XSPECT on-board XPoSat: Calibration and First Results

TL;DR

This paper details the calibration process and initial results of XSPECT, India's first X-ray spectro-polarimetry instrument on the XPoSat mission, enabling long-term celestial source monitoring.

Contribution

It presents the first calibration and validation of XSPECT using on-ground and in-flight data, demonstrating its readiness for scientific observations.

Findings

Calibration validated with in-flight data

Instrument alignment and effective area refined

Initial spectro-temporal observations obtained

Abstract

XPoSat is India's first X-ray spectro-polarimetry mission, consisting of two co-aligned instruments, a polarimeter (POLIX) and a spectrometer (XSPECT), to study the X-ray emission from celestial sources. Since polarimetry is a photon-hungry technique, the mission is designed to observe sources for long integration times (~ few days to weeks). This provides an unique opportunity, enabling XSPECT to carry out long-term monitoring of sources, and study their spectro-temporal evolution. To ensure that the instrument is able to fulfill its scientific objectives, it was extensively calibrated on-ground. Post launch, these calibrations were validated using on-board observations. Additionally, some aspects of the instrument such as alignment and effective area were also derived and fine-tuned from in-flight data. In this paper, we describe the calibration of XSPECT instrument in detail, including some initial results derived from its data to establish its capabilities.