OBSERVATIONAL SEARCH FOR PeV-EeV TAU NEUTRINO FROM GRB081203A

We report the first observational search for tau neutrinos (ντ) from gamma-ray bursts (GRBs) using one of the Ashra light collectors. The Earth-skimming ντ technique of imaging Cherenkov τ showers was applied as a detection method. We set stringent upper limits on the ντ fluence in PeV-EeV region for 3780 s (between 2.83 and 1.78 hr before) and another 3780 s (between 21.2 and 22.2 hr after) surrounding GRB081203A triggered by the Swift satellite. This first search for PeV-EeV ντ complements other experiments in energy range and methodology, and suggests the prologue of 'multi-particle astronomy' with a precise determination of time and location.