  X-ray polarization measurement of cosmic sources provides two unique
parameters namely degree and angle of polarization which can probe the emission
mechanism and geometry at close vicinity of the compact objects. Specifically,
the hard X-ray polarimetry is more rewarding because the sources are expected
to be intrinsically highly polarized at higher energies. With the successful
implementation of Hard X-ray optics in NuSTAR, it is now feasible to conceive
Compton polarimeters as focal plane detectors. Such a configuration is likely
to provide sensitive polarization measurements in hard X-rays with a broad
energy band. We are developing a focal plane hard X-ray Compton polarimeter
consisting of a plastic scintillator as active scatterer surrounded by a
cylindrical array of CsI(Tl) scintillators. The scatterer is 5 mm diameter and
100 mm long plastic scintillator (BC404) viewed by normal PMT. The photons
scattered by the plastic scatterer are collected by a cylindrical array of 16
CsI(Tl) scintillators (5 mm x 5 mm x 150 mm) which are read by Si
Photomultiplier (SiPM). Use of the new generation SiPMs ensures the compactness
of the instrument which is essential for the design of focal plane detectors.
The expected sensitivity of such polarimetric configuration and complete
characterization of the plastic scatterer, specially at lower energies have
been discussed in Chattopadhyay et al. (Exp. Astron. 35, 391-412, 2013;
Astrophys. J. Suppl. 212, 12, 2014). In this paper, we characterize the CsI(Tl)
absorbers coupled to SiPM. We also present the experimental results from the
fully assembled configuration of the Compton polarimeter.
