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GCN Circular 8632

Subject
GRB081203A: Ashra-1 observation of early optical and VHE-neutrino emission
Date
2008-12-07T16:54:46Z (16 years ago)
From
Makoto Sasaki at ICRR/U.Tokyo <sasakim@icrr.u-tokyo.ac.jp>
Y.Aita, Y.Asaoka, T.Chonan, Y.Higashi, K.Noda, and M.Sasaki
(ICRR,Univ.Tokyo), Y.Morimoto, S.Ogawa (Toho Univ.), J.Learned
(Univ.Hawaii Manoa), R.Fox (Univ.Hawaii Hilo) report on behalf of the
Ashra-1 collaboration:

We have searched for optical and VHE-neutrino emission in the field of
GRB081203A (A. M. Persons et al., GCN Circ. 8595Loading...
 
 ) around the
BAT-triggered GRB time (T0) with one of the light collector units in
the Ashra-1 detector (http://www.icrr.u-tokyo.ac.jp/~ashra) on Mauna
Loa on Hawaii Island (latitude = 19.5412 deg. N, longitude =155.5676
deg. W, altitude =3330m).

The Ashra-1 light collector unit has the achieved resolution of a few
arcmin, viewing 42 degree circle region of which center is located at
Alt = 11.7 deg, Azi = 22.1 deg. The sensitive region of wavelength is
similar with the B-band.

We quickly analyzed 83 images covering the field of GRB081203A every
7.2s with 6s exposure time respectively during the observation between
T0-300s and T0+300s. We detected no new optical object within the PSF
resolution around the GRB081203A determined by Swift-UVOT (M. De
Pasquale et al.,GCN Circ. 8603).

As a result of our preliminary analysis, the following 3-sigma
limiting magnitudes are derived:
----------------------------------------------------------------------
Starting&Ending Exp.Time,  3-sigma Limit. Mag.
----------------------------------------------------------------------
-297.7   -291.7                    11.9
-290.7   -284.7                    11.9
   .        .                       .
   .        .                       .
 -1.7      4.3                    11.9
  5.3     11.3                    11.8
   .        .                       .
   .        .                       .
 287.3    293.3                    11.9
 294.3    300.3                    11.9
----------------------------------------------------------------------
The limiting magnitudes were estimated in comparison with stars in
Tycho-2 Catalog to be distributed between 11.7 and 12.0 as above
partly listed.

Adding that we have searched for VHE-neutrino emission with the
primary neutrino energy above 10^16eV by detecting Cherenkov lights
from tau-decay induced air-showers. VHE neutrinos are expected to be
produced at the GRB behind Mauna Kea and converted into tau leptons in
the mountain rock. The GRB position was passed through our triggering
region viewing onto the face of Mauna Kea from 11:07UT to 11:49UT
(2.83 hours to 2.13 hours before the GRB). We have no signal come out
of the mountain. The limiting flux is now under analysis.

Figures of limiting optical magnitudes vs time comparing with other
measurements and more details on the VHE neutrino observation can be
found at: http://www.icrr.u-tokyo.ac.jp/~ashra/GRB081203A.

This message may be cited.

////////////////////////////////////////////////////////////////
SASAKI Makoto
ICRR, University of Tokyo
5-1-5 Kashiwa-no-ha Kashiwa 277-8582
tel/fax +81-4-7136-3143
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