GRB 110820A

E. Troja (NASA/GSFC/ORAU), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/UMBC), V. D'Elia (ASDC),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), C. B. Markwardt (NASA/GSFC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU),
E. Sonbas (GSFC/USRA/Adiyaman Univ.) and T. N. Ukwatta (MSU) report on
behalf of the Swift Team:

At 17:38:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110820A (trigger=501095).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 343.335, +70.305 which is 
   RA(J2000) = 22h 53m 20s
   Dec(J2000) = +70d 18' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 10 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 17:39:46.8 UT, 79.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 343.1911, 70.2974 which
is equivalent to:
   RA(J2000)  = 22h 52m 45.86s
   Dec(J2000) = +70d 17' 50.5"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 177 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.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.34
x 10^21 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 250 seconds with the U filter
starting  139 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 none of the  XRT error circle. Data from the list of
sources generated on-board are not  available at this time. No
correction has been made for the expected extinction  corresponding to
E(B-V) of 0.55. 

Burst Advocate for this burst is E. Troja (eleonora.troja AT 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.)

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

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

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

V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov
Ural State University, Kourovka

V.Yurkov, Yu.Sergienko, D.Varda, I.Kudelina
Blagoveschensk Educational State University, Blagoveschensk

  MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) 
located in Tunka(Siberia) was pointed to the  GRB110820A 45 sec after 
notice time and 133 sec after GRB time at 2011-08-20 17:40:40.275 UT in 
two polarizations. On  our first (30s exposure) set we haven`t found 
optical transient  within SWIFT error-box.

The 5-sigma upper limit has been about 16.5 mag
  The message may be cited.

V. Rumyantsev,  K. Antoniuk (CrAO), A. Pozanenko (IKI) report on behalf of 
larger GRB  follow-up collaboration:

We observed  the field of the Swift GRB 110820A (Troja  et al., GCN 12288
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 ) 
with AZT-11 telescope of CrAO between  Aug. 20 (UT) 18:23
 - 19:21. Within the XRT error box  (Troja  et al., GCN 12288
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 )  we do not 
detect any source. The photometry is based on the USNO B1.0 star 
1602-0161058    (22:52:45.06 +70:17:17.5) assuming R=18.23:

T0+      Filter,   Exposure, OT,           Upper Limit (3 sigma)
(mid, d)              (s)

0.0520   R        20x180       n/d           21.6

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

Using 1200 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 110820A, 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 = 343.19224, +70.29848 which is equivalent
to:

RA (J2000): 22h 52m 46.14s
Dec (J2000): +70d 17' 54.5"

with an uncertainty of 2.3 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.

D. M. Palmer (LANL), 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), T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU),
E. Troja (NASA/GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+296 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 110820A (trigger #501095)
(Troja, et al., GCN Circ. 12288
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 ).  The BAT ground-calculated position is
RA, Dec = 343.203, 70.298 deg, which is 
   RA(J2000)  =  22h 52m 48.8s 
   Dec(J2000) = +70d 17' 51.2" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.
 
The mask-weighted light curve shows two main peaks.  The first started at ~T-5 sec,
peaking at ~T+2 sec, and ending at ~T+35 sec.  The second starts at ~T+195 sec,
peaking at ~T+230, and ending at ~T+285 sec.  T90 (15-350 keV) is 256 +- 50 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-7.07 to T+264.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.92 +- 0.28.  The fluence in the 15-150 keV band is 8.2 +- 1.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.43 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. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/501095/BA/

$B3'MM(B

$B9uED$G$9!#(B
$B:rHU$N(BGRB110820A$B$N@P3@Eg$N7k2L$G$9!#(B
$B2V;3$5$s$,4QB,$r$7$F$/$l$^$7$?!#(B

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 110820A (Troja et al., GCNC 12288)
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 17:47:41 UT (~9 min after the burst).
We did not find any new point source within the enhanced XRT error
circle (Beardmore et al., GCNC 12291) 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
----------------------------------------------------
0.04719    18:46:24    5280.0   >20.6 >21.3 >19.9
----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]

K.L. Page (U. Leicester) and E. Troja (NASA/GSFC/ORAU) report on behalf
of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 110820A (Troja  et al. GCN
Circ. 12288
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 ), from 82 s to 24.5 ks after the  BAT trigger. The data
comprise 121 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 12291).

