GRB 071020
GCN Circular 6949
Subject
GRB 071020: Swift detection of a bright burst
Date
2007-10-20T07:18:57Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
S. T. Holland (CRESST/USRA/GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
T. Sakamoto (NASA/UMBC), R. L. C. Starling (U Leicester) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 07:02:26 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 071020 (trigger=294835). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 119.664, +32.861 which is
RA(J2000) = 07h 58m 39s
Dec(J2000) = +32d 51' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a double peak
structure with a duration of about 5 sec. The peak count rate
was ~22000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 07:03:28 UT, 61 seconds after the
BAT trigger. In 268 s of promptly downlinked data XRT found a bright, fading,
uncatalogued X-ray source located at RA, Dec 119.6656, 32.8611 which is
RA(J2000) = 07 58 39.74
Dec(J2000) = +32 51 40.0
with an uncertainty of 4.3 arcsec (radius, 90% containment).
This location is 5 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 1.8e-09 erg/cm2/s (0.2-10 keV).
There will be no UVOT data products for this burst, because it is still in
engineering mode after the recent recovery to the new 3-gyro mode.
Burst Advocate for this burst is S. T. Holland (sholland AT milkyway.gsfc.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.)
GCN Circular 6950
Subject
GRB071020 - SDSS Pre-burst Observations
Date
2007-10-20T07:30:59Z (18 years ago)
From
Richard J. Cool at U.of AZ/Steward Obs <rcool@as.arizona.edu>
Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona),
David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel
(LBNL), J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald
P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report:
The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB071020 prior to the burst. As these data should be useful
as a pre-burst comparison and for calibrating photometry,
we are supplying the images and photometry measurements for
this GRB field to the community.
Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB071020
We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=119.664 (07:58:39.4),
dec=32.8610 (32:51:39.6); Swift-BAT TRIGGER 294835), as well
as 3 gri color-composite JPGs (with different stretches). The
units in the FITS images are nanomaggies per pixel. A pixel
is 0.396 arcsec on a side. A nanomaggie is a flux-density unit
equal to 10^-9 of a magnitude 0 source or, to the extent that
SDSS is an AB system, 3.631e-6 Jy. The FITS images have WCS
astrometric information.
In the file GRB071020_sdss.calstar.dat, we report photometry
and astrometry of 741 bright stars (r<20.5) within 15' of the
burst location. The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected
in the u-band; use the errors and object flags to monitor
data quality.
In the files GRB071020_sdss.objects_flux.dat and
GRB071020_sdss.objects_magnitudes.dat, we report photometry
of 975 objects detected within 6' of the GRB position.
We have removed saturated objects and objects with model
magnitudes fainter than 23.0 in the r-band. The fluxes listed
in GRB071020_sdss.objects_flux.dat are in nanomaggies while
the magnitudes listed in GRB071020_sdss.objects_magnitudes.dat
are asinh magnitudes.
All quantities reported are standard SDSS photometry, meaning
that they are very close to AB zeropoints and magnitudes are
quoted in asinh magnitudes. Photometric zeropoints are known
to about 2% rms. None of the photometry is corrected for
dust extinction. The Schlegel, Finkbeiner, and Davis (1998)
predictions for this region are A_U=0.335 mag, A_g=0.246 mag,
A_r = 0.179 mag, A_i=0.135 mag, and A_z=0.096 mag.
The file GRB071020_sdss.spectro.dat contains a list of the
3 objects with SDSS spectroscopy within 6 arcminutes of the
GRB position. In addition to the redshift and 1-sigma error
for each object, this file also lists the object spectroscopic
classification.
SDSS astrometry is generally better than 0.1 arcsecond per
coordinate. Users requiring high precision astrometry should
take note that the SDSS astrometric system can differ from
other systems such as those used in other notices; we have
not checked the offsets in this region.
More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et
al. 2006, PASP 118, 733). See the SDSS DR4 documentation for
more details: http://www.sdss.org/dr5.
These data have been reduced using a slightly different
pipeline than that used for SDSS public data releases.
We cannot guarantee that the values here will exactly match
those in the data release in which these data are included.
In particular, we expect the photometric calibrations to differ
by of order 0.01 mag.
