ISRO’s XPoSat Mission: Unraveling X-ray Polarimetry in Space

Introduction:

• On January 1, the Indian Space Research Organisation (ISRO) achieved a significant milestone by placing its inaugural X-ray Polarimeter Satellite (XPoSat) into a precise circular orbit approximately 650 kilometers above the Earth’s surface. This groundbreaking mission marks the world’s second endeavor specifically dedicated to conducting X-ray polarimetry measurements, offering profound insights into celestial sources’ polarized X-rays.

Mission Overview:

• XPoSat’s primary objective revolves around analyzing the polarization of X-rays emitted by bright celestial sources within the medium frequency band. The satellite integrates two crucial payloads, namely the Indian X-ray Polarimeter (POLIX) and X-ray Spectroscopy and Timing (XSPECT), developed by the Raman Research Institute and UR Rao Satellite Centre in Bengaluru.
• Operating in a low earth orbit with an inclination of approximately 6 degrees, XPoSat is slated for a mission duration of about five years. During this period, it will observe polarized X-rays emitted by magnetars, neutron stars, and other highly magnetic cosmic entities as they transit through the Earth’s shadow, particularly during eclipse phases.

Scientific Payloads:

• POLIX, a groundbreaking instrument, operates within the medium X-ray energy band of 8 to 30 kilo electron Volts (keV). It comprises essential components like a collimator and four X-ray proportional counter detectors, designed to observe numerous astronomical sources.
• XSPECT, on the other hand, specializes in fast timing and high-resolution spectroscopy within the soft X-ray energy band (0.8-15 keV). Its observations encompass a wide array of sources, including X-ray pulsars, black hole binaries, low-magnetic field neutron stars, active galactic nuclei (AGNs), and magnetars.

Significance of XPoSat:

• Traditionally, astronomers have relied on spectroscopy, imaging, and timing-based data acquired from ground-based telescopes or satellite missions across various electromagnetic spectrum bands. However, XPoSat marks a paradigm shift by enabling X-ray polarimetry measurements from bright sources within the 8-30 keV energy range, an unprecedented endeavor.
• This mission is poised to observe numerous X-ray radiating sources, categorizing them as persistent or transient. By studying polarized X-rays emanating from magnetars, black holes, and neutron stars, scientists anticipate unraveling the nature of these radiations and the underlying processes involved.

Understanding X-ray Polarization:

• X-rays, characterized by their constantly moving electric and magnetic waves, when polarized, exhibit organized motion with waves vibrating in the same direction. XPoSat’s measurements of angular and degree of polarization aim to decode the intricate processes undergone by X-rays as they interact with diverse materials in the Universe, shedding light on the nature of these emissions.

XPoSat in Global Context:

• Globally, missions focusing on X-ray polarimetry measurements have been limited. NASA’s IXPE operates within the soft X-ray band, complementing XPoSat’s efforts in the medium X-ray band. The unparalleled sensitivity and precision of XPoSat’s POLIX payload contribute significantly, expanding observational capabilities compared to previous missions.

Conclusion:

• XPoSat’s pioneering venture into X-ray polarimetry promises a deeper understanding of celestial bodies emitting X-rays, including black holes, neutron stars, and magnetars. By scrutinizing polarized X-rays within this previously unexplored energy range, the mission heralds a new era in space research, poised to unravel the mysteries of the Universe.