GRB 051021

D.K. Sahu, G. Pandey, P. Bama and N.K. Chakradhari (Indian Institute of
Astrophysics, Bangalore,India) communicate on behalf of a larger Indian
collaboration:

We observed the error box of the HETE trigger 3947 in Bessell R and I
filters with the 2-m Himalayan Chandra Telescope, Hanle, India, between
20:25 UT and 21:00 UT, 2005 October 21 (about 7 hours after the burst).
We could clearly detect the OT of GRB 051021 reported by Fox et al. (GCN
4120
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 ) with effective exposures of 600s (2x300s) in R and 900s (3x300s) in
I band.  The preliminary magnitudes for the OT, estimated using the
calibration provided by Henden (GCN 4184
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 ) are as follows:

Filter    Mean Mid-UT     Magnitude
  R          20:43      21.51+/-0.15
  I          20.43      20.93+/-0.10

This message may be cited.

Kuntal Misra (ARIES, Nainital) and Atish P. Kamble (Raman Research 
Institute, Bangalore) on behalf of a larger Indian GRB collaboration

We observed the field of GRB 051021 (HETE trigger 3947) using the 104 cm 
reflector telescope at ARIES, Nainital. We do not find any new source upto 
a limiting magnitude of 21 in our combined (exposure 3*300 sec) R band 
images on October 22.675 UT with respect to five nearby USNO-A2.0 stars.

This message may be cited.

M. Nysewander, C. Macleod, D. Reichart, A. Crain, A. Foster report on
behalf of the UNC team of the FUN GRB Collaboration:

Under the control of Skynet, PROMPT observed the localization of GRB 051021
(Yoshida et al., GCN 4116
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 ; Fox et al., GCN 4120
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 ) beginning 12.9 hours after
the burst, in Rc and Ic simultaneously.

We do not detect the afterglow of the burst.  In two 90 x 60 sec
integrations of mean epoch 14.2 hours after the burst, we measure 3-sigma
limiting magnitudes of Rc = 20.7 and Ic = 20.4 based on 5 USNO-B1.0 stars.

PROMPT is still being built and commissioned.

D. Reichart reports on behalf of the UNC team of the FUN GRB Collaboration:

Cobb & Bailyn (GCN 4142
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 ) are correct.  The correct J magnitude at 12.3
hours after the burst is 20.3 +/- 0.2 mag.

Using 4.1m SOAR, we observed the afterglow in BVRIYJHKs.  We will report on
the SFD in a forthcoming GCN.

B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 051021
(GCN 4116
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 , Yoshida et al.) with a mid-exposure time of
2005-10-22 02:53 UT, which is ~13.5 hours post-burst.
Total summed exposure times amounted to 36 minutes in I and 30 
minutes in J.

At the position of the reported afterglow (GCN 4120
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 , Fox et al.), an 
object is marginally detected in our I-band images.  The preliminary 
magnitude of this object is determined to be I = 22.0 +/- 0.4, in 
comparison with several nearby USNO B1.0 stars.

The afterglow candidate is not, however, detected in the J-band.  Using 
several 2MASS comparison stars, the limiting magnitude of this image 
is determined to be J > 19.9 +/- 0.1.  

There is an object near to the position of the afterglow candidate 
(at RA = 1:56:35.6, Dec = 9:04:26.2) that is measured in our image
to have a magnitude of J = 17.2 +/- 0.1.  This object is below the 
detection limits of 2MASS, so it is not detected in the 2MASS 
images (though it is present in the USNO B1.0 survey).  Possibly, this is 
the object reported by Haislip et al. (GRB 4127).  Therefore, in agreement 
with Cenko et al. (GCN 4140
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 ), there is not yet clear evidence 
to suggest that this is a high redshift event.