This note may be cited, but please also cite the SDSS data
release paper, Adelman-McCarthy et al. (2006, ApJS, 172, 634),
when using the data or referring to the technical documentation.
GCN Circular 6951
Subject
GRB 071020: ROTSE-III Analysis of Optical Counterpart
Date
2007-10-20T08:07:20Z (18 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan (U Mich), E.S. Rykoff (UCSB), T.A. McKay (U Mich), B. E.
Schaefer (Louisiana State), R. Quimby (Caltech), H. Swan (U Mich),
report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
071020 (Swift trigger 294835; Holland, et al., GCN6949) and detected the
optical counterpart (Schaefer, et al., GCN 6948). During our first 80
seconds observation (starting 25.6 sec after the burst), the OT faded
with a decay index of 1.52 +/- 0.03.
We notice that the burst location is 9.7h^-1 kpc from the central bulge
of SDSS J075843.38+325141.7, a galaxy with an old stellar population
located at z=0.0166. DR6 SDSS data suggest this galaxy as M_r ~ -19.4,
and a central velocity dispersion of 135 km/s.
GCN Circular 6952
Subject
GRB 071020: VLT spectroscopy
Date
2007-10-20T13:40:12Z (18 years ago)
From
Pall Jakobsson at U Hertfordshire <P.Jakobsson@herts.ac.uk>
Pall Jakobsson (U. Hertfordshire), Paul M. Vreeswijk,
Jens Hjorth, Daniele Malesani, Johan P.U. Fynbo and
Christina C. Thoene (DARK, NBI) report:
Using FORS2 on the Very Large Telescope, we have obtained
a 10 min spectrum (grism 300V) of the optical afterglow
(OA) of GRB 071020 (Holland et al., GCN 6949). The acquisition
image shows the proposed OA (Schaefer et al., GCN 6948) to
have R ~ 20.4 on Oct 20.377 (2.0 hours post burst).
The spectrum displays Fe II (2586,2600) and the Mg II
doublet (2796,2803) in absorption corresponding to a redshift
of z = 2.145 (based on a preliminary wavelength calibration).
Hence, the GRB is unrelated to the nearby z = 0.0166 galaxy
reported by Yuan et al. (GCN 6951).
We note that this is a lower limit to the GRB redshift.
There is some indication of a flux drop in the OA spectrum
around 4300 A, implying that the GRB redshift could be
z ~ 2.5 if due to the Ly-alpha break.
We thank the Paranal staff for excellent support,
especially Emanuela Pompei.
GCN Circular 6954
Subject
GRB 071020, Swift-BAT refined analysis
Date
2007-10-20T16:46:43Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Tueller (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), S. T. Holland (CRESST/USRA/GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), J. Norris (U. Denver),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+625 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 071020 (trigger #294835)
(Holland, et al., GCN Circ. 6949). The BAT ground-calculated position is
RA, Dec = 119.666, 32.857 deg, which is
RA(J2000) = 07h 58m 39.9s
Dec(J2000) = 32d 51' 25"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 90%.
The mask-weighted lightcurve shows at least 8 overlapping pulses in the initial
burst. They all have approximately the same peak flux values. This emission
starts at ~T-3 sec, peaks at ~T-1.5 sec, and ends at ~T+0.9 sec.
T90 (15-350 keV) is 4.2 +- 0.2 sec (estimated error including systematics).
The spectral lag for this burst is:
59 +7-9 msec for the 150-300 to 25-50 keV bands, and
10 +8-7 msec for the 50-100 to 15-25 keV bands.
The time-averaged spectrum from T-3.0 to T+7.4 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.11 +- 0.05. The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.36 sec in the 15-150 keV band
is 8.4 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
Folding in the borderline results of the T90, the hardness ratio,
the spectral lag, and very marginal detection of extended emission in the lightcurve;
we think this is a Long burst, but we can not rule out the possibility
of a SHB classification.
