There is a growing interest in the science uniquely enabled by observations in the MeV range, particularly in light of multi-messenger astrophysics. The Compton Pair (ComPair) telescope, a prototype of the AMEGO Probe-class concept, consists of four subsystems that together detect and characterize gamma rays in the MeV regime. A double-sided strip silicon Tracker gives a precise measure of the first Compton scatter interaction and tracks pair-conversion products. A novel cadmium zinc telluride (CZT) detector with excellent position and energy resolution beneath the Tracker detects the Compton-scattered photons. A thick cesium iodide (CsI) calorimeter contains the high-energy Compton and pair events. The instrument is surrounded by a plastic anti-coincidence (ACD) detector to veto the cosmic-ray background. In this work, we will give an overview of the science motivation and a description of the prototype development and performance.
The Gamma RAy Polarimeter Experiment (GRAPE) was first own on a 26-hour balloon flight in the fall of 2011. GRAPE consists of an array of Compton polarimeter modules (based on traditional scintillation technologies) designed to operate in the energy range from 50 keV up to 500 keV. The ultimate goal of our program is to operate GRAPE in a wide FoV configuration for the study of gamma-ray bursts. For the first balloon flight, GRAPE was configured in a collimated mode to facilitate observations of known point sources. The Crab nebula/pulsar, the active Sun, and Cygnus X{1 were the primary targets for the first flight. Polarization results from this flight are summarized. Plans for the next GRAPE balloon flight, which is scheduled to take place in the fall of 2014 from Ft. Sumner, NM, will also be presented. These plans involve modifications designed to improve the polarization sensitivity, including an expansion of the array of polarimeter modules from 16 to 24 and improvements to the instrument shielding. These improvements to the instrument will significantly improve the polarization sensitivity, enabling a measurement of the Crab Nebula polarization to be made during the 2014 balloon flight.
The Gamma RAy Polarimeter Experiment (GRAPE) was first flown on a 26-hour balloon flight in the fall of 2011.
GRAPE consists of an array of Compton polarimeter modules (based on traditional scintillation technologies) designed
to operate in the energy range from 50 keV up to 500 keV. The ultimate goal is to operate GRAPE in a wide FoV
configuration for the study of gamma-ray bursts. For the first (demonstration) balloon flight, GRAPE was configured in
a collimated mode to facilitate observations of known point sources. The Crab nebula/pulsar, the active Sun, and Cygnus
X-1 were the primary targets for the first flight. Although the Crab was detected, the polarization sensitivity was worse
than expected. This paper will review the plans for the next GRAPE balloon flight, which is scheduled to take place in
the fall of 2014 from Ft. Sumner, NM. These plans involve several modifications designed to improve the polarization
sensitivity, including an expansion of the array of polarimeter modules from 16 to 24 and improvements to the
instrument shielding. Sensitivity estimates of the resulting instrument, based on GEANT4 simulations, will be presented.
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