S. Bradley Cenko, Chris Conselice, Kevin Bundy, (Caltech), Derek B. Fox
(Penn State), and Edo Berger (Carnegie), report on behalf of the
Caltech-NRAO-Carnegie GRB collaboration:

"We have imaged the field of GRB 051021 (Yoshida et al., GCN 4116
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 ) with
the Wide Field Infrared Camera mounted on the Palomar 200" Hale Telescope.
Our images consisted of 9 x 120 s exposures taken in the Ks filter at a
mean epoch of approximately 22 October 5:24 UT (~ 16 hours after the
burst).  We find at best a marginal (< 3-sigma) detection at the location
of the OT (Fox et al., GCN 4120
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 ).  Our 3-sigma limiting magnitude,
calculated with respect to several 2mass stars in the field, is
approximately Ks > 19.0.

We note that under the standard afterglow model, our result is
inconsistent with the J-band detection reported by Haislip et. al (GCN
4127
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 ), and therefore calls into question the interpreration of GRB 051021
as a high redshift event."

J. Eastman, D. L. Depoy (Ohio State U.), A. P. Crotts, & D. J. Beirne
(Columbia U.) observed the afterglow (Fox et al., GCN 4120
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 ) of
HETE GRB 051021 (Yoshida et al., GCN 4116
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 ; Olive et al., GCN 4124
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 )
in the R band using the MDM 1.3m, and in SDSS r using the MDM 2.4m.
On Oct. 22 04:45 UT, 15.4 hours after the burst, they report a 5-sigma
upper limit of R > 23.0.  Compared with the Lulin measurement of R=19.8
at 2.5 hours (Hsieh et al., GCN 4123
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 ), this indicates a mean temporal
decay index steeper than -1.6, possibly a jet break.  In combination
with the bright near-IR detection by Haislip et al. (GCN 4127
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 ), J=17.16
at 12.4 hours, and if the decay index between 12.4 and 15.4 hours is
not steeper than -3.5, the implied R-J color is greater than 5, which
requires a high redshift.

P. J. Brown (PSU), D. Fox (PSU), M. Trippico (GSFC-SSAI),
J. Nousek (PSU),  & N. Gehrels (GSFC)
on behalf of the Swift/UVOT team report:

The Swift-UVOT began observing the field of
GRB 051021 (HETE Trigger H3947; Yoshida et al. GCN 4116
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 )
at 2005-10-21 16:28:27, about 3 hours after the burst.

No source is detected at the position of the optical
counterpart found by Fox, McNaught, & Peterson (GCN 4120
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 )
in any of our 6 filters down to the following 3-sigma
upper limits:

Filter  T_range(hours)  Exp(sec)  3sigUL

V       3.36-8.34       1988      20.2
B       5.30-6.71       1304      21.1
U       5.04-5.29        900      20.5
W1      4.79-5.04        900      20.8
M2      3.61-3.80        900      20.9
W2      3.11-6.96       1800      21.7

Where T_range is time post-trigger.

E.Sonoda,S.Maeno,Y.Tokunaga, M.Yamauchi
(University of Miyazaki)


"We have observed the field covering the SXC error box of
GRB051021(HETE trigger 3947; trigger time 13:21:5 UT ) with the
unfiltered CCD camera on the 30-cm telescope at University of
Miyazaki.The observation was started 13:22:30 UT on Oct.21.
We have compared our image with the USNO A2.0 catalog .
Preliminary analysis shows there is no new source brighter than 14.3 mag.
at the position reported by D.B.Fox et al.(GCN4120
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 ). "

J. Haislip, M. Nysewander, E. Cypriano, D. Reichart, M. Bayliss report on
behalf of the UNC Team of the FUN GRB Collaboration:

The SOAR-4.1m Telescope at CTIO began imaging the afterglow of the HETE GRB
051021 (Yoshida et al., GCN 4116
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 ; Fox et al., GCN 4120
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 ) at 01:38:51 UT,
12.3 hours after the burst in YJHKs.

We detect the afterglow at a magnitude of J = 17.16 +- 0.06 based on three
2MASS stars at a mean time of 01:47:19.2 UT, 12.4 hours after the GRB.

