XPoSat Mission

What’s in today’s article?

•  Why in news?
• What is polarisation of X-rays?
• What is X-ray Polarimeter Satellite (XPoSat)?
• Significance of XPoSat Mission
• How does XPoSat compare with X-ray experiments or missions globally?

Why in news?

• Indian Space Research Organisation (ISRO) put its first polarimetry mission X-ray Polarimeter Satellite (XPoSat) on January 1.
  • ISRO’s PSLV-C58 has launched XPOSAT Satellite.
• XPoSat is the world’s second satellite-based mission dedicated to making X-ray polarimetry measurements.

Polarisation of X-rays

• About
  • X-rays comprise electric and magnetic waves that are constantly in motion. Being sinusoidal waves, they do not follow a patterned direction of motion.
  • Whereas, a polarised X-ray is both organised and has two waves vibrating in the same direction.
• Sources that emit polarised X-rays
  • When magnetars or black holes emit X-rays, they encounter a wide variety of materials in the Universe.
  • As X-rays pass through the thick cloud of materials, the electric component of the X-ray emits a photon in a changed direction, as it has now undergone scattering.
  • In the process, the new photon has got polarised in a direction perpendicular to the plane formed between the original and scattered photon.
• Polarisation measurements
  • The polarisation measurements – angular and degree of polarisation – are believed to provide clues about:
    • the bright X-ray emitting sources the nature of these radiations and
    • the complex process they undergo.

X-ray Polarimeter Satellite (XPoSat)

• About
  • It is the first dedicated satellite from ISRO to carry out research in space-based polarisation measurements of X-ray emission from celestial sources.
  • It is designated for observation from low earth orbit (~ 650 km, low inclination of ~ 6 degree).
  • It has an estimated mission life of about five years during which XPoSat will observe sources that emit polarised X-rays.
  • The observations will be done when the magnetars or neutron stars (they are highly magnetic and display a wide array of X-ray activity) are in transit through the Earth’s shadow, for instance, during the eclipse period.
• Scientific payloads onboard XPoSat
  • XPoSat comprises two payloads, including Indian X-ray Polarimeter (POLIX) and X-ray Spectroscopy and Timing (XSPECT).
  • They have been built by Raman Research Institute and UR Rao Satellite Centre, both located in Bengaluru.
  • POLIX:
    • It is the world’s first instrument designed to operate in the medium X-ray of 8 to 30 kilo electron Volt (keV) energy band.
    • It comprises a collimator, which is the key component to filter light originating from bright sources in the field of view.
    • Moreover, there is a scatterer consisting of four X-ray proportional counter detectors (that prevent the trapped light from escaping).
    • It will observe a few tens of astronomical sources. It was conceived, designed, and built at RRI.
  • XSPECT:
    • It is designed to conduct fast timing and high spectroscopic resolution in a soft X-ray energy band (0.8-15 keV).
    • It will observe a variety of sources like X-ray pulsars, black hole binaries, low-magnetic field neutron stars, active galactic nuclei or AGNs and magnetars.
      • AGNs are a compact region at the centre of a galaxy that emits a significant amount of energy across the electromagnetic spectrum.

Significance of XPoSat Mission

• X-ray polarisation measurements in medium energy bands for the first time
  • So far, polarisation of celestial sources was done either in the optical or radio bands.
  • XPoSat, however, will facilitate X-ray polarisation measurements possible from bright sources, that too, in the medium energy band (8-30 keV) energy range.
    • This has never been attempted ever before.
• Analyse two kinds of sources
  • XPoSat will observe two kinds of sources — persistent sources (targeted and known sources) and transient sources (pulsars, active galactic nuclei, magnetars).
• Nature of the radiations and the multitudes of processes involved can be analysed
  • Out in space, X-rays get polarised due to multiple causes.
    • For example, X-rays when subject to strong magnetic fields or due to the interactions with material present around black holes.
  • With the help of XPoSat, scientists can now probe the nature of the radiations and the multitudes of processes involved in the generation of these radiations.
• Will aid the researchers by analysing the additional parameters
  • POLIX will undertake important measurements like the degree and angle of polarisation of X-ray photons from various potential sources.
  • These two additional parameters, along with the spectrographic, timing and imaging data, will aid researchers to overall improve the present understanding of the celestial bodies.

How does XPoSat compare with X-ray experiments or missions globally?

• Indian astronomers, using AstroSat performed timing and broadband spectroscopy of X-ray sources but no polarisation studies were performed.
  • AstroSat is India’s first astronomy-based space missions that was launched in September 2015.
• The lack of development of highly sensitive and precise instruments makes missions for polarisation measurements of X-rays extremely challenging.
• In 2021, NASA launched Imaging X-ray Polarimetry Explorer (IXPE).
  • It has been designed to operate and perform X-ray polarisation measurements within the soft X-ray band (2 to 8 keV energy band).
• Besides complementing IXPE, XPoSat’s payload POLIX will offer an expanded observational energy band, as it is designated to perform X-ray polarisation in the medium X-ray band (8 to 30keV).

Q1) What is magnetars?

Magnetars are a type of neutron star with extremely strong magnetic fields. The magnetic field decay of magnetars powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.

Q2) What are X-rays? 

X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body.

Source: ISRO launches XPoSat: What is the mission and its significance? | ISRO

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