  The Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat consists of an
array of a large number of pixellated CZT detectors capable of measuring the
polarization of incident hard X-rays. The polarization measurement capability
of CZTI for on-axis sources was experimentally confirmed before the launch.
CZTI has yielded tantalizing results on the X-ray polarization of the Crab
nebula and pulsar in the energy range of 100 - 380 keV. CZTI has also
contributed to the measurement of prompt emission polarization for several
Gamma-Ray Bursts (GRBs). However, polarization measurements of off-axis sources
like GRBs are challenging. It is vital to experimentally calibrate the CZTI
sensitivity to off-axis sources to enhance the credence of the measurements. In
this context, we report the verification of the off-axis polarimetric
capability of pixellated CZT detectors through the controlled experiments
carried out with a CZT detector similar to that used in CZTI and extensive
Geant4 simulations of the experimental set-up. Our current results show that
the CZT detectors can be used to measure the polarization of bright GRBs up to
off-axis angles of ~60 degrees. However, at incidence angles between 45-60
degrees, there might be some systematic effects which needs to be taken into
account while interpreting the measured polarisation fraction.

Instrumentation and Methods for Astrophysics;High Energy Astrophysical Phenomena