Prospects of hard X-ray polarimetry with Astrosat-CZTI
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Astrosat is the first Indian satellite mission dedicated for astronomical studies. It is planned for launch during 2014 and will have five instruments for multi-wavelength observations from optical to hard X-rays. Cadmium Zing Telluride Imager (CZTI) is one of the five instruments aiming for simultaneous X-ray spectroscopy and imaging in the energy range of 10 keV to 100 keV (along with all sky photometric capability unto 250 keV). It is based on pixilated CZT detector array with total geometric area of 1024 cm2. It will have two-dimensional coded mask for medium resolution X-ray imaging. The CZT detector plane will be realized using CZT detector modules having integrated readout electronics. Each CZT detector module consists of 4 cm × 4 cm CZT with thickness of 5 mm which is further pixilated into 16 × 16 array of pixels. Thus each pixel has size of 2.5 mm × 2.5 mm and thickness of 5 mm. Such pixilated detector plane can in principle be used for hard X-ray polarization measurements based on the principle of Compton scattering by measuring azimuthal distribution of simultaneous events in two adjacent pixels. We have carried out detailed Geant4 simulations for estimating polarimetric capabilities of CZTI detector plane. The results indicate that events in the energy range of 100 keV to 250 keV, where the 5 mm thick CZT detector has significant detection efficiency, can be used for polarimetric studies. Our simulation results indicate the minimum detectable polarization (MDP) at the level of ∼ 10% can be achieved for bright Crab like X-ray sources with exposure time of ∼500 ks. We also carried out preliminary experiments to verify the results from our simulations. Here we present detailed method and results of our simulations as well as preliminary results from the experimental verification of polarimetric capabilities of CZT detector modules used in Astrosat CZTI.
KeywordsX-ray polarimetry Instrumentation Compton scattering Astrosat-CZT imager
Research at Physical Research Laboratory, Ahmedabad is supported by the Department of Space, Government of India. The authors thank the technical assistance provided by the CZT-Imager team at TIFR as well as at IUCAA.
- 9.Guo, Q., Beilicke, M., Garson, A., Kislat, F., Fleming, D., et al.: Optimization of the design of the hard X-ray polarimeter X-Calibur. Astropart. Phys. 41, 63–72 (2013) doi: 10.1016/j.astropartphys.2012.11.006
- 11.Heitler,W.: The Quantum Theory of Radiation, 3rd edn. Oxford University Press, Oxford (1954)Google Scholar
- 13.Jahoda, K.: The gravity and extreme magnetism small explorer. In: Proceedings SPIE Conference, vol. 7732 (2010)Google Scholar
- 21.Soffitta, P., Costa, E., Muleri, F., Campana, R., Del Monte, E., et al.: A set of x-ray polarimeters for the new hard X-ray imaging and polarimetric Mission. In: Proceedings SPIE Conference, vol. 7732, 2010.Google Scholar
- 23.Vadawale, S.V., Chattopadhyay, T., Pendharkar, J.: A conceptual design of hard X-ray focal plane detector for simultaneous x-ray polarimetric, spectroscopic, and timing measurements. In: Proceedings SPIE Conference, vol. 8443 (2012)Google Scholar
- 24.Vadawale, S.V., Hong, J.S., Masui, H., Grindlay, J.E., Williams, P., et al.: Multipixel characterization of imaging CZT detectors for hard x-ray imaging and spectroscopy. In: Proceedings SPIE Conference, vol. 5540 (2004)Google Scholar
- 25.Vadawale, S.V., Purohit, S., Shanmugam, M., Acharya, Y.B., Goswami, J.N., et al.: Characterization and selection of CZT detector modules for HEX experiment onboard Chandrayaan-1, Vol. 598, pp. 485–495 (2009)Google Scholar
- 26.Vadawale, S.V., Sreekumar, P., Acharya, Y.B., Shanmugam, M., Banerjee, D., et al.: Hard X-ray continuum from lunar surface: results from high energy X-ray spectrometer (HEX) onboard Chandrayaan-1. In: Advances in Space Resarch. Accepted for Publication (2014). doi: 10.1016/j.asr.2013.06.013
- 28.Yonetoku, D., Murakami, T., Masui, H., Kodaira, H., Aoyama, Y., et al.: Development of polarimeter for gamma-ray bursts onboard the solar-powered sail mission. In: Proceedings SPIE Conference, vol. 6266 (2006)Google Scholar