Isro launches X-ray polarimeter to gain insights from celestial sources

The Indian Space Research Organization (Isro) successfully launched the X-ray polarimeter satellite on the very first day of the new year, continuing its stellar space journey of the previous year.

The satellite, which was launched as scheduled from the Sriharikota spaceport on Monday at 9.10 am, would, among other things, provide insight into space-based polarization measurements of X-rays from various celestial sources.

Isro's PSLV-C58 mission is to launch the XPOSAT satellite in an easterly, low-inclination orbit. After injection of XPOSAT, the PS4 stage is restarted twice to reduce the orbit to a circular orbit of 350 km to maintain the 3-axis stabilized mode for Orbital Platform (OP) experiments. The PSLV Orbital Experimental Module-3 (POEM-3) experiment will be conducted meeting the target of 10 identified payloads provided by Isro and IN-SPACe.

The XPOSat (X-ray Polarimeter Satellite) is India's first dedicated polarimetry mission to study the various dynamics of bright astronomical X-ray sources under extreme conditions.

According to Isro, the XPOSAT satellite has two payloads:

POLIX: This will measure the polarimetry parameters (degree and angle of polarization) in the average X-ray energy range of 8-30 keV photons of astronomical origin. The payload is being developed by Ramam Research Institute (RRI), Bangalore, in collaboration with UR Rao Satellite Center (URSC). The instrument consists of a collimator, a scatterer and four proportional X-ray detectors surrounding the scatterer. The scatterer is made of low atomic mass material that causes anisotropic Thomson scattering of incoming polarized X-rays. The collimator limits the field of view to 3 degrees x 3 degrees, so that for most observations there is only one bright source in the field of view. POLIX is expected to observe approximately 40 bright astronomical sources of various categories during the XPoSat mission's planned lifetime of approximately 5 years. This is the first charge in the medium X-ray energy band specifically intended for polarimetry measurements.

XSPECT: Provides spectroscopic information in the energy range 0.8-15 keV. An X-ray spectroscopy and timing payload onboard XPoSat, which can provide fast timing and good spectroscopic resolution in soft X-rays. By using the long-term observations that POLIX needs to measure X-ray polarization, XSPECT can provide long-term monitoring of spectral state changes in continuum emission, changes in their line flux and profile, and simultaneous long-term temporal monitoring of soft X-ray emission in the ,8-15 keV. A range of Swept Charge Devices (SCDs) offer an effective area >30 cm2 at 6 keV with energy resolution better than 200 eV at 6 keV. Passive collimators are used to reduce background by narrowing the field of view of XSPECT. XSPECT would observe different types of sources, namely X-ray pulsars, black hole binaries, low magnetic field (NS) neutron stars in LMXBs, AGNs and Magnetars.

The aim of the mission is to measure the polarization of X-rays in the energy band 8-30keV from approximately 50 potential cosmic sources via Thomson scattering by POLIX payload. Performing long-term spectral and temporal studies of cosmic X-ray sources in the energy band 0.8-15 keV using XSPECT payload. Performing polarization and spectroscopic measurements of X-rays from cosmic sources by POLIX and XSPECT charges in the common energy band, respectively.

The emission mechanism of various astronomical sources such as black holes, neutron stars, active galactic nuclei, pulsar wind nebulae, etc. arises from complex physical processes and is challenging to understand. The exact nature of the emission from such sources continues to pose greater challenges to astronomers. The polarimetry measurements add two more dimensions to the understanding: the degree of polarization and the polarization angle, and are thus a diagnostic tool for understanding the emission processes of astronomical sources.

In a stunning display of prowess, India soared to new heights in 2023 with the successful soft landing of Chandrayaan-3 on the moon's south pole and the launch of Aditya-L1, India's first solar mission.

The primary objective of Chandrayaan-3, the country's first successful lunar landing mission, was to demonstrate a soft landing near the moon's south polar region and conduct experiments using the instruments on board the lander 'Vikram' and the robber 'Pragyaan'.

On August 23, Vikram Lander made his historic landing on the moon and then the Pragyan rover was deployed to explore the moon's unknown south pole.

These milestones have not only secured India's position in the global space economy but have also fueled the engines of India's private space sector.

Among the other achievements India is now pursuing include the Gaganyaan mission, setting up 'Bharatiya Antariksha Station' by 2035 and sending the first Indian to the moon by 2040.

First print: January 1, 2024 | 9:47 am IST