Using collimated CZTI as all sky X-ray detector based on Earth Occultation Technique

TL;DR

This paper demonstrates that the collimated CZTI instrument on AstroSat can be used as an all-sky X-ray detector employing the Earth occultation technique, enabling flux measurements of bright sources like Crab and Cyg X-1.

Contribution

First application of Earth occultation technique with a collimated detector (CZTI) on AstroSat for all-sky X-ray flux measurements.

Findings

Reliable flux measurements for Crab nebula, pulsar, and Cyg X-1.

CZTI can detect sources with intensities greater than approximately 1 Crab.

Demonstrates the feasibility of using collimated detectors for all-sky monitoring.

Abstract

All-sky monitors can measure the fluxes of astrophysical sources by measuring the changes in observed counts as the source is occulted by the Earth. Such measurements have typically been carried out by all-sky monitors like $\textit{CGRO}$-BATSE and $\textit{Fermi}$-GBM. We demonstrate for the first time the application of this technique to measure fluxes of sources using a collimated instrument: the Cadmium Zinc Telluride detector on $\textit{AstroSat}$. Reliable flux measurements are obtained for the Crab nebula and pulsar, and for Cyg X-1 by carefully selecting the best occultation data sets. We demonstrate that CZTI can obtain such measurements for hard sources with intensities $\gtrsim1$Crab.