source (Source B) just outside the X-ray localisation, 
at:

RA: 07:30:56.46
Dec: -54:05:25.56

Both positions have errors of ~0.5" in each axis.

Source A has R~25, and appears pointlike. At this stage we cannot make any claim of 
variability in either source A or B, although further observation are planned.

Additionally, we note that the apparently extended object to the NW is actually a blend
of two stars, and a possible galaxy, rather than a single object, and hence its relation
to GRB 091109B is currently unclear.

We thank P. Lyman and the staff of VLT for their assistance with these observations.

K.L. Page (U. Leicester) and S.R. Oates (UCL-MSSL) report on behalf of 
the Swift-XRT team:

We have analysed 9.7 ks of XRT data for GRB 091109B (Oates et al. GCN 
Circ. 10148
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 ), from 86 s to 22.9 ks after the BAT trigger. The data are 
entirely in Photon Counting (PC) mode. The enhanced XRT position for this 
burst was given by Evans et al. (GCN. Circ 10151).

The light curve can be modelled with a power-law decay with a decay index 
of alpha=0.62 (+0.11, -0.10). Although there is some evidence that there 
may be a steep, shallow, normal trend in the light-curve, as is often 
seen, there are not enough data points to warrant such additional 
modelling at this time.

A spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 2.0 (+0.5, -0.4). The 
best-fitting absorption column is 1.2 (+1.4, -0.1) x 10^21 cm^-2, in 
excess of the Galactic value of 9.2 x 10^20 cm^-2 (Kalberla et al. 2005). 
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor 
deduced from this spectrum is 3.8 x 10^-11 (5.3 x 10^-11) erg cm^-2 
count^-1.

If the light curve continues to decay with a power-law decay index of 
0.62, the count rate at T+24 hours will be 2.4 x 10^-3 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.1 x 10^-14 
(1.2 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at 
http://www.swift.ac.uk/xrt_products/00375409.

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

D. Malesani (DARK/NBI), A. de Ugarte Postigo (INAF/OABr), A. J. Levan 
(Univ. Warwick), N. R. Tanvir (Univ. Leicester), J. Hjorth (DARK/NBI), 
P. D'Avanzo (INAF/Brera), report on behalf of a larger collaboration:

Following the observations of GRB 091109B (Oates et al., GCN 10148
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 ) with 
the VLT reported by Levan et al. (GCN 10154
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 ), we obtained a further 
epoch of R-band imaging with mean time Nov 10.33 UT (10.22 hr after the 
burst), using the same instrument and configuration.

Source "A" by Levan et al. (GCN 10154
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 ) is still detected, and decayed by 
1.0+-0.3 mag during this time interval, implying a decay index of alpha 
= 1.7+-0.5. We hence conclude that the source is indeed the afterglow of 
GRB 091109B.

We acknowledge excellent support from the ESO staff at Paranal, in 
particular Alain Smette and Paul Lynam.

S. R. Oates (MSSL-UCL) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 091109B 84s after the BAT trigger (Oates et al., GCN 10148
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 ).
We do not detect any source at the enhanced Swift XRT position
(Evans et al. GCN 10151
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 ) and at the location of source A detected
by the VLT (Levan et al. GCN 10154
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 , Malesani et al. GCN 10156
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 )

The 3-sigma upper limits for the finding chart exposures (FC)
and summed images are:

Filter   T_start   T_stop   Exp(s)  Mag (3-sigma upper limit)
-------------------------------------------------------------
white (FC)  84     234       147         > 21.25
u     (FC)  296    546       246         > 20.29
white       577    18629     1313        > 22.09
v           627    11274     1172        > 20.96
b           553    17890     1337        > 21.78
u           701    23171     1761        > 21.61
uvw1        677    22710     1988        > 21.44
uvm2        652    12179     1160        > 20.87
uvw2        603    7050      471         > 20.52
-------------------------------------------------------------

The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight of E_(B-V) = 0.17 mag.
All photometry is on the UVOT photometric system described in Poole et
al. (2008, MNRAS, 383, 627).

M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
K. Yamaoka (Aoyama Gakuin U.), S. Sugita (Nagoya U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
N. Ohmori, E. Sonoda, K. Kono, H. Hayashi, A. Daikyuji,
Y. Nishioka, K. Noda, M. Yamauchi (Univ. of Miyazaki),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda,
T. Sugasahara (Saitama U.), Y. Urata, H.M Lin (NCU),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo),
on behalf of the Suzaku WAM team, report:


The short GRB 091109B (Swift/BAT trigger #375409 ; Oates et al., GCN  
10148
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 )
triggered the Suzaku Wide-band  All-sky Monitor (WAM) which covers an
  energy range of 50 keV - 5 MeV at 2009-11-09 21:49:02.83 UT (=T0).

The observed light curve shows a single peak starting at T0+0.3s, ending
  at T0+0.6s with a duration (T90) of about 0.19 seconds.
The fluence in 100 - 1000 keV was 9.98(-3.69,+0.72) x 10^-7 erg/cm^2.
  The 1-s peak flux measured from T0 was 1.75(-0.59,+0.14) photons/ 
cm^2/s
in the same energy range.

Preliminary result shows that the time-averaged spectrum from
T0s to T0+1s is well fitted by a power-law with exponential cutoff  
model:
   dN/dE ~  E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
   alpha       0.91(-0.78,+0.42), and
   Epeak       1330(-610,+1120) keV (chi^2/d.o.f. = 24.6/24).

All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.

The light curves for this burst are available at:

  http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html