Hard X-ray and Soft Gamma Ray Polarimetry with CdTe/CZT Spectro-Imager

Abstract

CdTe/CZT based spectroscopic two-dimensional (2D)/three-dimensional (3D) imagers when operated in the Compton regime can work as high performance scattering polarimeters, for high-energy astrophysics. Polarimetry in high-energy astrophysics has been little explored. To date, X-and γ-ray source emissions have been studied almost exclusively through spectral, imaging, and timing analysis. Polarization measurements provide two additional observational parameters: the polarization angle and the level of linear polarization. These additional parameters should allow for a better discrimination between the physical mechanisms of different emission models characterizing a celestial object. Therefore, polarimetry will play a strategic role in new instrumentations for future high-energy astronomy missions. 2D and 3D CZT/CdTe spectroscopic imagers provided with coincidence readout logic can efficiently handle scattering events to perform simultaneously polarization, spectroscopy, imaging, and timing measurements. Herein, we describe the results obtained, both experimentally and by MC simulations, with CdTe/CZT pixel detector prototypes in high-energy polarimetry. We give an overview on the achievable polarimetric performance with spectroscopic imagers and on how these performances are affected by detector configuration parameters. Finally, we address the perspective of scattering polarimetry opened by the recent implementation of new high energy focusing optics, as broadband Laue lens, in next generation of hard X-and soft γ-ray astronomy instrumentation. The unprecedented sensitivity achievable by these telescopes will definitely open the window of polarimetry in this high-energy range.

Understanding the origin of the positron annihilation line and the physics of supernova explosions

“…The measured three-dimensional position resolution of a single element matches that required by the ASTENA NFT: 300 μm [50,51]. In this configuration, the PSD is also capable to work as a Compton polarimeter [16].…”

“…Fig 16. Minimum Detectable Polarization (MDP) in 10 5 s as a function of the polarized source intensity (red line) and for a 10 mCrab source as a function of the observation time (blue line).…”

Hard X-ray Polarimetry -- An overview of the method, science drivers and recent findings

“…Consistent with this discussion, we have seen a lot of efforts in the last few years to develop Rayleigh polarimeters in 10 − 30 keV range (Paul et al, 2016) and Compton polarimeters at higher energies both as focal plane detector (Chattopadhyay et al, 2013(Chattopadhyay et al, , 2014aChattopadhyay et al, 2015;Krawczynski et al, 2011) and large area of scintillators or CZTs or Germanium detectors (McConnell et al, 2009;Chattopadhyay et al, 2014b;Vadawale et al, 2015;Orsi & Polar Collaboration, 2011;Caroli et al, 2012Caroli et al, , 2018Yang et al, 2018). In the next section, we will review instrumentation of different scattering polarimetry configurations suitable in the three energy bands: 10 − 25 keV, 25 − 80 keV and beyond 80 keV.…”

“…Multiple groups across the globe are actively involved in developing CZT detectors optimized for polarimetry and experimentally demonstrating their polarization measurement capability (see an overview on the ongoing efforts by Caroli et al, 2018). CZT Imager (CZTI, Bhalerao et al, 2017;Rao et al, 2016) on board AstroSat (Agrawal, 2006;Singh et al, 2014) is a large area coded mask hard X-ray spectrometer.…”

“…Compton polarimetry based on 3D CZT detectors has already been evaluated and proposed (Caroli et al, 2012). See Caroli et al (2018) for an overview of 3D CZT detector development for polarimetry experiments. The uncertainty in determining the Compton scattering angle depends on the energy resolution of the detector for E 1 (1 st interaction) and E 2 (2 nd interaction) and E, total energy (see Eq.…”