ISRO’s New Year Surprise: All you need to know about India’s XPoSat mission, why it is crucial for the country

The Indian Space Research Organisation (ISRO) is gearing up for a groundbreaking start to 2024 with the launch of its maiden X-ray Polarimeter Satellite (XPoSat), a space-based observatory designed to explore X-ray polarization and its cosmic sources, including celestial entities like black holes, neutron stars, and magnetars. Scheduled to lift off from the Satish Dhawan Space Centre in Sriharikota at 9:10 am on Monday, the PSLV-C58 rocket will carry the primary payload, XPoSat, along with 10 other satellites destined for deployment in low-earth orbits. XPoSat’s Mission XPoSat stands as the world’s second X-ray polarimetry mission, following NASA’s launch of the Imaging X-ray Polarimetry Explorer (IXPE) in 2021. Notably, XPoSat will operate within the medium X-ray band, distinguishing it from IXPE, which focuses on the soft X-ray band. If successful, India will secure its position as the second country globally to launch an advanced astronomy observatory dedicated to studying the intricate dynamics of bright astronomical X-ray sources, particularly black holes and neutron stars. XPoSat, India’s inaugural dedicated polarimetry mission, will orbit Earth in a low orbit and carry two scientific payloads. The primary payload, POLIX (Polarimeter Instrument in X-rays), will measure polarimetry parameters, including the degree and angle of polarization, in the medium X-ray energy range of 8-30 keV photons of astronomical origin. Additionally, the XSPECT (X-ray Spectroscopy and Timing) payload will provide spectroscopic information in the energy range of 0.8-15 keV. ISRO’s motivation behind launching this mission lies in the complexity of understanding the emission mechanisms from various astronomical sources, such as black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae. XPoSat Mission’s Objectives While existing space-based observatories offer valuable spectroscopic and timing information, the addition of polarimetry measurements, detailing the degree and angle of polarization, promises to enhance astronomers’ understanding of emission processes from these celestial sources. The combination of polarimetric and spectroscopic observations is anticipated to unravel challenges posed by various theoretical models of astronomical emission processes. The objectives of the XPoSat mission include measuring X-ray polarization in the energy band of 8-30 keV from around 50 potential cosmic sources, conducting long-term spectral and temporal studies of cosmic X-ray sources in the energy band of 0.8-15 keV, and performing polarimetry and spectroscopic measurements of X-ray emissions from cosmic sources within the common energy band. XPoSat’s instruments XPoSat carries two major instruments, POLIX and XSPECT, developed by the Raman Research Institute and the Space Astronomy Group of URSC, respectively. POLIX, focusing on the medium X-ray energy band, aims to observe approximately 40 bright astronomical sources of different categories during the planned five-year mission lifetime. On the other hand, XSPECT, specializing in soft X-rays, provides fast timing and excellent spectroscopic resolution, enabling long-term monitoring of spectral state changes in continuum emission, alterations in line flux and profile, and simultaneous temporal monitoring of soft X-ray emission in the 0.8-15 keV range. The XPoSat mission marks a significant step for the Indian science community, offering a unique avenue to deepen the understanding of cosmic phenomena through advanced observational techniques. (With inputs from agencies)