GCN Circular 6955
Subject
GRB 071020: Swift-XRT refined analysis
Date
2007-10-20T19:03:38Z (18 years ago)
From
Andy Beardmore at U Leicester <apb@star.le.ac.uk>
A.P. Beardmore, K.L. Page, P.A. Evans (U. Leicester) and S.T. Holland
(CRESST/USRA/GSFC) report on behalf of the Swift-XRT team:
The Swift-XRT began observing the BAT GRB 071020 (trigger #294835) at
07:03:28 UT, 61 seconds after the BAT trigger. In a 1.23ks
exposure Photon Counting mode image obtained during the first orbit
we find a refined XRT position of RA, Dec (J2000) = 119.66521, 32.86079
which is
RA(J2000) = 07:58:39.65
Dec(J2000) = +32:51:38.8
with an estimated uncertainty of 4.0 arcsec (radius, 90 percent
containment). This is 13.9 arcsec from the refined BAT position
(Tueller et al., GCN 6954), 4.1 arcsec from the position
of the ROTSE-IIIb afterglow (Schaefer et al., GCN 6948), and
2.3 arcsec from the PAIRITEL position (Bloom et al., GCN 6953).
Due to a high CCD operating temperature caused by the unfavourable sky
position of the burst, along with bright Earth activated hot-pixels,
the XRT remained in Windowed Timing mode for orbits 2 to 5 at which
point the initial Swift observations were halted for today. However,
using the XRT data available at these times, the 0.3-10.0keV X-ray
light curve from T+68s to T+17.6ks shows a powerlaw decline with a
decay index of 1.11+/0.02.
The Windowed Timing mode spectrum from the first orbit (T+68s to
T+315s) is well fit by an absorbed powerlaw with a photon index of
1.86+/-0.07 and a redshifted column density of (4.3+/-1.7)e21 cm^-2
(at z=2.145, Jakobsson et al., GCN 6952), in addition to the 5.1e20
cm^-2 galactic column density in this direction. The observed 0.3-10.0
keV flux during this time is (6.1+/-0.2)e-10 erg cm^-2 s^-1.
Assuming the X-ray light curve decays at the same rate we predict an
XRT count rate of 0.014 count s^-1 at T+24 hours, which corresponds to an
observed 0.3-10keV flux of 6.0e-13 erg cm^-2 s^-1.
This circular is an official product of the Swift-XRT team.
GCN Circular 6960
Subject
Konus-Wind observation of GRB 071020
Date
2007-10-21T13:31:43Z (18 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
and T. Cline on behalf of the Konus-Wind team report:
The long GRB 071020 (Swift-BAT trigger #294835:
Holland et al., GCN 6949, Tueller et al., GCN 6954) triggered
Konus-Wind at T0=25346.637 s UT (07:02:26.637).
The burst light curve shows a multipeaked structure
with a duration of ~3.5 s.
As observed by Konus-Wind the burst
had a fluence of 7.71(-4.76, +0.39)x10^-6 erg/cm2,
and a 64-ms peak flux measured from T0+2.416 s
of 6.04(-3.88, +1.12)x10^-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+8.448 s) is well fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep)
with alpha = 0.65(-0.32, +0.27)
and Ep = 322(-53, +80) keV (chi2 = 64.4/61 dof).
Fitting by GRBM (Band) model yields only an upper limit
on the high energy photon index: beta < -1.97.
All the quoted errors are at the 90% confidence level.
Assuming z = 2.145 (Jakobsson et al., GCN 6952)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.3, Omega_\Lambda = 0.7,
the isotropic bolometric energy release is E_iso ~8x10^52 erg, and
the maximum bolometric luminosity is (L_iso)_max ~2x10^53 erg/s.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB071020_T25346/
GCN Circular 6970
Subject
GRB 071020: Fading slowly?
Date
2007-10-22T01:04:37Z (18 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im, I. Lee (Seoul National University), and Y. Urata
(Saitama University) on behalf of the EAFON team:
Using the Mt. Lemmon (Arizona, US) 1.0m telescope
operated by the Korea Astronomy Space Science Institute,
we observed GRB071020 (GCN 6949, Holland et al.),
beginning at 09:01:45 UT on Oct 21. (1.0825 days after the burst).
We confirm the afterglow (GCN6948 Schaefer, McKay, & Yuan; GCN6956,
Xin et al.; GCN6953, Bloom et al.).
Compared with the photometry in the report by Xin et al. (GCN6956),
our data suggest that the afterglow is not fading signficiantly over
the 12 hrs span and may even be brightenning by a small amount.
Since the target is still bright enough for small telescopes,
we encourage the further observations of this object.
