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The Indian X-ray Polarimeter (POLIX), onboard India’s X-ray polarimetry mission XPoSat, has commenced its scientific observations. A pulse profile of the Crab pulsar is generated from the observations carried out by POLIX during January 15-18, 2024. The Crab pulsar, a pulsating star, resides near the center of the Crab Nebula and spins about its axis approximately 30 times per second.

The plot illustrates the time window of X-rays scattered by the Beryllium scatterer inside POLIX, originally emitted from the Crab pulsar. This plot represents the first of its kind in this energy range. The data in lower and greater than this energy range are available from different missions. The X-axis indicates the time for two pulses, about 67 ms in total.

The plot also has the timing of non-pulsed emission components from the Pulsar Wind Nebula surrounding the pulsar. The time window facilitates determining the X-rays emitted from the pulsar (but not from the wind nebula). The polarization of X-rays from the source is detectable as the degree of asymmetry in the scattering of X-rays in the instrument depends on the polarization of the incoming X-rays.

The POLIX payload was activated in two stages by January 10, 2024, and initial scan observations were conducted around the Crab pulsar, the intended first target. The data plotted was collected during January 15-18, 2024, and thoroughly reviewed for confirmation. The data aligns with expectations.

This initial observation is a significant milestone for POLIX, showcasing its functionality and readiness for investigating pulsars, black holes, and other astronomical sources. As the sole payload offering data in this energy band, POLIX is poised to offer unique insights and contribute to understanding the physical processes associated with Astronomical X-ray sources.

POLIX was designed and developed by the X-ray Astronomy Laboratory at Raman Research Institute, Bengaluru. The instrument is built indigenously with the support from Indian industry.

The other instrument, XSPECT , onboard XPoSat is ready for observations.