One of the least explored aspect of gamma-ray burst (GRB) prompt emission is its polarization. Polarization measurements add a new dimension to the study of GRBs. It reveals the strength, coherence length and topology of the magnetic fields and the geometry of the relativistic outflow. Existing polarization data have limited sensitivity and show conflicting results. LEAP with its large effective area will provide high sensitivity polarization measurements required to understand GRB jets and their geometry. LEAP is proposed as an International Space Station external payload, launching in 2025, and was selected by NASA for a Phase A concept study. In addition to GRBs, LEAP will enable a wide range of secondary science such as searching for gravitational wave counterparts, polarization sensitive observations of Solar flares, terrestrial gamma-ray flashes or soft gamma-repeaters.
Here we show how LEAP will constrain models of gamma-ray bursts. One of the leading emission mechanisms is synchrotron radiation which typically involves high degrees of polarization. Based on the GRB prompt emission properties measured by Fermi-GBM and gamma-ray emission models, we will show polarization estimates tailored to the sensitivity of LEAP. We will update and expand the models compiled in Toma et al. 2009, that consider different magnetic field topologies (ordered or random) and emission mechanisms (Compton scattering or synchrotron). Using simulations, we investigate the role of the Lorentz factor distribution in shaping the expected polarization measurements. We expand models to include jets with angular structure and use improved jet opening angle distribution.