Moon, Sun, Now the Galaxy: ISRO’s XPoSat mission will unravel universe’s most puzzling mysteries

In a pioneering move aimed at advancing our understanding of the cosmos, the Indian Space Research Organisation (ISRO) has unveiled its latest project, the XPoSat (X-ray Polarimeter Satellite).

Following the successful launches of the Chandrayaan-3 Moon lander and Aditya-L1 missions, ISRO is now directing its attention toward unravelling the mysteries surrounding bright astronomical X-ray sources in extreme conditions.

Unravelling the cosmic mysteries of the star
The XPoSat mission represents India’s first dedicated polarimetry venture, with its primary goal being the investigation of various phenomena within luminous astronomical X-ray sources. Positioned in a low Earth orbit, this spacecraft will carry two crucial scientific instruments engineered to gather invaluable data.

The leading instrument, known as POLIX (Polarimeter Instrument in X-rays), has been meticulously designed to measure polarimetry parameters, including the degree and angle of polarization.

Its focus will be on the medium X-ray energy range, specifically targeting photons of astronomical origin within the 8-30 keV range. In tandem with POLIX, the XSPECT (X-ray Spectroscopy and Timing) instrument will play a vital role by providing spectroscopic data in the energy range of 0.8-15 keV.

What makes the XPoSat mission special
ISRO underscores that the emission mechanisms observed in various celestial sources, such as black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae, arise from intricate physical processes that challenge our current understanding.

While space-based observatories have yielded significant insights through spectroscopic and timing data, the precise nature of these emissions remains enigmatic, as acknowledged by ISRO officials.

“The inclusion of polarimetry measurements introduces two additional dimensions to our understanding: the degree of polarization and the angle of polarization. Consequently, it serves as a valuable diagnostic tool for comprehending the emission processes originating from astronomical sources,” explained ISRO.

The integration of polarimetric observations with spectroscopic measurements is anticipated to break down any barrier that is present by several theoretical models pertaining to astronomical emission processes. This amalgamation of data is poised to become the principal avenue of research for the Indian scientific community throughout the XPoSat mission.

The main payloads of the XPoSat
POLIX, functioning within the energy range of 8-30 keV, is comprised of a collimator, a scatterer, and four X-ray proportional counter detectors. The collimator narrows the field of view to 3 degrees by 3 degrees, ensuring that only one prominent source is observed at any given time during most observations.

POLIX’s mission will encompass the study of approximately 40 bright astronomical sources spanning various categories over the intended five-year duration of the XPoSat mission. This distinction marks it as the inaugural payload exclusively dedicated to polarimetry measurements within the medium X-ray energy band.

XSPECT, designated as the X-ray Spectroscopy and Timing payload, offers swift timing measurements and remarkable spectroscopic resolution in the realm of soft X-rays.

In tandem with POLIX’s extended observations for X-ray polarization measurement, XSPECT will facilitate continuous monitoring of spectral state fluctuations, modifications in line flux and profile, and concurrent, long-term temporal tracking of soft X-ray emissions within the energy range of 0.8-15 keV.

XSPECT’s targeted sources encompass a spectrum of celestial objects, including X-ray pulsars, black hole binaries, low-magnetic field neutron stars (NS) within low-mass X-ray binaries (LMXBs), active galactic nuclei (AGNs), and Magnetars.