Abstract
The Cadmium–Zinc–Telluride (CZT) Imager on board AstroSat is a hard X-ray imaging spectrometer operating in the energy range of 20–100 keV. It also acts as an open hard X-ray monitor above 100 keV capable of detecting transient events like the Gamma-ray Bursts (GRBs). Additionally, the instrument has the sensitivity to measure hard X-ray polarization in the energy range of 100–400 keV for bright on-axis sources like Crab and Cygnus X-1 and bright GRBs. As hard X-ray instruments like CZTI are sensitive to cosmic rays in addition to X-rays, it is required to identify and remove particle induced or other noise events and select events for scientific analysis of the data. The present CZTI data analysis pipeline includes algorithms for such event selection, but they have certain limitations. They were primarily designed for the analysis of data from persistent X-ray sources where the source flux is much less than the background and thus are not best suited for sources like GRBs. Here, we re-examine the characteristics of noise events in CZTI and present a generalized event selection method that caters to the analysis of data for all types of sources. The efficacy of the new method is reviewed by examining the Poissonian behavior of the selected events and the signal to noise ratio for GRBs.
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Acknowledgements
The data used in this work is from the AstroSat mission of the Indian Space Research Organization (ISRO), archived at the Indian Space Science Data Centre (ISSDC). We acknowledge the AstroSat CZTI Payload operation centre at IUCAA for their help in developing and testing this algorithm. The CZT Imager instrument was built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed and facilitated the project. We thank Mayuri Shinde for her contributions in developing the algorithm into a code in C++ programming language. We also thank Avinash Aher for his contributions in data analysis.
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This article is part of the Special Issue on “AstroSat: Five Years in Orbit”.
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Ratheesh, A., Rao, A.R., Mithun, N.P.S. et al. A generalized event selection algorithm for AstroSat CZT imager data. J Astrophys Astron 42, 37 (2021). https://doi.org/10.1007/s12036-021-09716-4
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DOI: https://doi.org/10.1007/s12036-021-09716-4