Photometry of the object is given below.
t_start (UT) Filter exp (sec) R-mag err
-----------------------------------------------------
Oct. 21,
09:01:45 R 15x300 20.93 0.09
This message may be cited.
We acknowldege the help for a series of LOAO GRB
observations by the LOAO operators, J.H. Yoon and I.K. Baek.
GCN Circular 6978
Subject
Radio detection of GRB 071020 with the VLA
Date
2007-10-22T18:59:06Z (18 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of the
Caltech-NRAO-Carnegie GRB Collaboration:
"We observed the field centered on the XRT position of the Swift burst
GRB 071020 (GCN 6949) using the VLA at a frequency of 8.46 GHz.
The observations were taken at a mean time of 11.21 UT on 22nd Oct 07.
We detect the radio afterglow of GRB 071020 at the following position:
RA(J2000) 07 58 39.78
Dec(J2000) +32 51 39.56
The flux density of the GRB is 186+/-26 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 6979
Subject
GRB 071020: SARA observations
Date
2007-10-22T20:23:05Z (18 years ago)
From
Adria C. Updike at Clemson U <aupdike@clemson.edu>
Adria C. Updike, Dieter H. Hartmann (Clemson University) and Todd
Hillwig (Valparaiso University) report on behalf of the Clemson GRB
Follow-Up Team:
We observed the field of GRB 071020 (GCN 6949, Holland et al.) beginning
1 hour after the trigger with the SARA 0.9m telescope on Kitt Peak. In
48 minutes of stacked exposures, we detect the afterglow (GCN 6948,
Schaefer et al.) in the R band at 19.7 +/- 0.2, calibrated relative to
10 field stars in the USNO B1.0 catalog. Observations ended at 2 hours
and 11 minutes after the burst.
This message may be cited.
Information on the SARA observatory may be found at
http://astro.fit.edu/sara/sara.html .
GCN Circular 6981
Subject
Optical observations of GRB 071020
Date
2007-10-23T11:25:46Z (18 years ago)
From
AAVSO GRB Network at AAVSO <matthewt@aavso.org>
Veli-Pekka Hentunen (Taurus Hill Observatory, Varkaus, Finland) reports to
the AAVSO International High Energy Network the following optical
observations of GRB071020 (GCN #6949, Holland et al.):
Markku Nissinen, Henri Taino and Veli-Pekka Hentunen report the detection
of the optical afterglow of GRB 071020 (Holland et al., GCN 6949; Schaefer
et al., GCN 6948; Yuan et al., GCN 6951; Xin et al., GCN 6956). The
afterglow was observed unfiltered approximately 17 hours post-burst, using
a 0.3-meter Meade LX200 at Taurus Hill Observatory. The source was
detected with marginal signal to noise at an unfiltered magnitude of 20.9
+/- 0.3, with an observational mid-point time of 2007 October 20, 23:54:37
UT. The magnitude is calibrated relative to GSC 0247201072 (GSC1.2) with
a magnitude of 13.54. The afterglow magnitude is consistent with an
earlier observation by Xin et al. (GCN 6956) as well as with a later
observation by Im et al. (GCN 6970).
The AAVSO thanks the Curry Foundation for their continued support of the
AAVSO International High Energy Network.
[GCN OPS NOTE(23oct07): Per submiter's request, "6979" was changed to "6949"
in th 3rd line.]
GCN Circular 6984
Subject
GRB 071020: BTA spectroscopy
Date
2007-10-24T15:00:41Z (18 years ago)
Edited On
2024-11-18T10:10:49Z (7 months ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
T. A. Fatkhullin, V. V. Sokolov (SAO-RAS Nizhnij Arkhyz), S. Guziy
(Nikolaev St. Univ.), A. de Ugarte Postigo (ESO Santiago), D.
Pérez-Ramírez (Univ. de Jaén and U. Leicester), J. Gorosabel, M. Jelínek
and A. J. Castro-Tirado (IAA-CSIC Granada), on behalf of a larger
collaboration, report:
"Following the detection of GRB 071020 by SWIFT (Holland et al. GCN
Circ. 6949) we obtained optical spectroscopy with the 6.0m BTA
telescope (+SCORPIO) of the SAO-RAS. In spite of poor weather
conditions (dense cirrus) we managed to get 4 x 1200s spectra of the
proposed optical afterglow (Schaefer et al. GCN Circ. 6948). The data
were taken on Oct 21.05 U.T. (i.e. 18 hr after the event), with the VPHG
400 grism (range 3700-9000 A).
