GRB 031026

D. Budi(University of Tokyo), T. Nakamura(NAOJ), F. Yoshida(NAOJ), 
T. Aoki and Y. Urata on behalf of KISO GRB Team report;

" We have observed the entire HETE-2 error circle of GRB031026 (=
H2882) with Kiso observatory 1.05 m Schmidt telescope (Kiso
Observatory, Institute of Astronomy, the University of Tokyo). We
obtained Rc-band data sets (300 sec x 3 frames), starting at Oct 26
11:28 UT. The limiting magnitude for each images is about 18 mag.
Comparison with DSS II red images, no new object was detected down to
the limiting magnitude.

Further observation and analysis are in progress."

This message may be cited.

M.C. Nysewander, J.A. Moran, D. Reichart (Univ. of North Carolina) & M.
Schwartz (Tenagra Observatories) on behalf of the FUN GRB collaboration
report:

        We began observations in Ic of the error box of HETE trigger 2882
(GRB 031026) at 09:30:10 UT (3.9 hrs after the burst) with the 32-inch
Tenagra II telescope.  99% of the error box was covered in four pointings,
with a total integration time of 1350s per pointing.

        Comparison to the POSS2 Red & IR images yields no candidates down
to the approximate limiting magnitude of the plates, which we estimate to
be Ic ~ 19.

GRB031026 (=H2882): A Long, Hard Spectrum Burst Localized by HETE

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

T. Donaghy, C. Graziani, E. Fenimore, M. Galassi, M. Matsuoka, T. 
Sakamoto, Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Torii, A. Yoshida, 
Y. Nakagawa, R. Satoh, Y. Urata, T. Yamazaki and Y. Yamamoto, on 
behalf of the HETE WXM Team;

G. Crew, J. Doty, A. Dullighan, G. Prigozhin, R. Vanderspek, J. 
Villasenor, J. G. Jernigan, 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, C. Barraud, and K. Hurley on behalf 
of the HETE FREGATE Team;

report:

At 05:35:43.25 UTC (20143.25 s UT) on 26 October 2003, the HETE 
FREGATE and WXM instruments detected event H2882, a faint, long-hard 
GRB.

The burst triggered FREGATE in the 25-400 keV energy band.  Ground 
analysis of the WXM data provided a localization that was reported in 
a GCN Notice at 08:51:20 UT, 3.26 hours after the burst. The  WXM 
ground localization SNR was 6. The WXM localization can be expressed 
as a 90% confidence circle, with a radius of 15 arcminutes, centered 
at:

WXM-Ground:  R.A. = +03h 18m 42s, Dec. = +28d 21' 58" (J2000).

An automated fit of a cutoff power-law spectrum has been performed 
for H2882.  The fit of the model to the data is posted at

http://space.mit.edu/HETE/Bursts/GRB031026

 From the automated fit, the calculated values of Epeak and the burst 
fluence (25-100 keV) posted at the above website are:
--Epeak    	= 330 keV
--Fluence  	= 2.3e-06 erg/cm^2
--Duration(t90) 	= 114.2 seconds

Also posted at the above website are the following data, in the 
formats described by Vanderspek (GCN 2421
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 ):
--Fregate light curve and ascii data tables (energy bands A[7-30 
keV], B[7-80 keV], and C[30-400 keV])
--Color-color plot location of H2882 relative to other HETE-localized bursts
--Signal-to-noise histogram location of H2882 in Fregate Band C 
relative to other HETE-localized bursts

We note that the counts ratio (Band_B/Band_A > 1.8) for H2882 is one 
of the most extreme values yet measured by HETE.

This message may be cited.

GRB 031026 (=H2882): Evidence for High Redshift from Prompt Emission

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

C. Barraud, M. Boer, J-F Olive, and J-P Dezalay, on behalf of the 
HETE FREGATE Team;

T. Donaghy, C. Graziani, E. Fenimore, M. Galassi, M. Matsuoka, T. 
Sakamoto, Y. Shirasaki, M. Suzuki, T. Tamagawa, K. Torii, A. Yoshida, 
Y. Nakagawa, R. Satoh, Y. Urata, T. Yamazaki and Y. Yamamoto, on 
behalf of the HETE WXM Team;

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

report:

Careful spectral analysis of the prompt X-ray and gamma-ray emission 
of GRB 031026 (Butler et al; GCN 2429
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 ) confirms that this burst has a 
very hard spectrum.  This is unusual for relatively faint, long GRBs 
like GRB 030126.

We have computed a "pseudo-redshift" for GRB 031026, based on the 
spectral properties of its prompt high energy emission, using the 
prescription of Atteia (2003) (see A&A, 407, L1, for the definition 
of pseudo-redshift, or pseudo-z).  We determine a value of 14 for the 
pseudo-z.  This value is the highest one amongst the 40 HETE GRBs for 
which pseudo-z's have been calculated; only 3 of the 40 have 
pseudo-z's greater than 4:

GRB 020305, pseudo-z = 5.9
GRB 010612, pseudo-z = 9.5
GRB 031026, pseudo-z = 14.