The first snapshot of data is dominated by a large flare, also detected
by the BAT (Palmer et al. GCN Circ. 12292
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 ). After around 750 s, the
light curve decay can be fitted with index alpha=0.28 (+0.13, -0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.32 (+0.07, -0.06). The
best-fitting absorption column is  6.1 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 3.3 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.80 (+0.20, -0.26)
and a best-fitting absorption column of 4.7 (+/-1.3) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 5.1 x 10^-11 (7.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.7 (+/-1.3) x 10^21 cm^-2
Galactic foreground: 3.3 x 10^21 cm^-2
Excess significance: 5.9 sigma
Photon index:	     1.80 (+0.20, -0.26)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00501095.

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

Myungshin Im, Won-Kee Park (CEOU/Seoul National Univ), 
Soojong Pak, Giseon Baek, and Youngseok Oh (Kyunghee University)

We observed GRB 100820A (Troja et al. GCN 12288
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 ) with i,z,and 
Y-filters using CQUEAN camera (the Camera for QUasars in the Early uNiverse) 
on the 2.1m telescope at the McDonald observatory. The observation 
started at 2010 August 21, 05:12:48 UT, about 11.5 hrs after the 
BAT trigger.

In a stacked i-band image (3 x 300 sec), we identify a faint object
within the error circle of the enhanced XRT position (Beardmore et al.
GCN 12291
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 ).

The position of the i-band source is

  RA=22:52:49.49
  Dec=70:17:53.6
  with a positional error of ~0.5".

We are carrying our further observations to examine variability 
of the source.

Myungshin Im, Won-Kee Park (CEOU/Seoul National Univ), 
Soojong Pak, Giseon Baek, and Youngseok Oh (Kyunghee University)

The finding chart of the i-band image reported in Im et al.
(GCN 12295
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 ) is available at

http://astro.snu.ac.kr/~mim/grb110820a.html

We also make a correction to the year of the observation
reported in GCN 12295
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 . It should be 2011, not 2010.

Myungshin Im, Won-Kee Park (CEOU/Seoul National Univ), 
Soojong Pak, Giseon Baek, and Youngseok Oh (Kyunghee University)

We revise the position of the afterglow candidate to be

   RA=22:52:46.49
   Dec=70:17:53.6
   with a positional error of ~0.5".

The 2nd set of i-band images were taken 3 hrs after
the 1st set (Im et al. GCN 12295
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 ). Our analysis of the data
shows no significant fading of the object (dm < 0.1  mag)
during that time span.

S. Immler (NASA/CRESST/GSFC) and E. Troja (NASA/GSFC/ORAU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 110820A
139 s after the BAT trigger (Troja et al., GCN Circ. 12288
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 ).
No optical afterglow consistent with the enhanced XRT position
(Beardmore et al., GCN Circ. 12291
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 ) and the position of the
optical afterglow candidate Myungshin et al., GCN Circ. 12297
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 )
is detected in the initial UVOT exposures.

Preliminary 3-sigma upper limits using the UVOT photometric system
(Poole et al. 2008, MNRAS, 383, 627) for the first finding chart (FC)
exposure and subsequent exposures are:

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

u_FC               139          389          246 >20.6
v                  445        24186         1395 >21.1
b                  394        12987          932 >22.0
u                  139        18761         2181 >21.8
w1                 494        18331         2155 >21.8
m2                 469        24536         1716 >20.6
w2                 420        23272         1396 >21.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.55 in the direction of the burst
(Schlegel et al. 1998).

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

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

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

V.Krushinski, I.Zalozhnich, T.Kopytova, A. Popov
Ural State University, Kourovka

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

  MASTER II  robotic telescope (MASTER-Net: http://observ.pereplet.ru) located 
in Tunka(Siberia) was pointed to the  GRB110820A 45 sec after notice time and 
133 sec after GRB time at 2011-08-20 17:40:40.275 UT in two polarizations 
on one in each tube. 
During the analysis of the data of the first hour of observation following 
results have been received:

T-T(GRB)  T-T(GRB)  T-T(GRB)  Exptime    Limit    Filter  Coadd
start[s]  stop[s]   mean [s]    [s]    (5-sigma) 
---------------------------------------------------------------
133        163       148         30      16.4      P_      no
133        163       148         30      16.5      P|      no
133       2797      1465       2040      19.3      P_      14
133       2797      1465       2040      19.6      P|      14
133       2797      1465       4080      19.9     P|+P_    28

Image in filter P_+P| available here
http://observ.pereplet.ru/images/evgeny/GRB110820A.jpg


  The message may be cited.

