The LargE Area burst Polarimeter (LEAP) A NASA Mission of Opportunity for the ISS

The LargE Area Burst Polarimeter (LEAP) will radically improve our understanding of some of the most energetic phenomena in our Universe by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects. LEAP will do this by making the highest fidelity polarization measurements to date of the prompt gamma-ray emission from a large sample of Gamma-Ray Bursts (GRBs). The LEAP science objectives are met with a single instrument - a wide FOV Compton polarimeter that measures GRB polarization over the energy range from 50-500 keV and performs GRB spectroscopy from 20 keV to 5 MeV. It will be deployed as an external payload on the International Space Station (ISS) in 2025 for a three year mission. The instrument is based on standard, well-proven technologies that requires no new technology development. LEAP measures polarization using seven independent polarimeter modules, each with a 12x12 array of optically isolated high-Z and low-Z scintillation detectors read out by individual PMTs. The large FOV derives from the random distribution of GRBs in both space and time, and means that there is no preferred pointing direction on the celestial sphere. This feature, combined with the resources, and well-understood operations of ISS, provide the foundation for a straightforward mission design. LEAP is one of two NASA Missions of Opportunity proposals that are currently in a Phase A Concept Study, with a final selection due later this year.