J. Racusin, J. Kennea, D. Morris, D. Fox, D. Burrows (PSU), N. Gehrels 
(GSFC) on behalf of the Swift XRT team:

XRT began observing GRB051021 (Yoshida et al., GCN 4116
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 ) at 16:28:28 UT, 
approximately 3 hours after the HETE trigger.  From the first 2 orbits of 
data, we detect an uncatlogued fading X-ray source at:

RA(J2000):   01:56:36.4
Dec(J2000): +09:04:06.3

with an estimated uncertainty of 4 arcseconds (90% containment).

This position is 4.3 arcminutes from the HETE position reported by Yoshida 
et al.(GCN 4116
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 ), and 2.7 arcseconds from the optical afterglow position 
reported by Fox et al.(GCN 4120
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 ).

At the time of these observations using 4.7 ks of data, the measured flux 
was 2.7x10^-12 ergs/cm^2/s.  Further observations are necessary to measure 
the lightcurve decay slope.

J-F Olive, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;

M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka,
Y. Nakagawa, T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki,
S. Sugita, M. Suzuki, T. Tamagawa, K. Tanaka, and A. Yoshida, on behalf
of the HETE WXM Team;

N. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek,
J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,
R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and
HETE Optical-SXC Teams;

M. Boer, J-P Dezalay, and K. Hurley, on behalf of the HETE FREGATE
Team;

report:

We have analyzed the full FREGATE+WXM data for HETE trigger H3934
(GRB051021.56).

The 30-400 keV light curve has two sharp peaks, separated by about 10 s,
superposed on a gentler rise-and-fall. The burst had a T90 duration of 38s
in the 7-40 keV band, and of 27s in the 30-400 keV band.  Emission in the
2-25 keV band appears to continue for at least 90s post-trigger, mostly
below 10 keV.

The integrated spectrum is well-fit by a cutoff power-law function.  The
best-fit parameters are:

alpha = -1.16 --- 90% confidence interval is [-1.25 -1.06]
Epeak = 94.2  --- 90% confidence interval is [76.7 , 111.7]

The 2-30 keV fluence is 3x10^-6 erg/cm2, while the 30-400 keV fluence is 
6 x 10^-6 keV.  Since the ratio S(2-30)/S(30-400) is 0.41, this event is
classified as an X-Ray Rich GRB.

The pseudo-redshift estimated for this burst is pz = 1.4.

A light curve, a skymap, and spectral information for this event are
provided at the following URL:

http://space.mit.edu/HETE/Bursts/GRB051021

GRB 051021 : optical afterglow observation at Lulin

H.H. Hsieh (IfAUH), M.S. Chang, K.Y. Huang, W.H. Ip (NCU), Y. Urata
(RIKEN), Y. Qiu (BAO) on behalf of the East Asian collaboration
report:

 The R-band observations of GRB 051021 (Yoshida et al., GCN 4116
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 ) were
taken by Lulin 1-m telescope, Taiwan.  The optical afterglow reported
by Fox et al.(GCN 4120
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 ) was detected clearly in our R-band
images. Compared with USNOB stars, the R band magnitude of afterglow
is about 19.8 at 15.859 UT (~ 2.48 hrs after the burst).

Further observations are on going. 
This message may be cited.

P. Tristram (Univ. of Canterbury, New Zealand),S. Guziy,
A. de Ugarte Postigo, Shashi. B. Pandey, A. J. Castro-Tirado,
M. Jelinek, J. Gorosabel (IAA-CSIC, Granada, Spain),
and Ph. Yock (Univ. of Auckland, New Zealand)

report:

"We have observed the region centered around  the HETE error box
for GRB 051021 (Yoshida et al.2005, GCN 4116
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 ) with
0.6 m  telescope at Mount John observatory (New Zealand), starting
on October 21 ( 14:10 UT, 45 minutes after the GRB). We confirm the
optical candidate reported by Fox et al. (GCN, 4120)."

Further observations are in progress.

This massage can be cited.

