The AstroSat mass model: Imaging and flux studies of off-axis sources with CZTI

• DOI: 10.1007/s12036-021-09763-x
• Publication Date: 2021-08-02T15:03:30Z
• Authors: Sujay Mate; Tanmoy Chattopadhyay; Varun Bhalerao; E. Aarthy; Arvind Balasubram...; Dipankar Bhattach...; Soumya Gupta; Krishnan Kutty; N. P. S. Mithun; Sourav Palit; A. R. Rao; Divita Saraogi; Santosh Vadawale; Ajay Vibhute
• Keywords: Cadmium Zinc Telluride Imager; High Energy Astrophysical Phenomena (astro-ph.HE); [PHYS.PHYS.PHYS-INS-DET] Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det]; AstroSat; FOS: Physical sciences; Gamma-ray bursts; [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det]; [PHYS.ASTR] Physics [physics]/Astrophysics [astro-ph]; [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]; Astrophysics - Instrumentation and Methods for Astrophysics; Astrophysics - High Energy Astrophysical Phenomena; Instrumentation and Methods for Astrophysics (astro-ph.IM); mass model simulations

The Cadmium Zinc Telluride Imager (CZTI) on AstroSat is a hard X-ray coded-aperture mask instrument with a primary field of view of 4.6 x 4.6 degrees (FWHM). The instrument collimators become increasingly transparent at energies above $\sim$100 keV, making CZTI sensitive to radiation from the entire sky. While this has enabled CZTI to detect a large number of off-axis transient sources, calculating the source flux or spectrum requires knowledge of the direction and energy dependent attenuation of the radiation incident upon the detector. Here, we present a GEANT4-based mass model of CZTI and AstroSat that can be used to simulate the satellite response to the incident radiation, and to calculate an effective "response file" for converting the source counts into fluxes and spectra. We provide details of the geometry and interaction physics, and validate the model by comparing the simulations of imaging and flux studies with observations. Spectroscopic validation of the mass model is discussed in a companion paper, Chattopadhyay 2021.<br/>Accepted in the "AstroSat - 5 years" special issue of the Journal of Astrophysics and Astronomy<br/>