V.V. Golovnya (Main Astro Obs, Kyiv)
report: 
We have undertaken the review of the sky area in vicinity of 
GRB 110820A (Beardmore GCN Circ.12091
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 ) on astronegatives, 
collected in Ukrainian NAS Main astronomical observatory 
plate archive (1976-1996). All the plates with the possible 
object appearance are digitized using Microtek ScanMaker 
9800XL TMA and Epson Expression 10000XL flatbed scanners and 
have been placed into Golosiiv Plate Archive database DBGPA 
with open access to them.
 
	The list of plates is given in the table:
YYYYMMDD TimeUT	--Plates--	Exp.	LimMag	Star USNOA2 
19830903.220221	GUA040C000207	16.0	15.75	1575-05316204
19841020.183916	GUA040C000521A	16.0	15.75	1575-05316204

Plates: the plate's identifier in GUA040C archive of DWA 
        (D/F=400/2000, M=103"/mm) of the Ukrainian NAS Main
        Astro obs in Kyiv (Marsden's number - 83)[1].
Exp.   - Duration of the maximum exposure (minutes). 
LimMag - Limited V mag, derived in the 15 minutes area around 
       the location given in Beardmore et al. GCN Circ.12091
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 : 
       RA(J2000): 22h 52m 46.14s, Dec(J2000): +70d 17' 54.5"
Star USNOA2 - Comparison star.
  The preview images of 2 areas together with  
the 15x15 min.of arc area from SkyMap can be found in  
http://gua.db.ukr-vo.org/img/grb/110820A/index.html
The images with full resolution are available via e-mail on 
demand.
References: 
1.L.Pakuliak DATABASE of GOLOSIIV PLATE ARCHIVE (DBGPA V2.0),
http://gua.db.ukr-vo.org

Volnova (SAI MSU), E. Litvinenko (UBAI), I. Molotov (Institute of
Applied Mathematics), A. Pozanenko (IKI)

We observed the field of the Swift GRB 110820A (Troja et al., GCN
12288
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 ) with 40-cm telescope ORI-40 of Kitab ISON observatory on Aug.
20 starting on 17:48:45 UT, i.e. 15.5 minutes after the BAT trigger.
On the stacked image we do not detect any source within the enhanced
XRT error box (Beardmore et al., GCN 12291
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 ). The photometry is based
on the USNO B1.0 star USNO-B1.0 1603-0160240, (J2000) RA = 22:52:56.89
Dec = +70:18:37.5, assuming  R 17.19:

 Tstart UT, T0+,        Filter, Exposure, OT, Upper Limit (3 sigma)
                 (mid, d)             (s)

 17:48:45   0.01072   R       5*120        n/d  19.2
 17:48:45   0.02734   R       28*120      n/d  19.6

A. Volnova (SAI MSU), M. Ibrahimov (UBAI), A. Pozanenko (IKI) report
on behalf of larger GRB  follow-up collaboration:

 We observed the field of the Swift GRB 110820A (Troja et al., GCN
12288
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 ) with AZT-22 telescope of Maidanak observatory on Aug. 20
starting on 21:54:54 UT in R band. We took 6 frames with exposure of
300 seconds under good weather condition and seeing (FWHM) of about
0.7". On the stacked image we do not detect the source reported by Im
et al. (GCNs 12295
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 , 12297
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 ). The photometry is based on the USNO B1.0
star USNO-B1.0 1603-0160240, (J2000) RA = 22:52:56.89 Dec =
+70:18:37.5, assuming R =17.19:

 Tstart UT,  T0+,       Filter, Exposure, OT, Upper Limit (3 sigma)
                 (mid, d)            (s)

 21:54:54   0.18924  R        6*300        n/d  22.5