GRB 071021
GCN Circular 6958
Subject
GRB 071021: Swift detection of a burst
Date
2007-10-21T09:56:46Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
T. Sakamoto (NASA/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB) and
S. D. Vergani (DIAS-DCU) report on behalf of the Swift Team:
At 09:41:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 071021 (trigger=294974). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 340.636, +23.707 which is
RA(J2000) = 22h 42m 33s
Dec(J2000) = +23d 42' 24"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). As with most 64 second image triggers,
there is no obvious variation in the count rate light curve.
The XRT began observing the field at 09:43:44 UT, 130 seconds after the
BAT trigger. XRT found a bright, uncatalogued X-ray source
located at RA, Dec 340.6445, +23.7185 which is
RA(J2000) = 22h 42m 34.6s
Dec(J2000) = 23d 43' 06.5"
with an uncertainty of 6.0 arcseconds (radius, 90% containment).
This location is 50 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 3.2e-09 erg/cm2/s (0.2-10 keV).
UVOT is still in engineering mode after the gyro restorations, so there
will be no data products for this trigger.
Burst Advocate for this burst is T. Sakamoto (takanori 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 6959
Subject
GRB 071021: Faulkes Telescope South optical candidate
Date
2007-10-21T10:47:13Z (18 years ago)
From
Andrea Melandri at Liverpool John Moores U <axm@astro.livjm.ac.uk>
C. Guidorzi (U. Bicocca & INAF-OAB), A. Melandri, I.A. Steele,
R.J. Smith, C.J. Mottram, M.F. Bode, D. Carter, S. Kobayashi,
D.F. Bersier, C.G. Mundell (Liverpool JMU), A. Gomboc (U. Ljubljana),
P. O'Brien, E. Rol, N. Bannister (U. Leicester) report:
The 2-m Faulkes Telescope South robotically followed up GRB071021
(Sakamoto et al., GCN Circ. 6958) beginning 258 seconds after the GRB
trigger time (UT 09:41:33).
We detect a fading uncatalogued source at
RA = 22:42:35.41
Dec = +23:43:08.9
with un uncertainty of 0.7 arcsec on both coordinates. This position
is 11.4 arcsec from the centre of first XRT error circle (Sakamoto et
al., GCN Circ. 6958).
We measure a magnitude of R = 17.8 +/- 0.3 for a 3x10 seconds coadded
frame, from 258 to 308 seconds after the trigger time. In subsequent
images the source clearly faded.
Magnitudes are calibrated with respect to R2 mag of several nearby
USNO-B1 objects. Observations are still ongoing.
GCN Circular 6961
Subject
GRB 071021 : Lulin R-band limit
Date
2007-10-21T15:12:26Z (18 years ago)
From
Kuiyun Huang at ASIAA <ljhuang@asiaa.sinica.edu.tw>
W.S. Hsiao, H.C. Lin , Y.H. Lee, Y. Urata, K.Y. Huang on behalf of the
EAFON team
The B,V,R band observations for GRB 071021 field with Lulin 1-m
telescope started at 1.38 hours after the burst. No source was found
at XRT position (Sakamoto et al.; GCN 6958) and optical candidate
position (Guidorzi et al.; GCN 6959) in our combined images. The
R-band limiting magnitude, compared with several USNOB stars, is about
20.4 at 1.87 hours after the burst . This result suggests that the
fading optical source reported by Guidorzi et al. (GCN 6959) is the
optical afterglow of GRB 071021.
this message may be cited
[GCN OPS NOTE(22oct07): Per author's request, "Golenetskii et al.; GCN 6959"
was changed to "Guidorzi et al.; GCN 6959".]
