The Gamma-Ray Polarimeter Experiment (GRAPE) is a high-altitude balloon experiment designed for polarization studies of transient sources with a long-term goal of observing Gamma-Ray Bursts (GRBs) aboard a series of Long Duration Balloon flights (LDBs). Polarization studies of GRB prompt emission is necessary to constrain existing physics models describing the radiation processes and magnetic field structures of astrophysical jets. GRAPE is a wide field of view (FoV) Compton polarimeter measuring γ-ray polarization in the 50-500 keV energy range with a broad range (20 keV – 3 MeV) for spectroscopy. The novel 3-dimensional geometry of the current design provides GRAPE with Compton imaging in addition to polarization capabilities. The instrument consists of 245 optically isolated SiPM coupled to either high-Z (GAGG:Ce) or low-Z (para-Terphenyl) scintillator arranged in a 7x7x5 cuboid structure. At the center of the scintillator array two low-Z detectors contain a ~25 nCi Co-60 calibration source for onboard calibrations. A test flight of this design was flown on August 27, 2023, from Fort Sumner, NM to validate the scientific capability of the instrument design. We will report on res
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 Gamma-Ray Polarimeter (GRAPE) is a wide field of view (FoV) Compton polarimeter measuring γ-ray polarization from transient sources such as Gamma-Ray Bursts (GRBs) in the 50-500 keV energy range with a broad range (20 keV – 3 MeV) for spectroscopy. The instrument is a 7x7x5 array of 245 optically isolated SiPMs each coupled to either a high-Z (GAGG:Ce) or low-Z (para-Terphenyl) scintillator. The novel design provides enables Compton imaging in addition to polarization capabilities, and Co-60 calibration sources (~25 nCi) imbedded within two centrally located low-Z detectors allow for onboard calibrations. We will report on the instrument performance of this design during a test flight on August 27, 2023, from Fort Sumner, NM.
Understanding the underlying physics governing astrophysical jets associated with Gamma-Ray Bursts (GRBs) is necessary to advance the field of gamma-ray astronomy. Existing physics models can be constrained through GRB polarization studies. The Gamma-Ray Polarimeter Experiment (GRAPE) is a high-altitude balloon experiment designed to measure GRB polarization over the energy range of 50-500 keV at flight altitudes. A flight of the newest GRAPE design is scheduled to fly from Fort Sumner, NM in August 2023. The new design is based on an arrangement of small scintillation detector elements designed to measure photon interactions in three dimensions and provide modest imaging capabilities. The flight instrument consists of a 3-dimensional (7x7x5) array of high-Z (GAGG) and low-Z (P-terphenyl) scintillators each read out by individual Hamamtsu MultiPixel Photon Counters (MPPCs). Previous GRAPE missions have been sensitive to M-class solar flares and observations of the Crab Nebula with low signal to background ratios. The new design improves performance relative to the previous GRAPE design through the use of advanced scintillator materials, the ability to perform modest Compton imaging for source localization and background rejection, and by completely eliminating optical cross-talk. Background reduction is achieved using the imaging capabilities allowing for some level of event rejection for events inconsistent with the source direction. This paper will present the new module design and simulated response parameters to provide an estimate of the balloon payload sensitivity.
The gamma-ray polarimeter experiment (GRAPE) is a NASA-funded high-altitude scientific balloon experiment. For over a decade, GRAPE has been developing wide field of view (FoV) scintillator-based Compton polarimeters designed to measure gamma-ray polarization from GRBs over the energy range of 50-500 keV. A variant of a GRAPE design was tested in flight in 2011 and 2014. A new design is scheduled to fly in Fort Sumner, New Mexico in August of 2023. The new design of GRAPE incorporates an assemblage of 245 optically isolated high-Z and low-Z scintillators each read out by individual silicon photomultipliers (SiPMs) and arranged in a 3-dimensional 7x7x5 cuboid layout which provides moderate imaging capabilities. The cube design of GRAPE is expected to improve performance with respect to previous GRAPE missions by eliminating optical cross-talk and using the instrument’s imaging capability to reduce instrument background. To standardize the development process for the flight instrument, select optimal technology to optimize the design features, and build a framework for the analysis and simulation of the 245 detector instrument, a small-scale prototype instrument of the cube design was developed and studied in the lab using simulations and lab measurements of unpolarized sources. The results of these studies are presented here along with an overview of the 7x7x5 flight instrument and mission.
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