The Daksha Mass Model: estimating background counts and exploring Compton imaging for a highly sensitive high energy space telescope

The upcoming Daksha mission aims to be the workhorse for monitoring electromagnetic counterparts of gravitational sources from the entire sky. It will have unprecedented temporal and spatial coverage of the sky in full energy range of X-rays and low energy gamma rays ($\sim$ 1 keV up to >1 MeV) with fair (few degrees) localization capability. Being an all-sky monitor, most of the detectors of the satellite will be fully exposed to and unprotected from any types of unwanted space radiation. Moreover, the unprecedented sensitivity of the satellite towards detecting and localizing fainter and far away transient sources than those detected by any existing satellites of the same class, will require efficient X-ray background subtraction mechanism and hence prior and precise knowledge of the background count rates. Here we present, in detail, the outcome of GEANT4 Monte Carlo simulation, performed for estimating background count rates at different types of detectors used in the mission. Medium energy Cadmium Zinc Telluride (CZT) detectors and high energy Sodium Iodide (NaI) scintillator detectors, used in the satellite, will be simultaneously employed as parts of Compton imager for transient source localization. Here, we also present the results of our state-of-the-art simulation with MEGAlib Monte Carlo simulation code to explore the Compton imaging capabilities of the satellite.