GRB 091109

S. R. Oates (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC)
and L. Vetere (PSU) report on behalf of the Swift Team:

At 04:57:43 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 091109 (trigger=375246).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 309.265, -44.176 which is 
   RA(J2000) = 20h 37m 04s
   Dec(J2000) = -44d 10' 34"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a spiky
structure with a duration of about 25 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~20 sec after the trigger. 

The XRT began observing the field at 05:00:14.1 UT, 150.7 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 309.25854, -44.15853 which
is equivalent to:
   RA(J2000)  = 20h 37m 2.05s
   Dec(J2000) = -44d 09' 30.7"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 65 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 in excess of the Galactic value (2.99e+20
cm^-2, Kalberla et al. 2005), with an excess column of 3 (+1.84/-1.63)
x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 155 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	20:37:01.81 = 309.25755
  DEC(J2000) = -44:09:29.6  = -44.15821
with a 90%-confidence error radius of about 0.69 arc sec. This position is 2.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.92 with a 1-sigma error of about 0.18. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

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.)

L.A. Antonelli, S. Covino, P. D'Avanzo, 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 091109 (Oates et al. GCN10138
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 ) starting about
77 s after the burst. We detect a faint object in the XRT error circle in our
first H-band images at H~14.8 at coordinates: RA(J2000) 20:37:02.2; Dec(J2000)
-44:09:30.4 with 1 arcsec error.

This message can be cited"



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

Using 3018 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 091109, 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 = 309.25767, -44.15872 which is equivalent
to:

RA (J2000): 20h 37m 1.84s
Dec (J2000): -44d 09' 31.4"

with an uncertainty of 1.7 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.

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), 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-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 091109 (trigger #375246)
(Oates, et al., GCN Circ. 10138
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 ).  The BAT ground-calculated position is
RA, Dec = 309.252, -44.177 deg, which is 
   RA(J2000)  =  20h 37m 00.5s 
   Dec(J2000) = -44d 10' 36.0" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 19%.
 
The mask-weighted light curve shows a couple overlapping peaks. The first starts
at ~T-15 sec, peaks at ~T+10 sec.  The second (weaker) peaks at ~T+40 sec and
ends at ~T+60 sec.  T90 (15-350 keV) is 48 +- 17 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-0.8 to T+51.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.31 +- 0.25.  The fluence in the 15-150 keV band is 1.6 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+8.20 sec in the 15-150 keV band
is 1.3 +- 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/375246/BA/

C. Guidorzi (U. Ferrara), R.J. Smith, C.G. Mundell, D. Bersier,
A. Melandri, Z. Cano, S. Kobayashi, C.J. Mottram, I.A. Steele
(Liverpool JMU), A. Gomboc (U. Ljubljana) report on behalf of
a large collaboration:

On 2009 November 9 at 09:26:10 UT the 2-m Faulkes Telescope South
began observing GRB 091109 (Oates et al., GCN Circ. 10138
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 ) using
the R and i' filters.

We detect the UVOT optical afterglow candidate at a position
consistent with that reported by Oates et al. (but not consistent
with the object reported by REM Antonelli et al., GCN Circ. 10139
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 ),
with the following magnitudes:

Mid Time from GRB   Total Exp  Filter   Magnitude
(hours)             (s)
-----------------------------------------------------
4.74                600         i'      21.7  +- 0.3
5.29                600         R       21.95 +- 0.25
-----------------------------------------------------

Magnitudes have been calibrated from the nearby USNOB-1 star
20:37:02.508, -44:09:33.68, using R2=17.52 and I=17.61.

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

The Swift/UVOT began observerving the field of GRB 091109 156s
after the BAT trigger (Oates et al., GCN Circ. 10138
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 ). We detect the
optical afterglow in the white filter only, which faded rapidly.
The refined UVOT position is:

     RA (J2000)  20:37:01.80
    Dec (J2000) -44: 9:29.6

with an estimated uncertainty of 0.7 arcsec (radius, 90% confidence).
This position is consistent with the XRT refined position (Beardmore
et al., GCN Circ 10140
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 ).

