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Proceedings Paper

REDSoX: Monte-Carlo ray-tracing for a soft x-ray spectroscopy polarimeter
Author(s): Hans M. Günther; Mark Egan; Ralf K. Heilmann; Sarah N. T. Heine; Tim Hellickson; Jason Frost; Herman L. Marshall; Norbert S. Schulz; Adam Theriault-Shay
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Paper Abstract

X-ray polarimetry offers a new window into the high-energy universe, yet there has been no instrument so far that could measure the polarization of soft X-rays (about 17-80 Å) from astrophysical sources. The Rocket Experiment Demonstration of a Soft X-ray Polarimeter (REDSoX Polarimeter) is a proposed sounding rocket experiment that uses a focusing optic and splits the beam into three channels. Each channel has a set of criticalangle transmission (CAT) gratings that disperse the x-rays onto a laterally graded multilayer (LGML) mirror, which preferentially reflects photons with a specific polarization angle. The three channels are oriented at 120 deg to each other and thus measure the three Stokes parameters: I, Q, and U. The period of the LGML changes with position. The main design challenge is to arrange the gratings so that they disperse the spectrum in such a way that all rays are dispersed onto the position on the multi-layer mirror where they satisfy the local Bragg condition despite arriving on the mirror at different angles due to the converging beam from the focusing optics. We present a polarimeteric Monte-Carlo ray-trace of this design to assess non-ideal effects from e.g. mirror scattering or the finite size of the grating facets. With mirror properties both simulated and measured in the lab for LGML mirrors of 80-200 layers we show that the reflectivity and the width of the Bragg-peak are sufficient to make this design work when non-ideal effects are included in the simulation. Our simulations give us an effective area curve, the modulation factor and the figure of merit for the REDSoX polarimeter. As an example, we simulate an observation of Mk 421 and show that we could easily detect a 20% linear polarization.

Paper Details

Date Published: 29 August 2017
PDF: 13 pages
Proc. SPIE 10399, Optics for EUV, X-Ray, and Gamma-Ray Astronomy VIII, 1039917 (29 August 2017); doi: 10.1117/12.2273772
Show Author Affiliations
Hans M. Günther, MIT Kavli Institute for Astrophysics and Space Research (United States)
Mark Egan, MIT Kavli Institute for Astrophysics and Space Research (United States)
Ralf K. Heilmann, MIT Kavli Institute for Astrophysics and Space Research (United States)
Sarah N. T. Heine, MIT Kavli Institute for Astrophysics and Space Research (United States)
Tim Hellickson, MIT Kavli Institute for Astrophysics and Space Research (United States)
Jason Frost, Stanford Univ. (United States)
MIT Kavli Institute for Astrophysics and Space Research (United States)
Herman L. Marshall, MIT Kavli Institute for Astrophysics and Space Research (United States)
Norbert S. Schulz, MIT Kavli Institute for Astrophysics and Space Research (United States)
Adam Theriault-Shay, MIT Kavli Institute for Astrophysics and Space Research (United States)


Published in SPIE Proceedings Vol. 10399:
Optics for EUV, X-Ray, and Gamma-Ray Astronomy VIII
Stephen L. O'Dell; Giovanni Pareschi, Editor(s)

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