The X-ray Polarimetry Satellite (XPoSat) mission was launched on January 1, 2024 on the ISRO’s PSLV rocket from India’s Satish Dhawan Space Centre. It has been placed in its final circular 350 km orbit for observations. The XPoSat mission carires two instruments: the Polarimter Instrument in X-rays (POLIX) made by the Raman Research Institute, and the X-ray Spectroscopy and Timing (XSPECT) from the Space Astronomy Group at U R Rao Satellite Centre (USRC).

The observatory will perform pointed polarimetry measurements of about 50 of the brightest astronomical X-ray sources using POLIX. The secondary XSPECT instrument will conduct timing and spectroscopy studies, with its soft X-ray detections complementing the higher energy range Large Area X-ray Proportional Counter (LAXPC) on AstroSat.

Mission Characteristics

Lifetime

Angular resolution:

Energy Range

Special Features

Payload

• Polarimeter Instrument in X-rays (POLIX) is the primary scientific payload with a Thompson scattering X-ray polarimeter for X-rays in the 8–30 keV range. It consists of a collimator, a central low-Z (lithium/beryllium) target to scatter incident X-ray photons, and a set of four Xenon-filled wire frame X-ray detectors mounted around the instrument assembly. The entire satellite is rotated around the viewing axis to observe the source at different azimuthal angles, spinning at approximately 0.2 RPM with long (1–4 weeks) observations on each source.
  
  • Minimum linear polarization degree: 2-3%
    
  • Field of view: 3°×3°
    
  • Effective area: 650 cm²
    
• X-ray Spectroscopy and Timing (XSPECT) is co-aligned with POLIX, observing the same source to provide timing and spectral measurements in the 0.8–15 keV energy range with long duration observations. The detectors consist of large area Swept Charge Devices (SCD), a variant of traditional X-ray CCDs. SCDs permit fast readout times (10-100 kHz) and passive cooling.
  
  • Field of view: 1°×1°
    
  • Detector sensitive area: 64 cm²
    
  • Timing resolution: ~2 ms
    
  • Energy resolution: <200 eV @ 5.9 keV
    

Science Goals

• Observe accreting galactic black holes to test aspects of General Relativity not observable by other means;
• Characterize the strength, distribution, and orientation of magnetic field stuctures in extreme astronomical objects (SNRs, AGN jets, micro-quasars).