ISRO-XPOSAT LAUNCH: New Year, New Mission
India’s X-Ray Polarimetry Astronomy Endeavourset for Launch on January 1, 2024
By R. Anil Kumar
Bangalore, December 28. India’s Space Agency, ISRO, is poised to start 2024 with a roaring launch of the Polar Satellite Launch Vehicle carrying the country’s first X-Ray Polarimeter Satellite (XPoSat) on January 1, 2024.
The Indian Space Research Organisation (Isro) has announced that the XPoSat mission will lift off at 9:10 am using a Polar Satellite Launch Vehicle (PSLV), marking a significant milestone in India’s space exploration journey.
The XPoSat mission is designed to investigate the polarisation of intense X-ray sources, a scientific endeavour that will place India at the forefront of space-based polarimetry.
This mission is not only India’s first dedicated polarimetry mission but also the world’s second, following Nasa’s Imaging X-ray Polarimetry Explorer (IXPE) launched in 2021.
India is set to launch its first X-Ray Polarimeter Satellite (XPoSat), aiming to investigate the polarization of intense X-Ray sources.
While space-based X-Ray astronomy has been established in India, focusing predominantly on imaging, time-domain studies, and spectroscopy, this upcoming mission marks a major value-addition.
The astronomy community is particularly enthused about the prospect of a systematic exploration into the polarization of X-Rays emitted by astronomical sources.
This research, supplementing traditional time and frequency domain studies, introduces a novel dimension to X-Ray astronomy, generating anticipation and excitement within the scientific community.
The XPoSat spacecraft is designated for observation from Low Earth Orbit (non-sun synchronous orbit of 650 km altitude, low inclination of 6 degree), carrying two scientific payloads.
With these two payloads, the XPoSat mission is capable of simultaneous studies of temporal, spectral, and polarization features of the bright X-Ray sources.
The mission objectives include (1) measurement of X-Ray polarization in the energy band of 8-30 keV emanated from X-Ray sources, (2) long-term spectral and temporal studies of cosmic X-Ray sources in the energy band of 0.8-15 keV. The mission life is expected to be 5 years. The payloads onboard XPoSat will observe the X-Ray sources during its transit through the Earth’s shadow, i.e., during the eclipse period.
At this juncture, in order to appreciate the importance of this mission, it is apt to take a retrospective look of the evolution of astronomical instrumentation and gradual unfurling of the mysteries in the cosmos.
It all started with the invention of optical telescope, more than four hundred years ago. Even our initial encounter with Astronomy,often involved optical telescopes, observing the Moon’s features and planets in our solar system.
Ray polarization serves as a crucial diagnostic tool for examining the radiation mechanism and geometry of celestial sources.
Analyzing X-Ray polarization signatures enables measurements of the mass and spin of accreting black holes, comprehension of the source’s geometric arrangement and local properties, exploration of accretion flow, outflow, and jets, investigation into the nature of X-Ray scattering and reflection mediums, estimation of strong magnetic fields, and revelation of the radiation zone and particle acceleration processes in pulsars, among other applications.
Each of these processes manifests its distinct signature within appropriate energy bands, depending on the involved energetics. The XPoSat mission by ISRO is specifically designed to investigate such X-Ray polarization signatures emanating from bright X-Ray sources.
XPoSat aims to study the 50 brightest known sources in the universe, including pulsars, black hole X-ray binaries, active galactic nuclei, neutron stars, and non-thermal supernova remnants.
The satellite will be placed in a circular low Earth orbit of 500–700 km, with a mission lifespan of at least five years.
The primary payload, POLIX (Polarimeter Instrument in X-rays), will measure the degree and angle of polarization in the medium X-ray energy range of 8-30 keV photons of astronomical origin. Complementing POLIX, the XSPECT (X-ray Spectroscopy and Timing) payload will provide spectroscopic information in the energy range of 0.8-15 keV.
Developed by the Raman Research Institute (RRI) in collaboration with U R Rao Satellite Centre (URSC), these instruments are expected to offer new insights into the physics of celestial objects.
By measuring the polarisation of X-rays, scientists can infer critical information about the geometry and emission mechanisms of these distant sources.
The XPoSat mission is anticipated to break new ground in our understanding of the universe. It will add two crucial dimensions — degree and angle of polarization—to the existing spectroscopic and timing data, potentially resolving ambiguities in current theoretical models of astronomical emissions.