GCN Circular 6962
Subject
GRB 071021: Xinglong TNT optical Upper Limit
Date
2007-10-21T17:17:44Z (18 years ago)
From
L.P. Xin at NAOC <xlp@bao.ac.cn>
L.P. Xin, M. Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng,
J. Wang and W.K. Zheng on behalf of EAFON report:
We have imaged the field of GRB 071021 (T. Sakamoto, et al.;
GCN 6958) with the TNT 0.8m telescope at Xinglong
Observatory started from 09:55:06.5 UT, 813.8880 after
the burst. A series of White and R band images were
obtained, no new source was found in our combined
image within the error region of the XRT
(T. Sakamoto, et al.; GCN 6958) and the location reported
by C. Guidorzi et al (GCN 6959)
The 3-sigma limit derived from
USNO-B1.0 R2 mag were:
------------------------------------
Band Mid time Exp time Limit Mag
White 0.72 hours 40*20s 20.32
R 1.38 hours 12*300s 20.85
R 3.25 hours 16*600s 21.69
This message may be cited.
[GCN OPS NOTE(21oct07): Per author's request, the names for the 3 references
were changed T. Sakamoto, T. Sakamoto, and C. Guidorzi.]
GCN Circular 6963
Subject
GRB 071021: Swift-XRT Team refined analysis
Date
2007-10-21T17:18:52Z (18 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page (U Leicester), N. Gehrels (NASA/GSFC) and T. Sakamoto
(NASA/UMBC) report on behalf of the Swift-XRT team:
We have analysed three orbits of Swift-XRT data obtained for GRB 071021
(Sakamoto et al. GCN Circ. 6958), totalling 1.7 ks of Windowed Timing (WT)
data and 5.3 ks of Photon Counting (PC) data. Using the PC data we derive
a refined position of RA, Dec = 340.64311, +23.71808, which is equivalent
to
RA(J2000) = 22 42 34.35
Dec(J2000) = +23 43 05.1
with an estimated error radius of 3.9 arcsec (90 percent containment).
This is 4.8 arcsec from the onboard XRT position given by Sakamoto et al.
in GCN Circ. 6958). The position is also 15.1 arcsec from the Faulkes
Telescope South optical candidate (Guidorzi et al., GCN Circ. 6959) and
therefore not consistent with it.
The X-ray light-curve is initially quite flat, remaining at around 40-50
count s^-1 until 230 seconds after the trigger. There follows a very steep
decay, until about 700 seconds post-trigger, when a series of strong
flares are seen; this behaviour continues into the second orbit, with the
third orbit showing the afterglow emission has decayed further.
There is spectral evolution during the initial light-curve, although the
WT data before the steep decay (135-245 seconds) can be modelled as an
absorbed power-law, with Gamma = 2.12 +/- 0.09 and a total absorbing
column of NH = (1.8 +/- 0.2)e21 cm^-2, considerably in excess of the
Galactic value of 4.8e20 cm^-2. The 0.3-10 keV observed (unabsorbed) flux
during this time is 1.3e-10 (1.9e-10) erg cm^-2 s^-1.
Because of the flaring activity, it is not feasible accurately to predict
a count-rate at 24 hours.
This circular is an official product of the Swift-XRT team.
GCN Circular 6964
Subject
GRB 071021: retraction of Faulkes Telescope South candidate
Date
2007-10-21T18:17:51Z (18 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi (U. Bicocca & INAF-OAB), A. Melandri, I.A. Steele,
R.J. Smith, C.J. Mottram, M.F. Bode, D. Carter, S. Kobayashi,
D.F. Bersier, C.G. Mundell (Liverpool JMU), A. Gomboc (U. Ljubljana),
P. O'Brien, E. Rol, N. Bannister (U. Leicester) report:
The fading optical candidate reported in our previous message
(Guidorzi et al., GCN Circ. 6959) has been found to be spurious
due to technical problems.
We apologise for the inconvenience caused.
