GRB 110731A
GCN Circular 12215
Subject
GRB 110731A: Swift detection of a burst with an optical counterpart
Date
2011-07-31T11:23:28Z (14 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
S. R. Oates (UCL-MSSL), A. P. Beardmore (U Leicester),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
A. Melandri (INAF-OAB), C. J. Mountford (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), C. J. Saxton (UCL-MSSL)
and T. N. Ukwatta (MSU) report on behalf of the Swift Team:
At 11:09:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 110731A (trigger=458448). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 280.521, -28.546 which is
RA(J2000) = 18h 42m 05s
Dec(J2000) = -28d 32' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multiple-peaked
structure with a duration of about 20 sec. The peak count rate
was ~20000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 11:10:36.9 UT, 66.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 280.5042, -28.5363 which is equivalent to:
RA(J2000) = 18h 42m 01.00s
Dec(J2000) = -28d 32' 10.6"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 63 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.
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) = 18:42:01.01 = 280.50419
DEC(J2000) = -28:32:13.7 = -28.53713
with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.80 with a 1-sigma error of about 0.14. 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.)
GCN Circular 12216
Subject
GRB 110731A: FTN+FTS afterglow observations
Date
2011-07-31T12:17:39Z (14 years ago)
From
David Bersier at Liverpool John Moores U <dfb@astro.livjm.ac.uk>
David Bersier (LJMU) report on behalf of a larger collaboration:
The Faulkes Telescopes North (Hawaii) and South (Australia) both started
automatically (110 and 182 seconds after trigger) to observe GRB
110731A, in response to the Swift trigger 458448. The software detected
a uncatalogued decaying source that coincides with the position of the
UVOT candidate afterglow (GCN 12215).
We measure a magnitude mR=16.4 at 28 minutes after the trigger time.
Assuming a power law decay, the decay index is about -1.
Observations have been obtained with the BVR filters and are continuing
on both telescopes.
GCN Circular 12217
Subject
GRB 110731A: Swift-BAT refined analysis
Date
2011-07-31T13:58:26Z (14 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC),
S. R. Oates (UCL-MSSL), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
M. Stamatikos (OSU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
Using the data set from T-240 to T+402 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 110731A (trigger #458448)
(Oates, et al., GCN Circ. 12215). The BAT ground-calculated position is
RA, Dec = 280.513, -28.536 deg, which is
RA(J2000) = 18h 42m 03.1s
Dec(J2000) = -28d 32' 10.0"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 98%.
The mask-weighted light curve shows many overlapping peaks starting at ~T-1.5 sec,
peaking at +T_zero, and ending at ~T+8 sec with a long exponential decay
lasting out to ~T+80 sec. T90 (15-350 keV) is 38.8 +- 13.0 sec
(estimated error including systematics).
The time-averaged spectrum from T-1.3 to T+80.3 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.15 +- 0.05. The fluence in the 15-150 keV band is 6.0 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.26 sec in the 15-150 keV band
is 11.0 +- 0.3 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/458448/BA/
GCN Circular 12218
Subject
Fermi-LAT Detection of GRB110731A
Date
2011-07-31T18:13:26Z (14 years ago)
From
Julie McEnery at NASA/GSFC <julie.e.mcenery@nasa.gov>
Johan Bregeon, Julie McEnery and Masanori Ohno report on
behalf of the Fermi Large Area Telescope (LAT) collaboration.
Based on an on-ground analysis, the Large Area Telescope (LAT),
on-board the Fermi Gamma-ray Space Telescope, detected high energy
emission above 100 MeV, with greater than 10 sigma significance, from
the Swift detected burst GRB 110731A (Oates et al, GCN 12215).
The preliminary LAT location of the ground automated analysis
is (Ra,Dec) = (280.39,-28.53)+/-0.20 d (68% cont.) which is consistent
with the Swift localization and within 0.1d from the optical
counterpart position.
Further analysis is ongoing.
The Fermi LAT point of contact for this burst is Johan Bregeon
(johan.bregeon@pi.infn.it).
