Transient Science with the LEAP Polarimeter on ISS

The LargE Area burst Polarimeter (LEAP) will investigate the nature of gamma-ray burst jets by making via the first high-fidelity polarization and spectroscopy measurements of the prompt gamma-ray emission from a large sample of gamma-ray bursts (GRBs). LEAP is a proposed International Space Station (ISS) payload with a three-year mission designed to answer the following science questions. Are the jet magnetic fields randomly oriented or are their directions ordered? Are the jets dominated by matter or magnetic fields? Is the energy dissipated within the jet by internal shocks or by magnetic reconnection? Is the non-thermal emission mechanism synchrotron radiation, and what portion of the signal is of thermal photospheric origin? LEAP’s baseline mission requires observation of at least 65 GRBs with a sensitivity defined by a minimum detectable polarization (MDP) of 30%. The current LEAP design is expected to trigger on approximately 400 GRBs, with about 86 of those having an MDP <30%. LEAP will enable rapid community follow-up to better understand GRBs and their environments.

The LEAP design enables a broad range of secondary science while achieving its baseline mission. During overlap between LIGO’s A+ configuration, approximately 3 joint GW/GRB detections per year are expected with LEAP. LEAP will also be sensitive to magnetar bursts, which have recently been associated with Fast Radio Bursts and will potentially measure polarization for bright individual bursts or stacked collections of bursts. LEAP will extend pulse flux and spin frequency histories for accreting pulsars with a sensitivity similar to Fermi GBM, and will potentially measure polarization for their brightest outbursts. The LEAP mission is scheduled during the declining phase of Solar Cycle 25, during which many intense flares are likely to occur; LEAP will make the most sensitive measurements to date of solar flare polarization. LEAP will open a new window into the nature of the most energetic phenomena in the universe with gamma-ray polarization.