GCN Circular 6966
Subject
GRB 071021, Swift-BAT refined analysis
Date
2007-10-21T19:33:04Z (18 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+472 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 071021 (trigger #294974)
(Sakamoto, et al., GCN Circ. 6958). The BAT ground-calculated position is
RA, Dec = 340.573, 23.764 deg, which is
RA(J2000) = 22h 42m 17.6s
Dec(J2000) = 23d 45' 49"
with an uncertainty of 3.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.
The mask-weighted light curve shows a slow rise starting at ~T-30 sec and
peaking around T+85 sec. The remaining portion of the lightcurve is
consistant with either a low-level constant emission out to ~T+225 sec or
with a decline to background around T+150 sec and then another weak peak
from ~T+180 to ~T+220 sec. This latter interpretation is consistant with a
small flare in the XRT afterglow lightcurve around T+220 sec.
T90 (15-350 keV) is 225 +- 10 sec (estimated error including systematics).
The time-averaged spectrum from T-31.4 to T+252.2 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.70 +- 0.21. The fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+87.32 sec in the 15-150 keV band
is 0.7 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
This burst has several characteristics which are typical of high
redshift bursts. Its duration is long (T90 = 225 sec) with relatively
few (two) significant peaks. The 1-s peak flux is < 1.0 ph/cm2/s
and the power-law photon index (1.70) is < 2.
GCN Circular 6967
Subject
GRB 071021: possible high-z burst
Date
2007-10-21T22:08:21Z (18 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori@milkyway.gsfc.nasa.gov>
T. Sakamoto (GSFC/UMBC), N. Gehrels (GSFC) and Kim Page (U. Leicester)
We point out that GRB 071021 has several signatures of high redshift.
As pointed out in GCN 6966, it has BAT high-redshift indicators
(Sakamoto et al. 2007 in prep.) as follows:
- long duration T90 = 225 sec
- relatively few (two) significant peaks
- peak flux (1 s) < 1.0 ph/cm2/s
- power-law photon index (1.70) < 2
Since May 2007, only this burst and GRB 071018 (GCN 6933) have
satisfied all four indicators. GRB 071021 also has an X-ray
afterglow lightcurve with strong late-time flares (GCN 6963; see
http://gcn.gsfc.nasa.gov/gcn/other/071021_xrtlc.gif) reminiscent
of high-redshift burst GRB 050904. It also has optical observations
without detection (GCN 6961, 6962).
Deep IR observations are strongly encouraged.
GCN Circular 6968
Subject
GRB 071021: optical and NIR observations
Date
2007-10-22T00:31:34Z (18 years ago)
Edited On
2024-11-18T10:08:01Z (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>
A. J. Castro-Tirado (IAA-CSIC Granada), A. de Ugarte Postigo (ESO
Santiago), M. Jelínek, J. Gorosabel, A. Marín Fernández de Capel
(IAA-CSIC), C. Abia (Universidad de Granada), D. Pérez-Ramírez (Univ. de
Jaén & U. Leicester), D. Malesani (DARK/NBI), S. Guziy (Univ. of
Nikolaev) and R. Oreiro (IAC), on behalf of a larger collaboration,
report:
"Following the detection of GRB 071021 by SWIFT (Barthelmy et al. GCNC
6958) we have obtained JHK-band observations (300s each) with the 3.5m
Telescopio Nazionale Galileo at Observatorio del Roque de los Muchachos
in La Palma and optical observations with the 2.5m Nordic Optical
Telescope (1200s, R-band)
and with the 1.5m telescope (3960s, I-band) at Observatorio de Sierra
Nevada.
The NIR frames were obtained starting on 21.872 Oct (i.e. 11.25 hr after
the BAT trigger).
Within the XRT error box (Page et al. GCNC 6963) there seems to be an
indication of a faint source at RA(J2000) = 22:42:34.31 Dec(J2000)=
+23:43:06.5 (+/- 1"). The object seems to be barely detected in the -H
and -K bands, but not in J, indicating a highly obscured object or a
very high-z (~10) event, supporting in the latter case the SWIFT high-z
indications (Sakamoto et al. GCNC 6967).
