Abstract Details

Name: Ajay Vibhute
Affiliation: IUCAA
Conference ID: ASI2021_337
Title : Statistical estimation of source properties for indirect imaging methods in Astronomy
Authors and Co-Authors : Ajay Vibhute (IUCAA, Pune), Prof. Dipankar Bhattacharya (IUCAA, Pune)
Abstract Type : Oral
Abstract Category : Thesis
Abstract : The direct imaging techniques based on reflective optics are not available at higher energies, but indirect imaging methods allow observing the sky at higher energies. One such indirect imaging technique, addressed in this thesis is Coded Mask Imaging. Coded Mask Imaging is an ideal technique to observe the sky for hard X-ray sources. Coded Mask telescopes provide larger Field of View (FOV) and allow simultaneous measurement of source and background signals. India’s first dedicated astronomical observatory AstroSat employs two coded mask telescopes, namely the Cadmium Zinc Telluride Imager (CZTI) and the Scanning Sky Monitor (SSM) to observe the sky for high energy X-ray sources. An essential part of the coded mask instrument's operations involves ground calibration, in-flight calibration, and performance verification. Coded Mask imaging requires special methods for image and spectrum reconstruction. This thesis presents various image reconstruction methods implemented to carry out CZTI on-ground, in-orbit imaging calibration, and calibration results. The mask weighting is one commonly used spectrum reconstruction technique used for coded mask instruments. In mask weighting, each photon is assigned a weight proportional to the probability of photon belonging to the target source. Such weighting techniques work well only if there is a single strong source present in the FOV. In reality, there can be many strong sources in FOV. In this thesis, we propose a spectrum reconstruction technique based on Bayesian inference to reconstruct the spectrum of the sources in a crowded field. CZTI acts as an open sky detector at higher energies and allows transient events detection. To extract the signature of such transients from the CZTI data in a fast and uniform manner, we have developed an automated method which we present in this thesis.