Experimental verification of off-axis polarimetry with Cadmium Zinc Telluride detectors of AstroSat-CZT Imager

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 laun...

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Hauptverfasser: Vaishnava, C. S, Mithun, N. P. S, Vadawale, Santosh V, Aarthy, Esakkiappan, Patel, Arpit R, Adalja, Hiteshkumar L, Tiwari, Neeraj Kumar, Ladiya, Tinkal, Navale, Nilam, Chattopadhyay, Tanmoy, Rao, A. R, Bhalerao, Varun, Bhattacharya, Dipankar
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Sprache:eng
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Zusammenfassung: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.
DOI:10.48550/arxiv.2209.00222