Since the initial exploration of soft gamma-ray sky in the 60's, high-energy
celestial sources have been mainly characterized through imaging, spectroscopy
and timing analysis. Despite tremendous progress in the field, the radiation
mechanisms at work in sources such as neutrons stars and black holes are still
unclear. The polarization state of the radiation is an observational parameter
which brings key additional information about the physical process. This is why
most of the projects for the next generation of space missions covering the
tens of keV to the MeV region require a polarization measurement capability. A
key element enabling this capability is a detector system allowing the
identification and characterization of Compton interactions as they are the
main process at play. The hard X-ray imaging spectrometer module, developed in
CEA with the generic name of Caliste module, is such a detector. In this paper,
we present experimental results for two types of Caliste-256 modules, one based
on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed
to linearly polarized beams at the European Synchrotron Radiation Facility.
These results, obtained at 200-300 keV, demonstrate their capability to give an
accurate determination of the polarization parameters (polarization angle and
fraction) of the incoming beam. Applying a selection to our data set,
equivalent to select 90 degrees Compton scattered interactions in the detector
plane, we find a modulation factor Q of 0.78. The polarization angle and
fraction are derived with accuracies of approximately 1 degree and 5%. The
modulation factor remains larger than 0.4 when essentially no selection is made
at all on the data. These results prove that the Caliste-256 modules have
performances allowing them to be excellent candidates as detectors with
polarimetric capabilities, in particular for future space missions.Comment: 17 pages, 14 figures, 2 tables in Experimental Astronomy, 201