The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of
an international collaboration between NASA and DOE in the U.S. and
many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 12219
Subject
GRB 110731A: Enhanced Swift-XRT position
Date
2011-07-31T18:18:07Z (14 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1566 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 110731A, 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 = 280.50417, -28.53748 which is equivalent
to:
RA (J2000): 18h 42m 1.00s
Dec (J2000): -28d 32' 14.9"
with an uncertainty of 1.4 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.
GCN Circular 12220
Subject
GRB 110731A: NOT photometry
Date
2011-07-31T23:11:39Z (14 years ago)
From
Giorgos Leloudas at Dark Cosmology Centre <giorgos@dark-cosmology.dk>
D. Malesani, G. Leloudas (DARK/NBI), Dong Xu (WIS), A. de Ugarte Postigo, J. Hjorth (DARK/NBI), P. Jakobsson (U. Iceland), and M. B. Nielsen (NOT), report on behalf of a larger collaboration.
We used the Nordic Optical Telescope (La Palma, Spain) equipped with ALFOSC to observe the field of GRB 110731A (Oates et al., GCN 12215). Observations started at 21:22 UT, i.e. 10.22 hr after the trigger. We obtained 3x300 s in R under bad (1.7") seeing conditions.
The afterglow has faded considerably with respect to the report by Bersier (GCN 12216). Photometry is made difficult by the crowding of the field, and we estimate a tentative magnitude for the transient R = 22.2 +- 0.3 mag.
GCN Circular 12221
Subject
GRB 110731A: Fermi GBM observation
Date
2011-08-01T06:29:38Z (14 years ago)
From
David Gruber at MPE <dgruber@mpe.mpg.de>
David Gruber (MPE) reports on behalf of the Fermi GBM Team:
"At 11:09:29.94 UT on 31 July 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110731A (trigger 333803371 / 110731465)
which which was also detected by Fermi LAT (Bregeon et al. 2011, GCN 12218)
and Swift (Oates et al. 2011, GCN 12215).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 6 degrees.
Moreover, this burst was bright enough to result in a Fermi spacecraft
autonomous rapid repoint (ARR) maneuver.
The GBM light curve consists of one pulse
with a duration (T90) of about 7.3 +/- 0.3 s (50-300 keV).
The time-averaged spectrum from T0 s to T0+7.3 s is
best fit by a power law function with an exponential
high-energy cutoff. The power law index is -0.82 +/- 0.03 and
the cutoff energy, parameterized as Epeak, is 317 +/- 10 keV.
The event fluence (10-1000 keV) in this time interval is
(2.218 +/- 0.006)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.128 s in the 10-1000 keV band
is 20.9 +/- 0.5 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 304 +/- 13 keV, alpha = -0.80 +/- 0.03 and beta = -2.98 +/- 0.30.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 12222
Subject
GRB110731A: Swift/UVOT Observations
Date
2011-08-01T12:17:25Z (14 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL-UCL) reports on behalf of the Swift-UVOT team
The Swift/UVOT began settled observations of the field of GRB 110731A 75s
after the trigger (Oates et al., GCN Circ. 12215). We detect a fading
source in the white, v, b and u filters at a refined position of
RA(J2000), DEC(J2000)= 280.50413 deg, -28.537167 deg. This is equivalent to:
RA (J2000) 18:42:00.99
Dec (J2000) -28:32:13.8
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
This is consistent with the UVOT position reported in Oates et al.
(GCN Circ. 12215) and with the enhanced position of the X-ray afterglow
(Beardmore et al., GCN Circ. 12219). The non-detection in the uv filters is
consistent with a redshift of between 2 and 3.
