January 11, 2024

The XSPECT payload on XPoSat, India's first X-ray polarimetric mission, has captured its first light from the Cassiopeia A (Cas A) supernova remnant. Launched on January 1, 2024, XPoSat carries two co-aligned instruments, POLarimeter Instrument in X-rays (POLIX) and X-ray SPECtroscopy and Timing (XSPECT), aimed at unravelling the mysteries of cosmic X-ray sources. While the POLIX instrument focuses on investigating X-ray polarization in medium-energy X-rays, the XSPECT payload, engages in continuous and long-term spectral and temporal studies of X-ray sources in the soft X-ray band.

During its performance verification phase, XSPECT was directed towards Cassiopeia A, a standard celestial source used for instrument evaluation. The observation commenced on January 5, 2024, capturing the supernova remnant's emission lines corresponding to elements such as Magnesium, Silicon, Sulphur, Argon, Calcium, and Iron.

Figure 1: XSPECT sees supernova remnant Cassiopeia A (Cas A). The spectrum includes both Galactic Cosmic Ray (GCR) background and Cosmic X-ray Background (CXB). The flux above 8 keV is mainly due to both CXB and GCR. The spectrum shown in Figure is for a total integration time of 20 ksec collected over multiple orbits.

XSPECT payload is developed by the Space Astronomy Group of U R Rao Satellite Centre (URSC)/ISRO, Bengaluru. The continuous observations facilitated by XSPECT's long-duration capabilities are anticipated to contribute significantly to our understanding of the universe's high-energy phenomena.