Abstract
Observation of cosmic gamma rays is important in the understanding of high-energy objects or phenomena in the universe. Since 2008, the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope (Fermi-LAT) has surveyed the sub-GeV/GeV gamma-ray sky and achieved high statistics measurements. However, observation at low galactic latitudes remains difficult owing to the lack of angular resolution, and new issues following the operation of Fermi-LAT have arisen. We devised a precise gamma-ray observation project, Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE), using balloon-borne emulsion gammaray telescopes to realize high angular resolution, polarization-sensitive, and large-aperture observations in the 10 MeV–100 GeV energy region. Following basic developments on the ground, we performed three balloon-borne experiments with upgraded instruments. In this paper, we present results from the second balloon experiment in 2015, a report on the latest balloon experiment conducted on April 26, 2018, and a recent study on hadronic interactions using proton beams.
Highlights
Gamma rays are one of the most important probes to explore the high-energy phenomena in the universe
The Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE) is a precise observation project of cosmic gamma-rays in the 0.1–100 GeV energy region, using a balloon-borne large-aperture telescope based on nuclear
We present the current status of the GRAINE project
Summary
Gamma rays are one of the most important probes to explore the high-energy phenomena in the universe. The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope (Fermi-LAT) [1], which is the latest subGeV/GeV gamma-ray detector, has surveyed the entire gamma-ray sky and provided cosmic gamma-ray data with high statistics since its launch in 2008. The Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE) is a precise observation project of cosmic gamma-rays in the 0.1–100 GeV energy region, using a balloon-borne large-aperture telescope based on nuclear. We have developed various detector components using accelerator beam tests (gamma rays at SPring, muons at Muon Pit of the neutrino beam line in JPARC, electrons at linear accelerator, and protons at the Super Proton Synchrotron (SPS) at CERN) [10,11,12,13,14], observations at ground and mountain levels (Norikura) [11, 15], and three balloon-borne experiments.
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