Preliminary magnitudes using the UVOT photometric system (Poole et al. 2008,
MNRAS, 383, 627) for the finding chart (FC) and summed exposures at the
location of the optical afterglow are:
Filter T_start(s) T_stop(s) Exp(s) Mag
#####################################################
wh (FC) 75 225 147 15.85+/-0.02
wh 567 587 19 17.64+/-0.11
v 790 810 19 16.90+/-0.23
b 542 562 19 17.87+/-0.23
u (FC) 287 537 246 17.71+/-0.08
u 1118 1138 19 18.37+/-0.44
uvw1 666 1286 78 >18.88
uvm2 642 1261 78 >18.77
uvw2 592 1385 97 >19.24
#####################################################
We note that photometry is difficult due to the field being crowded and the presence of a faint
contaminating source in the source region. The values quoted above are not
corrected for the non-negliable Galactic extinction due to the reddening
of E(B-V) = 0.18 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 12223
Subject
Konus-Wind observation of GRB 110731A
Date
2011-08-01T12:53:47Z (14 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the
Konus-Wind team, report:
The long GRB 110731A (Swift-BAT trigger #458448: Oates, et al., GCN
12215; Krimm et al., GCN 12217; also detected by Fermi-LAT: McEnery, GCN
12218, and Fermi-GBM: Gruber, GCN 12221) triggered Konus-Wind at
T0=40174.604 s UT (11:09:34.604).
The burst light curve shows a multipeaked structure with a duration of
~7 s. There is a low-level emission seen in the G2 band (~80-360 keV) up
to ~T0+40 s.
As observed by Konus-Wind the burst
had a fluence of 1.63(-0.10,+0.11)x10^-5 erg/cm2,
and a 64-ms peak flux measured from T0+4.304 s
of (6.0 +/- 1.3)x10^-6 erg/cm2/s
(both in the 20 keV - 6 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+8.448 s) can be fitted (in the 20 keV - 6 MeV
range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep), with
alpha = -0.74(-0.15, +0.16), and
Ep = 288(-25, +30) keV (chi2 = 98.2/76 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.92 (chi2 = 98.1/75 dof).
All the quoted errors are at the 90% confidence level.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB110731_T40174/
GCN Circular 12224
Subject
GRB 110731A: Swift-XRT refined Analysis
Date
2011-08-01T12:54:32Z (14 years ago)
From
Owen Littlejohns at U of Leicester <oml2@le.ac.uk>
O. M. Littlejohns, P. A. Evans, A. P. Beardmore (U. Leicester) and S.
R. Oates (UCL-MSSL) report on behalf of the Swift-XRT team:
We have analysed 8.1 ks of XRT data for GRB 110731A (Oates et al. GCN
Circ. 12215), from 56 s to 36.0 ks after the BAT trigger. The data
comprise 607 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 Beardmore
et al. (GCN. Circ 12219).
The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.04 (+0.05, -0.10). At T+502 s the decay
steepens to an alpha of 1.183 (+0.027, -0.024) before breaking again at
T+29.0 ks to a final decay with index alpha=4.2 (+5.8, -2.0). We note
that the uncertainty in this final decay is large due to the small
number of data points after the final break.
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.08 (+/-0.05). The
best-fitting absorption column is 2.05 (+0.14, -0.13) x 10^21 cm^-2,
in excess of the Galactic value of 1.0 x 10^21 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.92 (+/-0.12) and a
best-fitting absorption column of 1.7 (+0.4, -0.3) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 4.0 x 10^-11 (5.5 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.7 (+0.4, -0.3) x 10^21 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: 8.4 sigma
Photon index: 1.92 (+/-0.12)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00458448.
This circular is an official product of the Swift-XRT team.
GCN Circular 12225
Subject
GRB 110731A Gemini-N redshift
Date
2011-08-01T13:23:44Z (14 years ago)
From
Nial Tanvir at U.Leicester <nrt3@star.le.ac.uk>
N. R. Tanvir, K. Wiersema (U. Leicester), A. J. Levan (U. Warwick), S. B. Cenko (U. Berkeley)
and T. Geballe (Gemini) report on behalf of a larger collaboration:
We observed the location of GRB 110731A (Oates et al. GCN12215) with
the GMOS-N instrument on Gemini-North (Mauna Kea), beginning at 1 Aug 2011
09:07 UT.�� Spectroscopic observations totalling 3600s were obtained in good
conditions using the B600 grating (spanning approximately 3800 A to 6650 A).��
We identify a broad Ly-alpha absorption feature and several absorption lines of
O, C, Si and Al at a common redshift of z=2.83.�� This includes fine structure lines
of O, C and Si, as seen in other GRB sight-lines, confirming that this is the
redshift of the burst.