A finding chart is available at:
http://www.iaa.es/~deugarte/GRBs/071021/GRB071021_JHK.jpg
Further analysis is ongoing.
Additional NIR observations are needed to confirm the reality of this
source and whether this is the NIR afterglow to GRB 071021."
[GCN OPS NOTE(22oct07): Per author's request, the coordinates were
corrected from "RA(J2000) = 10:58:11.3 Dec(J2000)=+53:50:56" to
"RA(J2000) = 22:42:34.31 Dec(J2000)=+23:43:06.5".]
[GCN OPS NOTE(24oct07): Per author's request, "U Leceister" was changed to
"U. Leicester".]
GCN Circular 6971
Subject
GRB 071021: correction to GCNC 6968
Date
2007-10-22T01:09:18Z (18 years ago)
Edited On
2024-11-18T09:53:29Z (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>
A. J. Castro-Tirado (IAA-CSIC Granada), A. de Ugarte Postigo (ESO
Santiago), M. Jelínek, J. Gorosabel, A. Marín Fernández de Capel
(IAA-CSIC), C. Abia (Universidad de Granada), D. Pérez-Ramírez (Univ. de
Jaén & U Leceister), D. Malesani (DARK/NBI), S. Guziy (Univ. of
Nikolaev) and R. Oreiro (IAC), on behalf of a larger collaboration,
report:
"We apologize for the incorrect coordinates reported on GCNC 6968,
regarding GRB 071021. The right ones (J2000 ± 0.5") are:
RA = 22:42:34.31
Dec= +23:43:06.5
This message can be quoted."
GCN Circular 6972
Subject
GRB 071021: Z-band detection
Date
2007-10-22T02:18:51Z (18 years ago)
From
Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center <malesani@astro.ku.dk>
D. Malesani (DARK), S. Piranomonte (INAF/OARm), G. Tagliaferri, G.
Chincarini, S. Covino (INAF/OABr), F. Fiore, L. Stella (INAF/OAR),
report on behalf of the MISTICI collaboration:
We observed the field of GRB 071021 (Sakamoto et al., GCN 6958) with the
8.2m VLT+FORS2 equipped with the z_Gunn filter (effective wavelength:
9100 A; FWHM: 1300 A).
In a coadded image totalling 15 min exposure, we see a weak source at
the coordinates provided by Castro-Tirado et al. (GCNs 6968, 6971).
Our detection would suggest a redshift less than roughly 6.5.
A finding chart is poste at:
http://www.astro.ku.dk/~malesani/GRB/071021/071021_finder.jpg
We acknowledge excellent support from the ESO staff, particularly Hugues
Sana.
GCN Circular 6973
Subject
GRB 071021: Magellan R-band observation
Date
2007-10-22T02:29:40Z (18 years ago)
From
Edo Berger at Princton U <eberger@astro.princeton.edu>
E. Berger (Princeton/OCIW) and R. Covarrubias (LCO) report:
"We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the
R-band using the LDSS3 instrument on the Magellan/Clay telescope. In a
coadded image of 540 sec we do not detect any objects within the XRT error
circle to a 3-sigma limit of R>23.1 mag. Further observations in R and I
band are in progress."
GCN Circular 6974
Subject
GRB 071021: Magellan i-band observation
Date
2007-10-22T03:51:39Z (18 years ago)
From
Edo Berger at Princton U <eberger@astro.princeton.edu>
E. Berger (Princeton/OCIW) and R. Covarrubias (LCO) report:
"We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the
i-band using the LDSS3 instrument on the Magellan/Clay telescope. In a
coadded image of 1120 sec we do not detect any object within the XRT error
circle to a 3-sigma limit of i>23 mag.