Preliminary magnitudes and the 3 sigma upper limits are reported below.

Filter    T_start(s)  T_stop(s)  Exposure      Mag  Err
###########################################################
white        156        306         147     19.88 +\- 0.14
white	     5371       5571        197        > 21.26
v	     4345       5981        393        > 19.94
b	     5166       5365        197        > 20.49
u	     314        6572        615        > 20.97
uvw1	     4755       6392        393        > 20.59
uvm2	     4550       6186        393        > 20.46
uvw2	     4140       5777        393        > 20.68
###########################################################

The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525).  The photometry is on the UVOT photometric system
described in Poole et al. (2008, MNRAS, 383,627).

A. de Ugarte Postigo (INAF-OAB), A.J. Castro-Tirado,
M. Jelinek (IAA-CSIC), P. Kubanek (IPL UV, IAA-CSIC),
J. Gorosabel, R. Cunniffe, S. Guziy (IAA-CSIC), P. Yock
(Auckland Univ.), W.H. Allen (Vintage Lane Obs.), I. Bond
(Massey Univ.), G. Christie (Stardome Obs.), report on
behalf of a larger collaboration:

We have observed the field of GRB 091109 (Oates et al. GCN 10138
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 )
using the 0.6 Yock-Allen robotic telescope (BOOTES-3) located in
Bleinheim, New Zealand. Due to bad weather conditions, observations
did not start until 11:03 UT (6.1h after the burst). A combination of  
the
first 30x60s unfiltered exposures does not show any source at the
UVOT postion down to a 3-sigma limiting magnitude of R~20.0,
consistent with the limits given by UVOT (Oates et al. GCN 10143
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 ) and
the fainter detection by Faulkes Telescope South (Guidorzi et al. GCN
10142
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 ).

Further observations are ongoing.

A. P. Beardmore (U. Leicester) and S. R. Oates (UCL-MSSL) report on
behalf of the Swift-XRT team:

We have analysed 7.9 ks of Swift-XRT data for GRB 091109 (Oates et al. 
GCN Circ. 10138
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 ), from 154 s to 18.1 ks after the BAT trigger. The data
span four orbits, comprising 37 s in Windowed Timing (WT) mode with
the remainder in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Beardmore et al. (GCN. Circ 10140).

The light curve can be modelled by a broken power-law with an initial
decay slope of 2.9 +0.5 -0.4, breaking at T+358 s to a shallower decay
of 0.86 +0.07 -0.08.

A spectrum formed from the PC mode data (from 175 s to 18.1 ks after
the trigger) can be fitted with an absorbed power-law, giving a photon
index of 2.10 +/- 0.19. The best-fitting absorption column is (9.9
+2.1 -4.4) x 10^20 cm^-2, in excess of the Galactic value of 3.0 x
10^20 cm^-2 (Kalberla et al. 2005) in the direction of the burst. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.6 x 10^-11 (4.8 x 10^-11) erg cm^-2
count^-1.

If the light curve continues to decay with a power-law decay index of
0.86, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (2.3 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/00375246.

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

L.A. Antonelli, S. Covino, P. D'Avanzo, report on behalf of the REM team:

"We have to correct the position of the object reported in our previous GCN
10139
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 : due to a typo the R.A. position of the putative NIR afterglow of
GRB091109 reported is RA(J2000) 20:37:02.02 instead of RA(J2000) 20:37:02.2.

However, we note that the correct position is still about 2" far away from the
UVOT position (Oates, GCN 10143
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 ). The observed source in the REM H band early
images is very faint and close to the detection limit of our images. So due to
the misplacement with the UVOT position the observed object may be a background
fluctuation not related to GRB091109. A detailed analysis is in progress."




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