Provisional calibration of the acquisition image gives a magnitude of R=22.0 for
the afterglow (uncorrected for foreground extinction of A_R ~ 0.5),�� suggesting
a fairly shallow rate of decay since the NOT epoch (Malesani et al. GCN12220).
GCN Circular 12226
Subject
GRB110731A: MITSuME Ishigakijima Optical Upper Limits
Date
2011-08-01T14:10:02Z (14 years ago)
From
Daisuke Kuroda at OAO/NAOJ <dikuroda@oao.nao.ac.jp>
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 110731A (Oates et al., GCNC 12215)
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 13:02:23 UT (~1.9 h after the burst).
We did not find any new point source within the enhanced XRT error
circle (Beardmore et al., GCNC 12219) in all the three bands. We
could not detect the previously reported afterglow
(Bersier, GCNC 12216; Malesani et al., GCNC 12220).
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
----------------------------------------------------
0.12025 14:02:40 6180.0 >21.8 >20.6 >20.1
----------------------------------------------------
T0+ : Elapsed time after the burst [day]
T-EXP: Total Exposure time [sec]
GCN Circular 12227
Subject
GRB 110731A / EVLA upper limits
Date
2011-08-01T19:02:55Z (14 years ago)
From
Ashley Zauderer at CfA <bevinashley@gmail.com>
A. Zauderer, E. Berger (Harvard), and D.A. Frail (NRAO) report on
behalf of a larger collaboration:
"We observed the Swift burst GRB 110731A (GCN 12215) with the EVLA
beginning on 2011 Aug 1.15 UT (0.68 days after the burst).
Observations were performed at 5.75 and 22 GHz for about 30 min
at each frequency. No radio source is detected in coincidence
with the optical afterglow (GCN 12215), to a 3-sigma limit of
~50 microJy at 5.75 GHz. Additional observations are planned."
GCN Circular 12242
Subject
GRB110731A: MOA optical observations of the steeply fading afterglow
Date
2011-08-03T11:49:40Z (14 years ago)
From
Akihiko Fukui at Nagoya U/MOA <afukui@stelab.nagoya-u.ac.jp>
P. J. Tristram (MJUO), A. Fukui (Nagoya U.), K. Ohnishi (Nagano NCT) and T. Sako (Nagoya U.)
report on behalf of the MOA collaboration.
We began prompt observations of the afterglow of GRB110731A (Oates et al., GCN 12215)
at July 31 11:12:47 UT responding to the Swift trigger 458448 (3.3 min after the trigger)
using the 61 cm B&C telescope at the Mt John University Observatory in New Zealand.
We obtained a series of I and V band images with 60 sec exposure times followed by some
120 sec exposures until 12:56 UT (105 min after the trigger).
The total number of I and V images are 39 and 35, respectively.
Although the first image had a poor psf, the following images had well-shaped psf's and
we confirmed the steeply fading afterglow, which is consistent with the previous reports
(e.g. Bersier et al. GCN 12216), on these images in both the I and V bands.
The afterglow is located within the error circle reported by Oates et al. GCN 12222.
The magnitude of the afterglow on the second and on the last images in the I band obtained
by psf-fitting photometry with the DoPHOT package
(Schechter et al. 1993) and calibrated to the USNO-B1.0 N magnitude (similar to I magnitude)
follow.
------------------------------------------
Filter mid_JD-2450000 exptime[sec] dT[min] Nmag error
I 5773.96831 60 4.86 14.75 0.20
I 5774.03807 120 105.31 20.2 2.7
------------------------------------------
Here dT denotes the difference between the mid_JD (mid time of exposure) and the trigger
time. The large error in the magnitude of the last image resulted from the calibration relying on extrapolation.