H. Swan (U Mich), T.A. McKay (U Mich), D.A. Smith (Guilford), B. 
Schaefer (Louisiana State), E.S. Rykoff (U Mich), F. Yuan (U Mich), 
report on behalf of the ROTSE collaboration:

ROTSE-IIIa, located at Siding Spring Observatory, Australia, responded 
to GRB 051021 (HETE trigger 3947). The first image was at 13:22:28.4 UT, 
31.8 s after the burst (6.6 s after the GCN notice time). The unfiltered 
images are calibrated relative to USNO A2.0. We confirm the presence of 
the source detected by Fox et. al. GCN # 4120.  We observe the source to 
rise to 16.9 magnitude, at about 180 seconds, and then fade by half a 
magnitude over a period of 150 seconds.

This source is not visible in DSS (second epoch), 2MASS or the MPChecker 
database.

Continuing observations are in progress.

>

D.B. Fox (Penn State), with R. McNaught and B. Peterson (RSAA/ANU),
report on behalf of a larger collaboration:

"We have observed the HETE localization region for GRB051021 (Yoshida
et al., GCN 4116
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 ) with the 40-inch telescope at Siding Spring
Observatory, in a sequence of R-band exposures beginning at 13:48:48
UT (26m51s after the burst).  Comparison of a coadded image with mean
epoch 14:34:33 (1h12m post-burst) to the Digitized Sky Survey reveals
the presence of a new R~18.5 mag source, at coordinates:

     R.A. 01:56:36.39, Dec +9:04:03.7  (J2000)

with a coordinate uncertainty, relative to USNO-B1.0 catalog
astrometry, of <0.5".  Inspection of our individual images suggests
fading of the source over the ~1 hour span of our observations.
However, in the absence of a more sophisticated reduction of these
data it is not possible to make a firm conclusion as to variability at
this time.  Moreover, the presence of a cosmetic defect at the source
position in one image introduces significant uncertainty to our
mean photometric estimate, above.

We suggest that this source may be the optical afterglow of
GRB051021."

A. Yoshida, G. Ricker, J-L. Atteia, N. Kawai, D. Lamb, and S. Woosley,
on behalf of the HETE Science Team;
 
M. Arimoto, T. Donaghy, E. Fenimore, M. Galassi, C. Graziani,
N. Ishikawa, A. Kobayashi, J. Kotoku, M. Maetou, M. Matsuoka,
Y. Nakagawa, T. Sakamoto, R. Sato, T. Shimokawabe, Y. Shirasaki,
S. Sugita, M. Suzuki, T. Tamagawa, and K. Tanaka, on behalf of the HETE
WXM Team;
 
N. Butler, G. Crew, J. Doty, G. Prigozhin, R. Vanderspek,
J. Villasenor, J. G. Jernigan, A. Levine, G. Azzibrouck, J. Braga,
R. Manchanda, and G. Pizzichini, on behalf of the HETE Operations and
HETE Optical-SXC Teams;
 
M. Boer, J-F Olive, J-P Dezalay, and K. Hurley, on behalf of the HETE
FREGATE Team;
 
report:

The HETE FREGATE, WXM, and SXC instruments detected GRB 051021
(=H3947) at 13:21:57 UT (48117 SOD) on 21 October 2005.  The
WXM flight localization was first reported in a GCN Notice issued 
at 13:22:11 UT, which was 14s after the burst trigger.

Ground analysis of the WXM data produced a refined WXM localization that
was issued in a GCN Notice at 14:25:34 UT.  This ground WXM localization
can be expressed as a circle of 7.5 arcminutes radius (90% confidence),
centered at

  R.A. = 01h 56m 24s ; Dec. = +09d 07' 05" (J2000).

The SXC detected this event in its Y camera. Ground analysis of the SXC
data therefore produced a 1-dimensional location.  The intersection of
this location with the WXM ground location was issued in a GCN Notice at
14:59:49 UT.  This location can be expressed as a box with corners:

 R.A. = 01h 56m 01.92s ; Dec. = +09d 02' 02.4"
 R.A. = 01h 56m 54.00s ; Dec. = +09d 05' 16.4"
 R.A. = 01h 56m 54.72s ; Dec. = +09d 07' 22.8"
 R.A. = 01h 59m 57.12s ; Dec. = +09d 03' 46.8" (J2000).

Further analysis is in progress.