TITLE: GCN CIRCULAR NUMBER: 8632 SUBJECT: GRB081203A: Ashra-1 observation of early optical and VHE-neutrino emission DATE: 08/12/07 16:54:46 GMT FROM: Makoto Sasaki at ICRR/U.Tokyo 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. 8595) 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 ////////////////////////////////////////////////////////////////