March 1, 2024

Lukmaan IAS

A Blog for IAS Examination




THE CONTEXT: Recently, Indian Space Research Organisation (ISRO) put its first polarimetry mission X-ray Polarimeter Satellite (XPoSat) in a precise circular orbit of 650 km after a 21-minute flight.


  • ISRO (Indian Space Research Organisation) has launched XPoSat, India’s pioneering satellite-based mission exclusively dedicated to conducting X-ray polarimetry measurements.
  • This mission holds global significance as the second such satellite-based initiative worldwide.

Objectives and Payloads:

  • XPoSat aims to analyze the polarization of X-rays emitted from celestial sources within the medium frequency band.
  • The satellite comprises two primary payloads:
  • Payloads were developed by the Raman Research Institute and UR Rao Satellite Centre, both located in Bengaluru.
  • Satellite has been positioned in a low earth orbit of approximately 650 km with a low inclination of about 6 degrees, XPoSat anticipates a mission life of around five years.
  • The satellite’s observations primarily focus on polarized X-rays emitted from magnetars or neutron stars while transiting Earth’s shadow, especially during eclipse periods.

Scientific Significance of XPoSat:

  • This mission marks a significant advancement in space-based X-ray polarimetry, an area less explored compared to other spectrums of the electromagnetic spectrum.
  • Unlike traditional methods using spectroscopy, imaging, and timing data, XPoSat enables the measurement of polarized X-rays emitted from various celestial sources, providing a deeper understanding of magnetars, black holes, and neutron stars.

Role of POLIX and XSPECT Payloads:

  • POLIX:
    • World’s first instrument designed for operation in the medium X-ray energy band (8 to 30 keV).
    • It utilizes a collimator and four X-ray proportional counter detectors to observe selected astronomical sources, particularly those surrounded by bright sources in the field of view.
    • Engineered for fast timing and high spectroscopic resolution within the soft X-ray energy band (0.8-15 keV).
    • It observes a diverse range of celestial sources, including X-ray pulsars, black hole binaries, and active galactic nuclei.

Importance of X-ray Polarization Studies:

  • Studying polarized X-rays from cosmic sources offers insights into the nature of radiations and the underlying processes contributing to their generation.
  • For instance, interactions with strong magnetic fields or materials around black holes can polarize X-rays.
  • Investigating polarized X-rays can unlock mysteries surrounding the behaviour and composition of celestial bodies.

Comparison with Global X-ray Missions:

  • XPoSat joins a limited number of missions dedicated to X-ray polarimetry measurements.
  • While NASA launched balloon-based experiments like HX-POL and XL-Calibur, the Indian AstroSat mission previously conducted timing and spectroscopy of X-ray sources but did not include polarisation studies.
  • In 2021, NASA introduced the Imaging X-ray Polarimetry Explorer (IXPE) focusing on soft X-ray band measurements (2 to 8 keV), while XPoSat extends the observational energy band into the medium X-ray range (8 to 30 keV).


  • ISRO’s XPoSat mission signifies a groundbreaking leap in X-ray polarimetry studies, enhancing our understanding of celestial phenomena emitting X-rays.
  • By probing the polarization of X-rays from magnetars, black holes, and neutron stars, XPoSat’s POLIX and XSPECT payloads aim to unravel mysteries and contribute significantly to the broader understanding of the Universe’s enigmatic cosmic bodies.
  • The innovative capabilities of XPoSat’s payloads pave the way for new avenues in space research, enabling detailed investigations and potentially reshaping existing paradigms in the study of high-energy astrophysics.


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