Polarization measurements in the X-ray and gamma-ray energy range can provide crucial information on massive compact objects such as black holes and neutron stars .
The Polarized Gamma-ray Observer ( PoGO ) is a new balloon-borne instrument designed to measure polarization from astrophysical objects in the 30-100 keV range , under development by an international collaboration with members from United States , Japan , Sweden and France .
To examine PoGO ’ s capability , a beam test of a simplified prototype detector array was conducted at the Argonne National Laboratory Advanced Photon Source .
The detector array consisted of seven plastic scintillators , and was irradiated by polarized photon beams at 60 , 73 , and 83 keV .
The data showed a clear polarization signal , with a measured modulation factor of 0.42 \pm 0.01 .
This was successfully reproduced at the 10 % level by the computer simulation package Geant4 after modifications to its implementation of polarized Compton/Rayleigh scattering .
Details of the beam test and the validation of the Geant4 simulations are presented .