After its successful sun, moon expeditions, Isro starts work on dedicated polarimetry mission
ISRO is preparing to launch its first polarimetry mission, XPoSat, by the end of the year. This will be the second polarimetry mission in the world
After the success of India’s Moon and Sun missions, the Indian Space Research Organisation (Isro) is now preparing for the country’s first (and world’s second) dedicated polarimetry mission to study various dynamics of bright astronomical X-ray sources in extreme conditions, providing vital information on the nature and behaviour of celestial objects. This mission is expected to be launched by the end of the year, scientists said.
“The dates for the XPoSat (X-ray Polarimeter Satellite) mission are yet to be finalised but the work around it is progressing at a fast pace,” Isro chairman S Somanath said.
XPoSat is India’s first and the world’s second space mission to measure the polarisation of light. Polarimetry is a powerful tool that allows astronomers to infer information about celestial objects, from passing comets to distant galaxies. Isro scientists explained that the mission is unique and crucial because it will help them understand and measure emissions from various astronomical sources — black holes, neutron stars, active galactic nuclei, pulsar wind nebulae — that are otherwise challenging to study.
Such emissions are mostly tracked by studying the chemical make up (using a spectroscope) and the time it takes them to travel a distance.
“While the spectroscopic and timing information by various space-based observatories provide a wealth of information, the exact nature of the emission from such sources still poses deeper challenges to astronomers. The polarimetry measurements add two more dimension to our understanding, the degree of polarization and the angle of polarization and thus is an excellent diagnostic tool to understand the emission processes from astronomical sources,” the space agency said.
The degree of polarization is the proportion of an electromagnetic wave that is polarized while the angle of polarization is the angle at which light of a certain polarization is perfectly transmitted through a transparent surface. Together, they can provide more information about the bodies that emit these waves.
Isro added: “The polarimetric observations along with spectroscopic measurements are expected to break the degeneracy of various theoretical models of astronomical emission processes. This would be the major direction of research from XPoSat by Indian science community.”
The mission will carry two payloads — POLIX (Polarimeter Instrument in X-rays) which will measure the polarimetry parameters including the degree and angle of polarization, in medium X-ray energy range of 8-30 keV photons of astronomical origin, and XSPECT (X-ray Spectroscopy and Timing) payload which will give spectroscopic information in the energy range of 0.8-15 keV.
The primary payload, POLIX, developed by the Bengaluru’s Raman Research Institute in collaboration with the UR Rao Satellite Centre (URSC) is made of a collimator, a device for producing a parallel beam of rays or radiation, a scatterer and four X-ray proportional counter detectors that surrounds the scatterer.
POLIX is expected to observe about 40 bright astronomical sources of different categories during its lifetime of about five years. This is the first payload in the medium X-ray energy band dedicated for polarimetry measurements.
XSPECT has been designed to provide fast timing and good spectroscopic resolution in soft x-rays. Taking advantage of the long duration observations required by POLIX to measure X-ray polarization, XSPECT will conduct long-term monitoring of spectral state changes in continuum emission, changes in their line flux and profile, simultaneous long term temporal monitoring of soft X-ray emission in the X-ray energy range 0.8-15 keV.
This will be the second such mission in the world, after the National Aeronautics and Space Administration’s (NASA’s) Imaging X-ray Polarimetry Explorer, or IXPE, which was built to “discover the secrets of some of the most extreme objects in the universe, the remnants of supernova explosions, powerful particle streams spit out by feeding black holes, and more.”
IXPE was NASA’s first mission to study the polarization of X-rays from many different types of celestial objects. Measuring the polarization of X-rays traces the story of where this light came from, including the geometry and inner workings of its source.
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