We identify absorption lines from Fe II (2344, 2586 and 2600) and
possibly C IV (1548-1550) and Fe II (1608), at z = 2.142 ± 0.002. This
confirms the lower limit to the GRB 071020 redshift derived from VLT
spectroscopy (Jakobsson et al., GCN Circ. 6952). Moreover, we do not
see any flux drop in the OA spectrum around 4300 A as the VLT spectrum
may suggest. However, there are indications of a flux drop at ~3870A but
the low S/N ratio in this range prevents us to draw any further
conclusion."
This message can be quoted.
GCN Circular 7006
Subject
GRB071020, optical upper limit
Date
2007-10-26T12:37:21Z (18 years ago)
From
Eri Sonoda at U of Miyazaki/Japan <sonoda@astro.miyazaki-u.ac.jp>
R. Hara, E.Sonoda, H.hayasi, N.Ohmori, K.Kono H. Tanaka, M.Yamauchi
(University of Miyazaki)
We have observed the field covering the error circle of
GRB071020 (GCN 6954, J. Tueller et al.) with
the unfiltered CCD camera on the 30-cm telescope at
University of Miyazaki.
The observation was started 15:29:35 UT, ~507 min.
after the Swift trigger time.
We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog,there is no new source
at the reported position (GCN 6948, B.E.Schaefer et al.
GCN 6949, S.T.Holland et al. GCN 6978, P. Chandra et al.)
the upper limits are as follows:
--------------------------------------------------------------
Start(UT) End(UT) Num. of frames Limit (mag.)
--------------------------------------------------------------
15:31:27 15:31:57 1 ~16.5
15:31:27 16:24:39 20 ~17.0
---------------------------------------------------------------
GCN Circular 7026
Subject
GRB 071020: MITSuME Akeno optical observations
Date
2007-10-31T11:38:14Z (18 years ago)
From
Nobuyuki Kawai at Tokyo Tech <nkawai@hp.phys.titech.ac.jp>
T. Ishimura, Y. Yatsu, T. Shimokawabe, N. Kawai (Tokyo Tech) and
M. Yoshida (NAOJ) report on behalf of the MITSuME collaboration:
We observed the field of GRB 071020 (Holland et al. , GCN6949) with
the 3-color 50cm MITSuME Telescope at Akeno, Japan from UT 16:21 to
UT 19:53 on Oct. 20, 9.3 hours after the trigger.
In the co-added images of Ic and Rc bands, we detected the optical
afterglow reported by Schaefer et al. (GCN 6948). Photometric
calibration was done using the USNO-B1.0 (Ic-band) and NOMAD (g'- and
Rc-bands) catalogs. The results are following:
Filter start end Exposure Mag
------------------------------------------------------
g' 16:21:13 19:53:55 149 x 60s >21.1 (3 sigma upper limit)
Rc 16:21:13 19:53:55 149 x 60s 21.2 +/- 0.3
Ic 16:21:13 19:53:55 149 x 60s 19.8 +/- 0.3
------------------------------------------------------
GCN Circular 7146
Subject
GRB071020: optical observations
Date
2007-12-11T22:46:19Z (17 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
S. Sergeev, V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:
We observed the optical afterglow (Schaefer et al. GCN 6948) of GRB071020
(Tueller et al. GCN 6954) in I and B bands on Oct.10-11 between (UT)
23:51:34 - 01:11:47 with AZT-8 telescope of CrAO. We detected the afterglow
in I-band, and not detected it in B-band. Based on SDSS stars (Cool et al.
GCN 6950) RA=119.66618, Dec=32.84706; RA=119.68899, Dec=32.84803;
RA=119.66782, Dec=32.85465 we estimated brightness of the optical
afterglow on a stacked images:
T0+, Exposure, Filter, mag., UL
(mid time)
0.730 d 12x90 s I 20.5 +/-0.3 20.5
0.728 d 12x180 s B n/d 21.0
The message may be cited.