GRB 120711B

M. J. Page (UCL-MSSL), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC),
F. E. Marshall (NASA/GSFC), S. R. Oates (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (MSU) report on behalf
of the Swift Team:

At 03:11:02.58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located what may be GRB 120711B (trigger=526270).  Swift slewed immediately
to the position. The BAT on-board calculated location is 
RA, Dec 331.668, +60.020 which is 
   RA(J2000) = 22h 06m 40s
   Dec(J2000) = 60d 01' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve does not show any obvious
variation, which is typical for an image trigger (64 second duration). 

The XRT began observing the field at 03:13:05.6 UT, 123.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 331.69037, 60.02173 which
is equivalent to:
   RA(J2000)  = 22h 06m 45.69s
   Dec(J2000) = +60d 01' 18.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 40 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 does not constrain the column density. 

The initial flux in the 2.5 s image was 8.75e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 260 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 large, but uncertain extinction expected. 

Due to the proximity of the source to the Galactic plane (3.46 degrees),
the fact that this source was detected in the first image following
the SAA, and the relative constancy of the XRT light curve, we
believe that this is more likely to be a previously-unknown
Galactic source rather than a GRB.  However we will need the 
complete downlinked data to determine the nature of the source. 

Burst Advocate for this burst is M. J. Page (mjp 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.)

A. A. Breeveld (MSSL-UCL) and M. J. Page (MSSL-UCL) report on behalf of 
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120711B
260 s after the BAT trigger (Page et al., GCN Circ. 13431
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 ).
No optical afterglow consistent with the XRT position (Page et al., GCN 
Circ. 13431
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 ) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposure and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC           260          410          147         >21.7
white              260          734          186         >21.8
v                  417          784           58         >18.9
b                  516          710           39         >19.8
u                  491          858           58         >19.5
w1                 466          833           58         >18.9
m2                 441          809           58         >19.3
w2                 566         6472          208         >20.2

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 1.13 in the direction of the 
burst (Schlegel et al. 1998).

T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), M. J. Page (UCL-MSSL), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU), J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-141 to T+963 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120711B (trigger #526270)
(Page, et al., GCN Circ. 13431
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 ).  The BAT ground-calculated position is
RA, Dec = 331.710, 59.996 deg, which is 
   RA(J2000)  =  22h 06m 50.5s 
   Dec(J2000) = +59d 59' 46.0" 
with an uncertainty of 3.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 80%.
 
The mask-weighted light curve shows the emission starting ~T-100 sec, 
peaking at ~T+20 sec, and slowly decaying out to T+875 sec.
T90 (15-350 keV) is 60 +- 19 sec (estimated error including systematics).
 
The time-averaged spectrum from T-12.1 to T+51.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.75 +- 0.32.  The fluence in the 15-150 keV band is 5.6 +- 1.2 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+13.11 sec in the 15-150 keV band
is 0.4 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

Contrary to our GCN 13431
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 , we now think that this trigger is very likely GRB,
and not a new Galactic source.
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/526270/BA/

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

We have analysed 4.5 ks of XRT data for GRB 120711B (Page  et al. GCN
Circ. 13431
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 ), from 208 s to 47.2 ks after the  BAT trigger. The data
comprise 106 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. Using 551 s of PC mode data and 2 UVOT
images, we find an enhanced XRT position (using the XRT-UVOT alignment
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =
331.69137, +60.02267 which is equivalent to:

RA (J2000): 22h 06m 45.93s
Dec(J2000): +60d 01' 21.6"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=1.69 (+0.22, -0.17).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.8 (+0.5, -0.4). The
best-fitting absorption column is  2.4 (+0.9, -0.8) x 10^22 cm^-2, in
excess of the Galactic value of 7.2 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.5 (+0.4, -0.3) and
a best-fitting absorption column of 2.9 (+0.7, -0.6) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 9.9 x 10^-11 (1.7 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.9 (+0.7, -0.6) x 10^22 cm^-2
Galactic foreground: 7.2 x 10^21 cm^-2
Excess significance: 5.6 sigma
Photon index:	     1.5 (+0.4, -0.3)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00526270.

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

D. Kuroda (OAO, NAOJ),  H. Hanayama, T. Miyaji, J. Watanabe (IAO, NAOJ),
K. Yanagisawa (OAO, NAOJ), S.Nagayama (NAOJ), M. Yoshida (Hiroshima),
K. Ohta (Kyoto) and N. Kawai(Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 120711B (Page et al., GCNC 13431)
with the optical three color (g', Rc and Ic) CCD camera attached
to the Murikabushi 1m telescope of Ishigakijima Astronomical
Observatory.

The observation started on 2012-07-11 14:35:55 UT (~11.4 h after the burst).
We did not find any new point source within the XRT error
circle (Page et al., GCNC 13431) in all the three bands.

Three sigma upper limits of the OT are listed below.  We used GSC2.3 catalog
for flux calibration.

#T0+[day]  MID-UT    T-EXP[sec]   g'     Rc     Ic
----------------------------------------------------------------------
0.49154    14:58:51   4200.0    >22.1   >21.7  >20.5
----------------------------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]