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The Rocket Experiment Demonstration of a Soft X-ray Polarimeter

Presentation #103.67 in the session Missions and Instruments.

Published onJul 01, 2023
The Rocket Experiment Demonstration of a Soft X-ray Polarimeter

We will report on the status of the Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX Polarimeter, name used with permission of Major League Baseball), a newly approved NASA mission. The goal of the project is to make the first measurement of the linear X-ray polarization in the 0.2-0.4 keV band. The first flight of the REDSoX Polarimeter would target Mk 421, which is commonly modeled as a highly relativistic jet aimed nearly along the line of sight. The instrument is designed to detect polarization as high as 16%. A neutron star with a strong magnetic field would be the target for a future flight. We employ multilayer-coated mirrors as Bragg reflectors at the Brewster angle. By matching to the dispersion of a spectrometer, one may take advantage of high multilayer reflectivities and achieve polarization modulation factors over 90%. Using replicated mirrors from MSFC and gratings made at MIT, we will construct a spectrometer that disperses to three laterally graded multilayer mirrors (LGMLs). The lateral grading changes the wavelength of the Bragg peak for 45 degree reflections linearly across the mirror, matching the dispersion of the spectrometer. By dividing the entrance aperture into six equal sectors, pairs of blazed gratings from opposite sectors are oriented to disperse to the same LGML. The position angles for the LGMLs are 120 degrees to each other, giving the three Stokes parameters needed to determine the source polarization. Our technological approach has significant promise for future missions that would operate in the soft X-ray band, with the potential to extend the bandpass to 1 keV. This sounding rocket program would provide a demonstration that a multilayer-based polarimetry approach can work, providing a basis for an orbital mission. Recent work focused on evaluating the use of sCMOS sensors for the detector system.

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