ISRO Set to Launch India’s First X-ray Polarimetry Mission – XPoSat

Bengaluru: India’s space agency, ISRO, is set to launch the XPoSat (X-ray Polarimeter Satellite) mission, a significant step in advancing scientific understanding in the field of astronomy. This mission comes after the success of Chandrayaan-3 and Aditya-L1 ventures.

XPoSat is India’s inaugural dedicated polarimetry mission, designed to explore the behavior of bright astronomical X-ray sources in extreme conditions. It will operate in a low Earth orbit and carry two scientific payloads.

The primary payload, POLIX (Polarimeter Instrument in X-rays), will focus on measuring the polarization parameters, including the degree and angle of polarization, in the medium X-ray energy range of 8-30 keV photons originating from astronomical sources. Meanwhile, the XSPECT (X-ray Spectroscopy and Timing) payload will provide spectroscopic information within the energy range of 0.8-15 keV.

The significance of this mission lies in its ability to shed light on the complex emission mechanisms from celestial sources like black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae. These mechanisms have long puzzled astronomers due to their intricate nature.

While previous space-based observatories have offered valuable spectroscopic and timing data, polarimetry measurements introduce two new dimensions: the degree and angle of polarization. These measurements serve as a powerful diagnostic tool, enabling a deeper understanding of the emission processes from these astronomical sources.

By combining polarimetric observations with spectroscopic data, XPoSat is expected to resolve the ambiguities present in various theoretical models of astronomical emission processes. This mission will pave the way for significant research in the Indian scientific community.

POLIX, operating in the energy band of 8-30 keV, comprises a collimator, a scatterer, and four X-ray proportional counter detectors. It selectively observes about 40 bright astronomical sources of diverse categories during XPoSat’s planned five-year mission, making it the first payload in the medium X-ray energy band dedicated to polarimetry measurements.

XSPECT, on the other hand, is an X-ray spectroscopy and timing payload that offers fast timing and excellent spectroscopic resolution in soft X-rays. It will continuously monitor spectral state changes, line flux, and profiles, as well as long-term temporal variations in soft X-ray emissions across various source types, including X-ray pulsars, black hole binaries, low-magnetic field neutron stars, AGNs, and magnetars.