GCN Circular 12244
Subject
GRB 110731A : Suzaku WAM observation of the prompt emission
Date
2011-08-04T02:12:35Z (14 years ago)
From
Yoshitaka Hanabata at Hiroshima U <hanabata@hep01.hepl.hiroshima-u.ac.jp>
Y. Hanabata, T. Uehara, T. Takahashi, M. Mizuno, M. Ohno, Y. Fukazawa
(Hiroshima U.), T. Yasuda, Y. Terada, M. Tashiro, W. Iwakiri,
K. Takahara (Saitama U.), S. Sugita (Nagoya U.), K. Yamaoka (Aoyama
Gakuin U.), M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa (Waseda U.),
N. Ohmori, M. Akiyama, M. Yamauchi (Univ. of Miyazaki), Y. Urata,
P. Tsai, C-J. Chuang (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo),
on behalf of the Suzaku WAM team, report:
The bright long GRB110731A (Swift/BAT trigger #458448: Oates et al.
GCN 12215, also detected by Fermi-LAT: Bregeon et al. GCN 12218)
triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers
an energy range of 50 keV - 5 MeV at 11:09:30.211 UT (=T0).
The observed light curve shows multiple peaks starting at T0-1.5 s, ending
at T0+7.5 s, with a duration (T90) of about 6.56 seconds. The fluence in
100 - 1000 keV was 1.31 (-0.12, +0.08) x 10^-5 erg/cm^2. The 1-s peak
flux measured from T0+3.5 s was 5.20 (-0.70, +0.57) photons/cm^2/s in the
same range.
Preliminary result shows that the time-averaged spectrum from T0-1.5 s to
T0+7.5 s is well fitted by a power-law with exponential cutoff model:
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha 0.93 (-0.66, +0.57), and
Epeak 339 (-51, +40) keV (chi^2/d.o.f. = 11.2/12).
The light curves for this burst will be available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular 12333
Subject
GRB 110731A: SAO RAS and Terskol observations
Date
2011-09-09T08:30:16Z (14 years ago)
From
Vladimir Sokolov at SAO RAS <sokolov@sao.ru>
A. S. Moskvitin, V. V. Sokolov, O. I. Spiridonova (SAO RAS, Russia),
M. V. Andreev, A. V. Sergeev, N. A. Parakhin (Terskol Branch of Institute of
Astronomy, Russia)
We observed the field of GRB 110731A (Oates et al., GCN 12215) on July, 31
with 0.6-m Zeiss-600 (Terskol Branch of Institute of Astronomy, Russia)
equipped with the PixelVision Vienna CCD (1024 x 1024, bin 2 x 2)
+ R filter, and 1-m Zeiss-1000 (SAO RAS, Russia) equipped with the
E2V 42-40 CCD (2048 x 2048, bin 2 x 2) + B and Rc filters. In both cases
the observations carried out at a high airmass and with the seeing ~4".
At all stacked images we did not detect any source within the Swift/UVOT
error circle (Oates., GCN 12222). Close to the error circle are visible two
objects which are also present in the USNO-B.1 catalogue:
S1: USNO-B.1 0614-0802286 (R.A.=18:42:00.72, Dec.=-28:32:14.9, E.=2000.0) &
S2: USNO-B.1 0614-0802328 (R.A.=18:42:01.24, Dec.=-28:32:11.6, E.=2000.0).
Our astrometric calibration and photometry of S1 object showed
that it can contain flux from OT but due to large seeing we can not
distinguish bright S1 and faint OT.
All three co-added images are shown at
ftp://ftp.sao.ru/pub/grb/GRB110731A/GRB110731A.jpg
Upper limits are shown at the following table.
_________________________________________________________
mid. time, UT filter exp., sec 3-sigma lim. telescope
_________________________________________________________
19:15 R 53 x 200 19.9 Zeiss-600
19:24 Rc 31 x 60 21.7 Zeiss-1000
19:38 B 22 x 60 20.8 Zeiss-1000
_________________________________________________________
We use USNO-B.1 star 0614-0802353 (R.A.=18:42:01.83, Dec.-28:32:23.9,
E.=2000.0, B2 = 15.77, R2 = 14.29) as a standard, and did not apply Galaxy
extinction correction.
This message can be cited.