GRB 120811C

B. N. Barlow (PSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. Grupe (PSU),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and B.-B. Zhang (PSU)
report on behalf of the Swift Team:

At 15:34:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 120811C (trigger=530689).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 199.709, +62.291 which is 
   RA(J2000)  =  13h 18m 50s
   Dec(J2000) = +62d 17' 29"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single bright peak
with a duration of about 35 sec.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 15:36:00.8 UT, 68.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 199.6833, 62.3027 which is equivalent to:
   RA(J2000)  = +13h 18m 43.99s
   Dec(J2000) = +62d 18' 09.7"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 60 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 2.97e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	13:18:43.81 = 199.68253
  DEC(J2000) = +62:18:02.7  =  62.30076
with a 90%-confidence error radius of about 0.75 arc sec. This position is 7.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.40 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is B. N. Barlow (bnb2 AT 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.)

D. Denisenko, E. Gorbovskoy, V. Lipunov, V. Kornilov, D. Kuvshinov,
A. Belinski, N. Tyurina, N. Shatskiy, P. Balanutsa, D. Zimnukhov,
A. Kuznetsov, V.V. Chazov, A. Sankovich
Lomonosov Moscow State University, Sternberg Astronomical Institute

V. Yurkov, Yu. Sergienko, D. Varda, E. Sinyakov
Blagoveschensk Educational State University, Blagoveschensk

A. Tlatov, A.V. Parhomenko, D. Dormidontov, V. Sennik
Kislovodsk Solar Station of the Pulkovo Observatory

V. Krushinski, I. Zalozhnich, A. Popov, A. Bourdanov, A. Punanova
Ural Federal University

H. Levato, C. Saffe
Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

C. Mallamaci, C. Lopez, F. Podest
Observatorio Astronomico Felix Aguilar (OAFA)
report:

MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru)
located in Blagoveschensk was pointed to GRB 120811C (Barlow et al.,
GCN 13622
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 ) 665 sec after GRB time, at 2012-08-11 15:45:57 UT.
Observations were performed simultaneously in two tubes with mutually
perpendicular polarizations. First two pairs of images were obtained with
130 and 160 sec exposures, followed by the set of 180-sec exposures.
On our images we find the fading optical transient at the coordinates:

  R.A. (J2000) = 13 18 44.01
  Dec. (J2000) = +62 18 02.7

which are consistent with the position of UVOT candidate afterglow
reported in GCN 13622
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 .

Photometry of GRB 120811C afterglow was performed using SDSS
J131828.08+621651.3 (r=14.74) as the reference star. To improve the
signal-to-noise ratio, images were combined by four. The resulting
magnitudes of the afterglow in the Western tube with a better image
quality (FWHM=2.6-3.2") are listed in the Table below.

----------------------------------------------
T_mid UT | T-T0, s | Exptime |  Mag. | Mag.err
---------+---------+---------+-------+--------
15:51:48 | 1016    |  650    |  18.4 |  0.10
16:04:46 | 1794    |  720    |  18.9 |  0.17
16:18:37 | 2625    |  720    |  19.3 |  0.27
16:32:27 | 3455    |  720    |  19.0 |  0.24
16:46:16 | 4284    |  720    | <19.5 |  N/A
17:00:04 | 5112    |  720    | <19.5 |  N/A
----------------------------------------------

The detailed analysis of the complete data set is continuing.

This message can be cited.

Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR),
Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 120811C detected by SWIFT
(trigger 530689) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 3.98h after the GRB trigger.
The elevation of the field decreased from
50 degrees above horizon and weather conditions
were good.

We co-added a series of exposures but we do not find
any optical transcient at the afterglow position
(Barlow et al. GCNC 13622, Denisenko et al. GCNC 13623):

-------------------------------
T-T0 start | T-T0 End |  Mag. |
-----------+----------+-------+
    246 min |  313 min | >19.5 |
-------------------------------

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

This message may be cited.

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

Using 1291 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 120811C, 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 = 199.68285, +62.30068 which is equivalent
to:

RA (J2000): 13h 18m 43.88s
Dec (J2000): +62d 18' 02.4"

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.

A. Galeev (Kazan Federal University), I. Khamitov (TUG),
I. Bikmaev, N. Sakhibullin (Kazan Federal University),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
Z. Eker (TUG), U. Kiziloglu (METU),  E. Gogus (Sabanci Uni.)

report:

We observed the field of the Swift-BAT GRB 120811C (Barlow et al. GCN
13622
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 ) with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe,
TUBITAK National Observatory, Turkey), starting at 11 Aug, 18:52 UT,
i.e. approximately 3.3 hours after the burst, using TFOSC
instrument. We made a serie of 300-600s images in R and V.

