After a highly productive 2023, with the successful launch of third Lunar Mission Chandrayaan-3 and the first Sun exploratory Aditya-L1, a buoyant Indian Space Research Organisation (ISRO) will usher in 2024 with the launch of PSLV-C58/X-ray Polarimeter Satellite (XPoSat) mission on January one from the spaceport of Sriharikota. The New year day mission will take place from the First Launch Pad at 0910 hrs, ISRO sources said on Thursday. This mission aims to investigate the polarization of cosmic X-rays. This X-ray Polarimeter Satellite (XPoSat) mission comes in the backdrop of the success of Chandrayaan-3 mission, when them spacecraft landed in the Moon’s south polar region and the successful launch of first solar observation mission Aditya L1 this year with the spacecraft all set to reach the L1 point on January six to explore the outer atmosphere of the sun. This Xpost satellite is designed to remain operational for a minimum of five years and will be used to observe pulsars, X-ray binaries involving black holes, active galactic nuclei, and non-thermal supernova remnants.
ISRO said the first X-Ray Polarimeter Satellite (XPoSat) is aiming to investigate the polarization of intense X-Ray sources. While space-based X-Ray astronomy has been established in India, focusing predominantly on imaging, time-domain studies, and spectroscopy, this upcoming mission marks a major value-addition. The astronomy community is particularly enthused about the prospect of a systematic exploration into the polarization of X-Rays emitted by astronomical sources. This research, supplementing traditional time and frequency domain studies, introduces a novel dimension to X-Ray astronomy, generating anticipation and excitement within the scientific community. The XPoSat spacecraft is designated for observation from Low Earth Orbit (non-sun synchronous orbit of 650 km altitude, low inclination of 6 degree), carrying two scientific payloads. With the two payloads, the XPoSat mission is capable of simultaneous studies of temporal, spectral, and polarization features of the bright X-Ray sources. The mission objectives include measurement of X-Ray polarization in the energy band of 8-30 keV emanated from X-Ray sources and long-term spectral and temporal studies of cosmic X-Ray sources in the energy band of 0.8-15 keV.
The mission life is expected to be 5 years. The payloads onboard XPoSat will observe the X-Ray sources during its transit through the Earth’s shadow, i.e., during the eclipse period. The primary payload of XPoSat, POLIX (Polarimeter Instrument in X-rays), is designed to measure polarimetry parameters—specifically the degree and angle of polarization—in the medium X-ray energy range of 8-30 keV photons originating from astronomical sources. Complementing this, the XSPECT (X-ray Spectroscopy and Timing) payload will provide spectroscopic information within the energy range of 0.8-15 keV. The POLIX payload is developed by the Raman Research Institute (RRI), Bangalore, with support from the ISRO centres. The XSPECT payload is developed by the U R Rao Satellite Centre (URSC), ISRO. The POLIX payload serves as an X-ray Polarimeter designed for astronomical observations within the energy band of 8-30 keV.
The instrument comprises a collimator, a scatterer, and four X-ray proportional counter detectors surrounding the scatterer. The scatterer, constructed from low atomic mass material, induces anisotropic Thomson scattering of incoming polarized X-rays. The collimator plays a crucial role in restricting the field of view to 3 degrees by 3 degrees, ensuring that only one bright source is within the field of view for most observations. POLIX’s primary objective is to observe bright astronomical sources across various categories during the planned 5-year lifetime of the XPoSat mission. Notably, POLIX stands out as the first payload in the medium X-ray energy band specifically dedicated to polarimetry measurements. XSPECT is an X-ray Spectroscopy and Timing instrument, designed to offer fast timing and excellent spectroscopic resolution in soft X-rays (0.8-15 keV). XSPECT also monitors changes in line flux and profile, offering simultaneous, long-term temporal monitoring of soft X-ray emission. The instrument employs an array of Swept Charge Devices (SCDs) with an effective area exceeding 30 cm² at 6 keV and an impressive energy resolution of less than 200 eV at 6 keV. XSPECT employs passive collimators to reduce background by narrowing its field of view. This payload is anticipated to observe a variety of sources, including X-ray pulsars, black hole binaries, low-magnetic field neutron stars (NS), active galactic nuclei (AGNs), and magnetars.