Galactic Bulge Monitor with Ashra-1 and NTA detectors

Abstract

The Ashra phase-1 (Ashra-1) detector has been developed to efficiently take fine images of air-shower (AS) Cherenkov (CE) and fluorescence (FL) light induced by the Earth-skimming ντ and γ-ray ASs. Based on the Ashra-1 performance, we have planned a new extension, i.e. Neutrino Telescope Array (NTA), an AS imaging ν and γ-ray observation system for Clear Discovery and Identification of Non-thermal Hadronic Processes in the Universe. Four NTA stations are to be deployed on Mauna Loa at 3000-3500 m a.s.l. (NTA Summit Array layout). Using the four stations, NTA can watch the air volume surrounding Mauna Loa including the surface of Mauna Loa, the largest volcano, Hawaii Island and sea around it to efficiently detect CE and FL light from ντ ASs with both short and long decay lengths and γ-ray ASs. From the detailed MC studies, the NTA ντ sensitivity is sufficient to probe Pevatorons, an extension of the IceCube detected astrophysical neutrino flux and predictions of the cosmogenic neutrino flux. The point-back accuracy is evaluated to be within 0.2 degrees with respect to the original direction of the PeV-scale ES ντ ’s. As the first step observation with the minimal systematic deployment, we propose to monitor 10 TeV-10PeV γ-rays from the Galactic bulge with Ashra-1 as well as Earth-skimming ντ ’s with NTA simultaneously to clearly identify the Pevatrons and comprehensively understand the emission process there. The effective detection area of Ashra-1 and NTA for the Galactic bulge γ-rays with the energies around 1 PeV is more than 10 and 100 times respectively larger than that of a ground array with 500m scale.