Instrument aboard Japan’s IKAROS spacecraft, which is the first polarimeter specifically designed to measure the polarization of intense flashes of gamma rays from space known as gamma-ray bursts. GAP is a modest detector (3.8 kg in weight and 17 cm in size) with an energy range of 50–300 keV. Using this instrument, a team of Japanese scientists have made the most precise measurements of energetic gamma-ray burst photons to date.