Cadmium-Zinc-Telluride Imager (CZTI) is one of the five payloads on-board recently launched Indian astronomy satellite AstroSat. CZTI is primarily designed for simultaneous hard X-ray imaging and spectroscopy of celestial X-ray sources. It employs the technique of coded mask imaging for measuring spectra in the energy range of 20 - 150 keV. It was the first scientific payload of AstroSat to be switched on after one week of the launch and was made operational during the subsequent week. Here we present preliminary results from the performance verification phase observations and discuss the in-orbit performance of CZTI.
Importance of polarisation measurement of X-rays from celestial sources has been realized for long time. Such
measurements can provide unique opportunity to study the behaviour of matter and radiation under extreme
magnetic and gravitational fields. However sensitivity of the X-ray polarimeters has always been an issue and as a
result no X-ray polarization measurement has been flown in last three decades. The situation is expected to change
in near future with launch of GEMS, but these polarisation measurements will be limited to energies below 10KeV.
On the other hand most of the X-ray sources are expected to have higher degree of polarisation at higher energies.
With the advent of high energy focussing telescopes (e.g. NuSTAR, ASTRO-H), it is now possible to design a focal
plane Compton polarimeter which can be sensitive upto 80KeV. However, X-ray polarisation measurement is
extremely photon hungry. Therefore, a dedicated X-ray polarimeter always has lower sensitivity when compared to
any other type of X-ray detector for equal collecting area and time. In this context, we explore a new design of hard
X-ray focal plane detector which can provide simultaneous measurements of X-ray polarisation measurements along
with high resolution X-ray spectroscopy as well as timing. This design employs a sandwich of a 0.5mm thick Si
detector and 10mm thick plastic detector which is surrounded by a cylindrical array of scintillator detectors. Here we
present results of detailed Geant4 simulations for estimating sensitivity of this configuration.