Compton polarimetry with a multi-layer CdTe focal plane prototype

Abstract

In high-energy astrophysics, polarimetry is a promising subject with a wide scientific potential that is relatively unexplored due to the complexity of the design and technical requirements of the sensors. Often gamma-ray telescope proposals are based on multi-layer spectro-imager instruments with polarimetric capabilities. Herein we study a new Compton polarimeter prototype based on a two-layer CdTe pixelized spectro-imager operated in coincidence. The two CdTe detectors are 2 mm thick anode 8 ×8 pixels' segmented matrices with 2 mm pitch. This detection system configuration allows an assessment of the polarimetric potential of multi-layer solution focal planes as well as the polarimetric potential of a possible 3D spectro-imager by analysing the polarimetric performance when varying the distance between the two CdTe detection layers. The polarimetric modulation factors for single-layer (Q ∼0.4) and two-layer (up to 0.13) double-events were measured for 6 mm and for 10 mm distance between planes. The measured polarization angle resolution was lower than 10°. The potential of CdTe spectro-imager focal plane solutions with polarimetric capabilities for the next generation space missions based on both Laue lenses and 3D segmented focal planes is also discussed.