The afterglow is detected at the position:

RA=13:18:43.83, DEC=62:18:02.6 (J2000)

with positional error about 0.1 arcsec, which is consistent with that
measured by UVOT and MASTER (Denisenko et al., GCN 13623
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 ).

We measured the afterglow magnitude as m_R=20.00+-0.05 (calibrated
relative to USNO-B1 stars). Observations are continuing.

C. C. Thoene (IAA-CSIC), A. de Ugarte Postigo (IAA-CSIC, DARK), 
J. Gorosabel, R. Sanchez-Ramirez (IAA-CSIC) and 
J. P. U. Fynbo (DARK) G. Gomez Velarde (GTC) report 
on behalf of a larger collaboration:

We observed the afterglow of GRB 120811C (Barlow et al., 
GCN 13622
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 ) with OSIRIS at the 10.4m GTC telescope starting at 
UT 22:07 (6.5 hr after the burst) for a total exposure time of 2400s. 
We used grism 1000B covering the wavelength range between 
3700 and 7800 Angstrom. 

Despite Calima, the continuum is clearly detected and the 
spectrum shows strong Ly alpha and Ly beta absorption as well 
as a number of absorption lines (SII, SiII, OI, CII, CIV, SiIV, AlII, 
AlIII, NiII, ZnII and SiII*) at a common redshift of z=2.671.

P. Kuin, S. R. Oates (MSSL-UCL) and B.N. Barlow (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 120811C
76 s after the BAT trigger (Barlow et al., GCN Circ. 13622
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 ).
A source consistent with the XRT position Evans et al., GCN Circ.
13625
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  is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  13:18:43.82 = 199.68258 (deg.)
    Dec (J2000) = +62:18:02.8  =  62.30077 (deg.)
with an estimated uncertainty of 0.52 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT
photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

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

white               76          226          147         18.59 +/- 0.05
v                  620         1243           78         18.49 +/- 0.19
b                  544          739           39         18.95 +/- 0.19
u                  288          538          246         18.61 +/- 0.09
w1                 670         1464           97        >20.0
m2                 819         1439           78        >20.5
w2                 595         1219           78        >19.7

The absence of a detection in the uv bands is consistent with the reported
redshift from Thoene et al., GCN Circ. 13628
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 .

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).

P.A. Evans (U. Leicester), O.M. Littlejohns (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. Maselli  (INAF-IASFPA), M.C. Stroh
(PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester) and B.N. Barlow report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 120811C (Barlow  et al. GCN
Circ. 13622
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 ), from 56 s to 40.2 ks after the  BAT trigger. The data
comprise 137 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Evans et
al. (GCN. Circ 13625).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=3.12 (+0.13, -0.14). At T+224 s  the decay
flattens to an alpha of 0.44 (+0.12, -0.27) before breaking again at
T+1468 s to a final decay with index alpha=1.06 (+0.19, -0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.74 (+0.14, -0.13). The
best-fitting absorption column is  1.08 (+0.22, -0.20) x 10^21 cm^-2,
in excess of the Galactic value of 2.1 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.00 (+/-0.15) and a
best-fitting absorption column of 8.8 (+3.4, -3.1) x 10^20 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (4.5 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.8 (+3.4, -3.1) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: 3.6 sigma
Photon index:	     2.00 (+/-0.15)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00530689.

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

U.Quadri, L.Strabla and R.Girelli, A.Quadri report:

We imaged the field of GRB 120811C detected 
by SWIFT(trigger 530689) with the robotic 
telescope of (IAU station 565) Bassano Bresciano 
Observatory, Italy.

The observations started 266min. after the 
GRB trigger,with our schmidt telescope 
D=320 mm F/D=3.1.

Weather conditions were good.

We co-added a series of 30 exposures.

We did not found any optical counterpart 
in the error box of the XRTcandidate
(Barlow et al. GCNC 13622).

Start      End       Vlim
266min     326min    19.2

Magnitudes were estimated with the UCAC-3 

The message may be cited.

J. P. U. Fynbo (DARK/NBI), D. Xu (WIS), P. Jakobsson (U. Iceland), D.
Armstrong (U. Warwick), R. Cardenes (NOT) report on behalf of a larger
collaboration:

We observed the optical afterglow of GRB 120811C (Barlow et al., GCN
13622
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 ) using the 2.5m Nordic Optical Telescope (NOT) equipped with
ALFOSC. Spectroscopic observations started at  21:58 UT on 2012-08-11
(i.e., 6.4 hr after the BAT trigger) with exposure time of 3x1800s,
covering the wavelength range of ~3800A to ~8000A. The afterglow was
detected in each of the 1800s frames though the weather was dusty to a
certain degree.

