GRAINE project, prospects for scientific balloon-borne experiments

Abstract

We are pushing forward with the GRAINE project, a 10-MeV to 100-GeV cosmic γ-ray observation project that uses an emulsion telescope with high angular resolution (0.08° at 1–2GeV) and polarization sensitivity, and a large aperture area (∼10m2), by repeating long-duration balloon flights. Through various ground experiments, a balloon-borne experiment in 2011, and a balloon-borne experiment in 2015, the feasibility of cosmic γ-ray observations with a balloon-borne emulsion telescope was pioneered. Through scientific balloon-borne experiments, we can attempt to achieve the following: pioneering polarization observations for high-energy γ rays from pulsars, active galactic nuclei, flares, and γ-ray bursts; direct probing of proton acceleration by π0 feature detection and approaching an emission mechanism with a spatial structure for supernova remnants; resolving GeV γ-ray excess at the galactic center region; probing new physics beyond the Planck scale by polarization observations with high-energy γ rays propagating over cosmological distances; observing transient sources, e.g. γ-ray bursts and flares, with a high sensitivity, high photon statistics and polarization sensitivity. Developments in scientific balloon-borne experiments are ongoing.