Since no z-band magnitude was reported in GCN 6972 we cannot determine
whether our limits are significantly deeper. However, our non-detection
in r- and i-band appears to indicate a redshift of z~6-6.5 (for i-band
effective wavelength = 7600A and FWHM = 1300A). Further observations are
in progress."
GCN Circular 6975
Subject
GRB071021: MITSuME Okayama Optical Upper Limits
Date
2007-10-22T06:03:35Z (18 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida, K. Yanagisawa, Y. Shimizu, S. Nagayama, H. Toda
(NAOJ), and N. Kawai (Tokyo Tech) report on behalf of the
MITSuME collaboration:
We observed the field of GRB071021 (Sakamoto et al., GCN6958)
with the three-color 50cm MITSuME Telescope at Okayama
Astrophysical Observatory. The observations started at 9:45:30
Oct. 21 UT (3m58s after the trigger). No new point source was
found in the XRT error circle of this burst (Barbier et al.,
GCN6966). The 3-sigma upper limits derived with the USNO B1.0
catalog are followings.
-------------------------------------------------------------
Mid time Exp time G Rc Ic
-------------------------------------------------------------
2007-10-21 9:57:03 20min (60s x 20) >19.4 >19.1 >18.7
2007-10-21 10:48:01 99min (60s x 99) >20.3 >19.6 >19.3
-------------------------------------------------------------
GCN Circular 6976
Subject
GRB 071021: Subaru NIR observation
Date
2007-10-22T08:55:44Z (18 years ago)
From
Nobuyuki Kawai at Tokyo Tech <nkawai@hp.phys.titech.ac.jp>
H. Terada, T.-S. Pyo, K. Aoki, T. Hattori (Subaru Telescope/NAOJ) and
N. Kawai (Tokyo Tech) report on behalf of the Subaru GRB team:
"We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the
K, H, and J-bands using the IRCS instrument on the Subaru Telescope.
We detected the afterglow candidate (Castro-Tirado et al. GCNs 6968,
6971, Malesani et al. GCN 6972) in the K-band image at approximately
K~21 mag (midtime 2007-10-22 05:38 UTC). Further observations are in
progress."
GCN Circular 6980
Subject
GRB 071021: (Relatively shallow) IR non-detections; motivation for optical spectroscopy
Date
2007-10-23T06:05:13Z (18 years ago)
From
Josh Bloom at UC Berkeley <jbloom@astron.berkeley.edu>
J. S. Bloom (UC Berkeley), J. X. Prochaska (UCO/Lick), D. A. Perley
(UC Berkeley), H.-W. Chen (U Chicago), D. L. Starr (UC Berkeley &
LCOGT), M. Modjaz, D. Poznanski (UC Berkeley) report:
"We observed the field of GRB 071021 (Sakamoto et al. GCN 6958) with
PAIRITEL (*) starting at 2007-10-22 04:53 UT in high wind and poor
seeing conditions at Mt Hopkins, Arizona. In the first 1340 second
stack, the IR source noted by Castro-Tirado et al. (GCN 6968/6971) is
not detected to J=18.35 mag, H=16.87 mag, Ks=16.43 (2.5 sigma upper
limit). This is not particularly constraining in light of the deep
Subaru imaging (Terada et al. GCN 6976) at a similar epoch.
We note that despite the z-band detection (Malesani et al. GCN
#6972) the very high-redshift hypothesis of Sakamoto et al. (GCN
6967) is not yet ruled out. In particular, in high z QSO spectra
there can be some transmitted flux (in the z-band filter
transmission) through the Lyman-alpha forest between ~8000 Ang and
8500 Ang (see, e.g., Fan et al. 2006 **) for z > 6.3 sources. So long
as the redshifted Lyman limit at the redshift of the emitting source
is blueward of ~8500 Ang, this light would not be entirely
suppressed. This consideration yields an upper limit:
(1 + z_GRB)*912 Ang < 8500 Ang
z_GRB <~ 8.3
At such redshifts, say z_GRB = 8, all reported long-wavelength
observations to-date would be naturally accommodated:
- the deep non-detections at R and i-band (Berger & Covarrubias,
GCNs 6973,6974), being blueward of 912*[1+z_GRB])
- the faint detection at z-band (GCN 6972) due transmitted flux
between 912*[1+z_GRB] = 8200 and 8500 Ang is allowed (as above)
- the afterglow detections at H and K (GCN 6968; Terada et al. GCN
6976)
- the apparent faintness of J-band flux (GCN 6968) relative to H
and K given the Gunn-Peterson trough would extend to (1 + z_GRB)*1216
Ang =~ 1.1 micron.
