The LargE Area burst Polarimeter (LEAP) is a proposed Compton scattering polarimeter that will, for the first time, measure the level of polarization for a significant number of GRBs with sufficient sensitivity to determine the magnetic field structure, composition, energy dissipation mechanism of GRB jets, and determine the prompt emission mechanism of GRBs. Once approved, LEAP will be deployed as an external payload on the International Space Station (ISS) where it will measure GRB polarization over the energy range from 50–1000 keV, perform GRB spectroscopy from 20 keV to 6 MeV, and self-sufficiently determine the source direction. LEAP is uniquely suited to fill a critical gap in our knowledge regarding GRBs, by exposing the underlying physics that governs astrophysical jets and the extreme environment surrounding newborn compact objects.
The study of gamma-ray burst (GRB) jets has focused predominantly on the gamma-ray portion of the spectral energy distribution (SED) to understand jet properties and their physics. Recent theoretical development has turned to the lower-energy side of the SED to test competing jet models. We considered the application of wide-field X-ray detectors to extend the observation of the SED and for better distinguishing spectral models, aimed at resolving theoretical features existing at or below the sensitivity of missions such as Fermi and Swift. A proposed SmallSat reference mission is introduced, and analysis is conducted on simulated GRBs to determine its improvement in understanding the SED compared with the Fermi-gamma-ray burst monitor (GBM). Detection rates of the reference mission are simulated using a GRB population model and convolved with the energy flux needed to resolve models to find estimated rates of GRBs that the reference mission can resolve better than Fermi-GBM. We discuss the methods and results along with the scientific context for this type of mission.
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 science objectives are met with a single instrument deployed as an external payload on the ISS – a wide FOV Compton polarimeter that measures GRB polarization from 50–500 keV and GRB spectra from ~10 keV to 5 MeV. LEAP measures polarization using seven independent polarimeter modules, each with a 12x12 array of optically isolated high-Z and low-Z scintillation detectors readout by individual PMTs. 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.
The LargE Area burst Polarimeter (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. It is a wide Field of View (FoV) Compton polarimeter designed to study Gamma-Ray Burst (GRB) polarization over the energy range from 50- 500 keV and to measure GRB spectra in the range from 20 keV - 5 MeV. During the Phase A Concept Study, lab measurements were conducted with a small-scale (5x5) prototype polarimeter module. This included both spectral and polarization measurements with laboratory calibration sources. Here the prototype measurements and the comparisons made with simulations of the prototype detector are described. These results demonstrate the basic functionality of the LEAP design.
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