The spectrum exhibits a clear Damped Lyman Alpha (DLA) absorption
feature at about 4460A. Redward of Lyman alpha the spectrum shows
quite a few significant absorption lines, including Si II, O I, C II,
C IV, Si IV, all at a common redshift of z=2.67, in good agreement
with the measurement in Thoene at al. (GCN 13628
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 ).

H. A. Krimm (GSFC/USRA), B. N. Barlow (PSU), S. D. Barthelmy (GSFC),
T. Sakamoto (GSFC/UMBC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), 
N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
G. Sato (ISAS), M. Stamatikos (OSU), 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 120811C (trigger #530689)
(Barlow, et al., GCN Circ. 13622
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 ).  The BAT ground-calculated position is
RA, Dec = 199.690, 62.297 deg, which is 
   RA(J2000)  =  13h 18m 45.5s 
   Dec(J2000) = +62d 17' 50.3" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 89%.
 
The mask-weighted light curve shows a nearly symmetric peak starting at ~T-10 sec,
peaking at ~T+6 sec, and ending at ~T+40 sec.  T90 (15-350 keV) is 26.8 +- 3.7 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-9.7 to T+42.9 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.40 +- 0.30, 
and Epeak of 42.9 +- 5.7 keV (chi squared 59.5 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.0 +- 0.3 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+5.27 sec in the 15-150 keV band is
4.1 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.04 +- 0.06 (chi squared 74.5 for 57 d.o.f.).  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/530689/BA/

K.Ivanov, S.Yazev, N.M.Budnev, O.Gres, O.Chuvalaev, V.A.Poleshchuk
  Irkutsk State University

  E. Gorbovskoy, V. Lipunov, V.Kornilov, D.Kuvshinov, A.Belinski, 
N.Tyurina, N.Shatskiy, P.Balanutsa, D.Zimnukhov, A.Kuznetsov, V.V.Chazov, 
A.Kuznetsov, A.Sankovich
  Sternberg Astronomical Institute, Moscow State University

  V.Yurkov, Yu.Sergienko, D.Varda, E.Sinyakov
  Blagoveschensk Educational State University, Blagoveschensk

  A. Tlatov, A.V. Parhomenko, D. Dormidontov, V.Sennik
  Kislovodsk Solar Station of the Pulkovo Observatory

  V.Krushinski, I.Zalozhnih,  A. Popov
  Ural Federal University, Kourovka

  Hugo Levato and Carlos Saffe
  Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE)

  Claudio Mallamaci, Carlos Lopez and Federico Podest
  Observatorio Astronomico Felix Aguilar (OAFA)


  MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Tunka was pointed to the  GRB120811C (Barlow et al., GCN 13622
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 ) 
40 sec s after notice time and 676 sec after GRB time at 2012-08-11 15:46:08.449 UT. On our 
first (130s exposure) set we have found OT  within SWIFT-BAT error-box in 
two polarizations.

The preliminary robotic photometry (m=0.2B + 0.8R, Usno B magnitudes) is:

datetime	                   coord2000           Band     mag   error

2012-08-11 15:46:08.449	13h 18m 43.90s , +62d 18m 02s.1	P|	17.3	0.2
2012-08-11 15:46:09.684	13h 18m 43.86s , +62d 18m 02s.3	P-	17.2	0.1
2012-08-11 15:49:12.268	13h 18m 43.76s , +62d 18m 02s.3	P|	17.6	0.2
2012-08-11 15:49:12.282	13h 18m 43.93s , +62d 18m 02s.6	P-	17.6	0.2
2012-08-11 15:52:52.452	13h 18m 43.75s , +62d 18m 01s.8	P|	17.8	0.2

So, MASTER-Net have simultaneous optical observations in four 
polarizations (see Denisenko et al., GCN 13623
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 ) of GRB120811C.

The message may be cited.

A. Galeev (Kazan Federal University), I. Khamitov (TUG),
I. Bikmaev, N. Sakhibullin (Kazan Federal University),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
Z. Eker (TUG), U. Kiziloglu (METU),  E. Gogus (Sabanci Uni.)

report:

We continued the observations of the field of the Swift-BAT GRB
120811C (Barlow et al. GCN 13622
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 , Galeev et al., GCN 13626
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 ) with
Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National
Observatory, Turkey). The second epoch observations were started at 
12 Aug, 18:38 UT, i.e. approximately 27.05 hours after the burst. We made
a serie of 300s images in R using TFOSC instrument.

