Engineering 101

Using X-ray Polarimetry in Space Exploration

An Imaging X-ray Polarimetry Explorer (IXPE) launched by NASA on 9 December 2021 is a space-based observatory. Developed with the Italian Space Agency (ASI), it has three identical telescopes, each with an imaging X-ray detector sensitive to light polarization at its focus. With it, IXPE can explore some of the brightest cosmic X-ray sources in our universe, such as pulsars, black holes, and neutron stars.

A recent article published in the Journal of Astronomical Telescopes, Instruments, and Systems provides a detailed description of the optics and detectors of IXPE and the mission’s scientific goals. Over a 2-year mission, IXPE will study dozens of X-ray sources in its first year and make more detailed observations of the chosen targets in the second year.

The observatory uses an array of 12 sun sensors, a three-axis magnetometer, and two star trackers to maintain its course in space. Each telescope comprises a mirror module assembly (MMA) that focuses X-rays into polarization-sensitive detector units (DUs). The detector units relay that information to the detector service unit (DSU), which processes the data and transmits it to the ground. A lightweight, coilable boom deployed after launch ensures the correct focal length and aligns the MMAs with the DUs. A tip-tilt-rotate mechanism exists onboard, which aligns the mirrors with the detectors as well.

The IXPE team expects that the most striking early images will likely come from shell-type supernova remnants. IXPE should also image active galaxies, the galactic center of the Milky Way galaxy, and “blazars,” a galaxy that emits powerful jets of ionized matter and radiation. This mission will push the envelope of observations even further by exploring new source types of particular interest to gain physical insights.

Read the open-access article by Weisskopf et al., “Imaging X-ray Polarimetry Explorer: prelaunch” J. of Astronomical Telescopes, Instruments, and Systems, 8(2), 026002 (2022) doi.org/10.1117/1.JATIS.8.2.026002.

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