INDIA'S FIRST X-RAY POLARIMETRY MISSION:XPOSAT

Context

• ISRO's PSLV-C58 launched XPOSAT Satellite into an Eastward low inclination orbit on January 2024.

About Top of FormX-Ray Polarimeter Satellite (XPoSat)

1. XPoSat is India's inaugural polarimetry mission for studying cosmic X-ray polarization and dynamics of X-ray sources.
2. The spacecraft operates in Low Earth Orbit (~650 km altitude, ~6-degree inclination).
3. It is the world's second X-ray polarimetry mission after NASA's Imaging X-ray Polarimetry Explorer (IXPE) Mission.
4. The mission's lifespan is 5 years.
5. Two scientific payloads: X-Ray Polarimeter (POLIX) and X-ray SPECtroscopy and Timing (XSPECT).

POLIX	XSPECT
Measures polarimetry parameters (degree and angle) in the medium X-ray energy range (8-30 keV).	Provides spectroscopic information in the energy range of 0.8-15 keV.
Developed by the Raman Research Institute, Bengaluru.	Developed by the U.R. Rao Satellite Centre, ISRO.
	Observes various sources, including X-ray pulsars, blackhole binaries, low-magnetic field neutron stars, Active galactic nuclei, and Magnetars.

Objectives of the Mission

1. Measure X-ray polarisation (8-30 keV) from 50 cosmic sources via Thomson Scattering using POLIX payload.
2. Conduct long-term spectral and temporal studies (0.8-15 keV) of cosmic X-ray sources with XSPECT payload.
3. Perform polarisation and spectroscopic measurements of X-ray emissions in a common energy band using POLIX and XSPECT payloads.

Polarisation of Light

1. Light travels as transverse electromagnetic waves.
2. Unpolarised light from sources like the sun vibrates in multiple planes.
3. Polarisation restricts light waves' vibration to a specific direction/plane.
4. Polarimetry measures polarisation characteristics, aiding astronomers in observing and measuring various object properties.

Why X-rays?

1. X-rays, high-frequency and high-energy electromagnetic radiation, have short wavelengths (0.01 to 10 nanometres).
2. X-rays emanate from extremely hot objects, such as pulsars and black hole accretion disks.
3. Short X-ray wavelengths and high energy allow penetration of most materials, aiding in data collection from celestial sources.
4. X-ray telescopes in orbit collect photons from specific sky regions, providing insights into distant celestial environments' composition, temperature, and density.

Significance of the Mission

1. X-ray polarisation measurement aids in understanding X-ray emission in various astrophysical sources.
2. Black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae emit X-rays with complex mechanisms.
3. Combining polarimetric, spectroscopic, and timing measurements overcomes limitations in understanding astronomical emission processes.
4. Measuring X-ray polarisation deduces magnetic field orientation and strength in celestial objects.
5. Magnetic fields play a crucial role in astrophysical processes, including particle generation, acceleration, and jet formation.
6. X-ray polarisation helps understand high-energy particle behaviour in extreme environments.
7. X-rays in extreme conditions come from supernova remnants, active galactic nuclei, and gamma-ray bursts.

Techniques and Challenges

1. Developing precise X-ray polarimeters is challenging due to faint and complex X-ray signals.
2. Analysing polarised X-ray data requires sophisticated algorithms to interpret measurements.
3. Obtaining high-quality polarimetric data involves dealing with background noise and calibration issues.

Applications and Impact

1. Black Hole and Neutron Star Studies: Polarimetry aids in understanding extreme conditions near black holes and neutron stars.
2. Active Galactic Nuclei (AGN): Investigating X-ray polarisation helps unravel mechanisms behind AGN radiation and jet formations.
3. Cosmological Insights: Polarimetry of cosmic X-ray background radiation offers insights into the universe's early stages and evolution.

Conclusion

1. The XPoSat launch demonstrates India's commitment to advancing space science, specifically in X-ray astronomy.
2. This mission contributes significantly to understanding high-energy astrophysical phenomena, marking a crucial step in India's space research and exploration.

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