All of this assumes that the z-band source is not a foreground
galaxy (in which case a higher-z GRB suggested by Castro-Tirado et
al. is allowed). If indeed the GRB originated from z > 7, we would
expect to see what would resemble emission lines between lam_obs =
912*[1+z_GRB] and ~8500 Ang, motivating the utility of *optical*
spectroscopy of this source. Even without spectroscopy, when final
magnitudes are reported along with filter transmission curves, a full
SED should be illuminating."
This message may be cited.
(*) http://pairitel.org
(**) http://www.journals.uchicago.edu/AJ/journal/issues/
v132n1/205115/205115.web.pdf
GCN Circular 6982
Subject
Possible radio detection of GRB 071021 with the VLA
Date
2007-10-23T13:36:22Z (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 071021 (GCN 6958) using the VLA at a frequency of 8.46 GHz.
The observations were taken at a mean time of 06.11 UT on 23nd Oct 07.
We detect possible radio afterglow of GRB 071021 in agreement with NIR
position (GCN # 6971) and the Swift-XRT afterglow position (GCN # 6963).
Our 3-sigma detection yields the flux value of 149+/-44 uJy at the
following position:
RA(J2000) 22 42 34.25
Dec(J2000) +23 43 06.36
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 6983
Subject
GRB071021: Optical+NIR observations
Date
2007-10-23T19:55:21Z (18 years ago)
From
Paul Price at IfA,UH <price@ifa.hawaii.edu>
P.A. Price (IfA, Hawaii), T. Minezaki (IoA, Tokyo), L. Cowie (IfA,
Hawaii), Y. Yoshii (IoA, Tokyo) and Y. Kakazu (IfA, Hawaii) report:
We observed the candidate optical afterglow of GRB071021 (GCN##6968,
6971,6972) with the robotic MAGNUM telescope + MIPS dual-beam imager.
Some observations were significantly affected by cloud, but images in I,
H and K were obtained through thin clouds. We do not detect any source
in our images at the candidate afterglow position, to the following 3
sigma limits, derived from the USNO-1B and 2MASS catalogues:
Filter midtime(UTC) Exp. time upper limits
I 2007-10-22 6.9h 67min >22.5mag
H 2007-10-22 7.7h 30min >20.4mag
K 2007-10-22 6.1h 33min >19.8mag
Our K-band upper limit is consistent with the detection of the afterglow
in K band reported by Kawai et al. (GCN 6976; K~21 mag at 2007-10-22
05:38 UTC).
This message may be cited.
GCN Circular 6985
Subject
GRB 071021: R-band detection and analysis
Date
2007-10-24T20:23:32Z (18 years ago)
From
Silvia Piranomonte at OAR <piranomonte@mporzio.astro.it>
S. Piranomonte (INAF/OAR), P. D'Avanzo (INAF/OABr), D. Malesani
(DARK), A. Fernandez-Soto ( U.Valencia), G. Tagliaferri (INAF/OABr),
G. Chincarini (U.Bicocca), S. Covino (INAF/OABr), F. Fiore (INAF/OAR),
D. Fugazza (INAF/OABr), L. Stella (INAF/OAR), report on behalf of the
MISTICI collaboration:
We observed the field of GRB 071021 (Sakamoto et al., GCN 6958) with the
8.2m VLT+FORS2 equipped with the R filter (effective wavelength:
6550 A; FWHM: 1650 A).
An eight-minute exposure was obtained on Oct 22.06688 , and a second,
thirty-minute exposure, on Oct 22.99604. A weak source is detected in
both images at the position of the candidate afterglow provided by
Castro-Tirado et al. (GCNs 6968, 6971).