The afterglow was clearly detected in the combined image. Using
USNO-B1 stars as reference, we estimated the afterglow magnitude as
m_R=22.3+-0.2.

Fitting this point together with the data from RTT150 first epoch
observations (Galeev et al., GCN 13626
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 ), gives the power law decay
with index alpha = 1.04 +- 0.05, consistent with late time decay in
X-rays, as it was observed with XRT (Evans et al., GCN 13630
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 ).

When all RTT150 data are compared with the data of MASTER telescopes
(Denisenko et al., GCN 13623
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 , Ivanov et al., 13635), the power law
break at few hours time scale is found, approximately consistent with
the position of second break observed in X-rays with XRT (Evans et
al., GCN 13630
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 ). However, better cross-calibration between RTT and
MASTER photometry should be done for more reliable light curve
modelling.

The light curve and direct images of the field can be found at:

http://hea.iki.rssi.ru/grb/120811c/indexeng.html

T. Laskar, A. Zauderer and E. Berger (Harvard) report:

"We observed the position of GRB 120811C (Barlow et al. GCN 13622
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 ) with the
EVLA at 2012 Aug 11.79 UT (1.14 days after the burst). No significant radio
emission is detected at the enhanced Swift-XRT position (Evans et al. GCN
13625
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 ), the UVOT position (Kuin et al. GCN 13629
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 ) or optical position
(Denisenko et al. GCN 13623
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 ; Galeev et al. GCN 13626
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 ; Ivanov et al. GCN
13635
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 ), to a three-sigma upper limit of 76 uJy at 6.0 GHz."

Peter Jenke (MSFC/NPP) reports on behalf of the Fermi GBM Team:

"At 15:34:55.09 UT on 11 August 2012, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 120811C (trigger 366392098 / 120811649)
which was also detected by the Swift/BAT (Barthelmy et al. 2012, GCN 13622
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 ).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 133 degrees.

The GBM light curve consists of a single pulse 
with a duration (T90) of about 14.3 s (50-300 keV).
The time-averaged spectrum from T0-6.14 s to T0+10.24 s is
best fit by a power law function with an exponential high-energy cutoff.  
The power law index is -0.71 +/- 0.20 and the cutoff energy, 
parameterized as Epeak, is 54 +/- 3 keV.

The event fluence (10-1000 keV) in this time interval is
(2.98 +/- 0.08)E-06 ergs/cm^2. The 1-sec peak photon flux measured
starting from T0+3.072 s in the 10-1000 keV band
is 5.9304 +/- 0.55  ph/s/cm^2.

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

L. Elenin (KIAM), A. Volnova (SAI MSU), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of  GRB 120811C (Barlow et al., GCN  13622
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 ) with 
0.45-m telescope of ISON-NM observatory  starting on  Aug. 12 (UT) 03:25:07. 
We took  several unfiltered images of 30 s exposures.  The optical afterglow 
(Denisenko et al., GCN 13623
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 ) is marginally detected in co-added frames at 
coordinates (J2000) 13:18:43.98 +62:18:03.4 with uncertainty of 0.5 arcsec 
in both coordinates.  A preliminary  photometry of co-added frames is based 
on the USNO-B1.0 (R2)  nearby  stars is following:

T_start,     T0+,           Exposure,  OT,              UL (3 sigma)
(UT)           mid, d         (s)

03:25:07   0.5095      1800           21.5 +/-0.5   21.2

E. Litvinenko (UBAI), A. Volnova (SAI MSU), I. Molotov (KIAM), A. Pozanenko 
(IKI) report on behalf of  larger GRB  follow-up collaboration:

We observed the field of  GRB 120811C (Barlow et al., GCN  13622
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 ) with 
0.4-m telescope of ISON-Kitab observatory  starting on  Aug. 11 (UT) 
15:53:49.  We took  several unfiltered images of 30 s exposures.  The 
optical afterglow  (Denisenko et al., GCN 13623
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 ) is clearly detected in 
single initial frames.  A photometry of some co-added frames is based  on 
the SDSS stars

SDSS id                             RA                 Dec 
R
J131912.45+621444.3 13 19 12,453  +62 14 44,35   16.63
J131815,89+621830,6 13 18 15,896  +62 18 30,67   16.64

is following:

T_start,     T0+,           Exposure,  OT,
(UT)           mid, d         (s)

15:53:49    0.01392    4x30          17,90 +/-0.13
15:56:05    0.01569    5x30          17.95 +/-0.13
15:58:55    0.01841  10x30          18.20 +/-0.10
16:04:35    0.02356  15x30          18.45 +/-0.11
16:13:06    0.03145  25x30          18.40 +/-0.07