For the 10 HETE GRBs with spectroscopic redshifts for which 
calculation of a pseudo-z has been possible, the pseudo-z is always 
within a factor of two of the spectroscopic redshift.  However, this 
agreement reflects to some degree the fact that the prescription used 
to calculate the pseudo-z's was optimized for these 10 bursts, and it 
has not been possible as yet to predict the pseudo-z's of an 
independent set of GRBs.  Furthermore, the 10 HETE bursts included in 
this fit span the redshift range z = 0.2 to z= 3.5, and thus no 
calibration of the pseudo-z prescription has yet been possible for a 
redshift as large as the pseudo-z value we find for GRB 031026. 
Nevertheless, we believe that it is important to report the pseudo-z 
we find for GRB 031026, given the possible importance of this burst.

Considering the unusually hard spectrum yet small peak flux of GRB 
031026, potentially revealing a source at very high redshift, we urge 
observers to perform deep observations of the HETE localization error 
circle for this burst (see GCN 2429
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  for more details) at other than 
optical wavelengths.  If the source of this burst truly lies at a 
very high redshift (z > 7), its optical afterglow could be 
undetectable as a result of absorption by the Lyman alpha forest, yet 
X-ray and/or IR observations might reveal a counterpart. Furthermore, 
at a fixed time of observation after the GRB, the effect of 
cosmological time dilation for a very high redshift could in 
principle increase the spectral flux in a given frequency band to 
such a degree that the afterglow would appear dramatically brighter 
than might otherwise be anticipated. Thus, a z=7 afterglow observed 
at 8 days after the burst could be as bright (e.g. in a fixed X-ray 
or IR band) as would a z=1 afterglow observed at 1 day after the 
burst (Lamb and Reichart 2000; Ciardi and Loeb 2000).

This result may be cited.

M. C. Nysewander, J. A. Moran, C. Zdanowicz, D. Reichart (U. North
Carolina) and M. Schwartz (Tenagra Observatories) report on behalf of the
FUN GRB Collaboration:

We twice observed the error circle of GRB 031026 (Bulter et al., GCN 2429
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 )
with the 32-inch Tenagra II telescope beginning 3.9 hours (Nysewander et
al., GCN 2428
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 ) and 25.7 hours after the burst.  We covered 99% of the error
circle in four pointings with a total integration time per pointing of 1350
sec for the first epoch and 1500 sec for the second epoch.

Using the image subtraction routine ISIS2 (Alard 2000), we find no
transients to the limiting magnitude of our first epoch image, which we
measure to be Ic = 20.4 mag (3 sigma) using five USNO-B1 stars for
calibration.

Assuming R_V = 3.1, the Galactic extinction along the line of sight is A_Ic
= 1.5 mag.

GCN Circular
Title: Lulin optical follow-up observations of GRB031026

A.C. Chen, H.C. Ting, H.C. Lin, K.Y. Huang, D. Kinoshita,W.H. Ip(NCU)
Y. Urata and T. Tamagawa (RIKEN) report:

"We have observed the entire region of HETE-2 error circle of
GRB031026 (N. Butler et al. GCN2429
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 ) with 1.0-m telescope Lulin
observatory (Institute of Astronomy, National Central University,
Taiwan) at 26.48-26.72 Oct 2003, corresponding 6-12 hours after the
burst.  We have imaged 9 fields by CCD camera (10'x10' field of view).
These average limiting magnitudes is about 20.9 (SN=3, compared with
USNO-A2.0 red magnitudes).  Comparing with Digitized Sky Survey (DSS2)
image, there are no new object down to the limiting magnitude."

The observation is summarized as follows:
 ---------------------------------------------------------------------
  Field  RA          DEC       Start    filter  Exp.(sec) Limit mag.
                              time(UT)
   1    03:17:55.5  +28:31:40 11:33       R      300 x 3   21.2
   2    03:17:56.8  +28:21:41 11:57       R      300 x 3   20.5
   3    03:17:58.1  +28:11:42 12:23       R      300 x 3   20.0
   4    03:19:27.2  +28:22:14 12:42       R      300 x 3   20.3
   5    03:19:26.0  +28:32:13 13:01       R      300 x 3   21.1
   6    03:19:28.4  +28:12:15 13:20       R      300 x 3   21.2
   7    03:18:42.0  +28:21:58 17:02       R      300 x 1   21.3
   8    03:18:40.8  +28:31:57 17:09       R      300 x 1   20.9
   9    03:18:43.2  +28:11:59 17:18       R      300 x 1   21.5
 ---------------------------------------------------------------------

This message may be cited.

F. Bertoldi (MPIfR Bonn), D.A. Frail (NRAO), E. Berger (Caltech),
K.M. Menten (MPIfR Bonn), S. Kulkarni (Caltech) report:

We have imaged a ca. 13 arcmin radius field around the WXM localization of
GRB031026 (Butler et al. GCN 2429
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 ), using the Max-Planck Millimeter
Bolometer array at the IRAM 30m telescope. We do not find any source
with a 250 GHz (1.2 mm) flux density >16 mJy (4 sigma upper limit)
within 10 armin of this position. The observations were conducted
between UT Oct 10.9 and Nov 2.2. Further details and maps can be found
at http://www.mpifr-bonn.mpg.de/staff/bertoldi/projects/grb031026

We wish to thank the IRAM staff for their flexibile scheduling of the
telescope, which made these observations possible.

This result may be cited.