The object has not faded significantly between both epochs, although
the very low S/N (~2) in the first image does not allow for a strong
statement regarding its variability.
Combining our own data and all the available optical-NIR data (GCNs
6962, 6973, 6974, 6975, 6976, 6980, 6983) we have measured a
photometric redshift z~5, but with a 2-sigma confidence interval that
includes all values in the z=[0 ... 5.5] range.
An alternative explanation for all the available data is that of a
strongly reddened afterglow (detected as a fading source in the H- and
K-band images), having taken place in a galaxy at a significantly
lower redshift (detected in our deeper, bluer, R- and z-band
images). This model should be checked via spectroscopy of the putative
host galaxy.
Our R-band images and the results of the preliminary photometric
redshift analysis are posted at:
http://ayalga.uv.es/~fsoto/grb/grb071021/
We acknowledge excellent support from the ESO staff, in particular
Emanuela Pompei and Hugues Sana.
This message may be cited.
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GCN Circular 6993
Subject
GRB071021 : CFHT Ks-band observation
Date
2007-10-25T06:55:17Z (18 years ago)
From
Yuji Urata at Saitama U <urata@crystal.heal.phy.saitama-u.ac.jp>
Y. Urata (Saitama Univ.), K.Y. Huang (ASIAA), W.H. Ip (NCU), and
L. Albert (CFHT/UH) on behalf of EAFON team:
"We have observed the field of GRB 071021 (Sakamoto et al., GCN 6958)
in Ks-band using the WIRCam instrument on the CFHT telescope. We
marginally detected the afterglow (Castro-Tirado et al. GCNs 6968,
6971, Malesani et al. GCN 6972, Terada et al GCN 6976, Piranomonte et
al. GCN 6985). The brightness derived from 2MASS stars is about Ks~21
at the mid time of the stacked image (2007-10-23-05:42). This result
suggests that the NIR afterglow show shallow decay between October 22
and 23. Further analysis and observations are in progress."
This message may be cited.
GCN Circular 7007
Subject
GRB071021: MARGE Optical Limits
Date
2007-10-26T15:23:36Z (18 years ago)
From
Heather Swan at U.of Michigan/ROTSE <hflewell@umich.edu>
H. Swan (U Mich), I. Smith (Rice), C. Akerlof (U Mich), E. Rykoff (UCSB)
and M. Skinner (Boeing) report on behalf of the MARGE collaboration:
The AEOS Burst Camera (ABC) on the AEOS telescope, located at the Maui
Space Surveillance System on Haleakala, observed the field of GRB071021
(Swift trigger 294974 (T. Sakamoto et al, GCN 6958)). The images are
unfiltered 10s exposures that started ~10 minutes after the trigger and
ended ~ 2 hour later. We calibrated our images to the USNO-B1 R2
catalog. We do not see the NIR counterpart observed by A. J.
Castro-Tirado et al. (GCN 6968), down to the following limiting
magnitudes. We have not corrected for the galactic extinction, which is
E(B-V)= 0.074 mag, according to the NED Extinction calculator.
start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
09:51:24.7 09:57:32.2 367.5 22.6 591.7 Y
09:51:24.7 12:09:06.9 8262.3 23.7 591.7 Y
The ABC is an unfiltered camera, with enhanced sensitivity in the red
end of the spectrum. This sensitivity to the red end of the spectrum
allows us to see high (z < 6) bursts. The relatively deep upper limits
we have obtained may assist efforts to better determine the redshift for
this unusual event.