Systematic effects on a Compton polarimeter at the focus of an X-ray mirror

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This work is licensed under a Creative Commons Attribution 4.0 International License.

Authors

M Aoyagi, Osaka University
R G. Bose, Washington University
S Chun, Washington University
E Gau, Washington University
K Hu, Washington University
K Ishiwata, Osaka University
N K. Iyer, KTH Royal Institute of Technology
Fabian Kislat, University of New Hampshire, DurhamFollow
M Kiss, KTH Royal Institute of Technology
K Klepper, KTH Royal Institute of Technology
H Krawczynski, Washington University
L Lisalda, Washington University
Y Maeda, Institute of Space and Astronautical Science
F af Malmborg, KTH Royal Institute of Technology
H Matsumoto, Osaka University
A Miyamoto, Tokyo Metropolitan University
T Miyazawa, Okinawa Institute of Science and Technology Graduate University
M Pearce, KTH Royal Institute of Technology
B F. Rauch, Washington University
N Rodriguez Cavero, Washington University
S Spooner, University of New Hampshire, Durham
H Takahashi, University of New Hampshire, Durham
Y Uchida, Tokyo University of Science
A T. West, Washington University
K Wimalasena, University of New Hampshire, Durham
M. Yoshimoto, Osaka University

Abstract

XL-Calibur is a balloon-borne Compton polarimeter for X-rays in the $\sim$15-80 keV range. Using an X-ray mirror with a 12 m focal length for collecting photons onto a beryllium scattering rod surrounded by CZT detectors, a minimum-detectable polarization as low as $\sim$3% is expected during a 24-hour on-target observation of a 1 Crab source at 45$^{\circ}$ elevation. Systematic effects alter the reconstructed polarization as the mirror focal spot moves across the beryllium scatterer, due to pointing offsets, mechanical misalignment or deformation of the carbon-fiber truss supporting the mirror and the polarimeter. Unaddressed, this can give rise to a spurious polarization signal for an unpolarized flux, or a change in reconstructed polarization fraction and angle for a polarized flux. Using bench-marked Monte-Carlo simulations and an accurate mirror point-spread function characterized at synchrotron beam-lines, systematic effects are quantified, and mitigation strategies discussed. By recalculating the scattering site for a shifted beam, systematic errors can be reduced from several tens of percent to the few-percent level for any shift within the scattering element. The treatment of these systematic effects will be important for any polarimetric instrument where a focused X-ray beam is impinging on a scattering element surrounded by counting detectors.

Department

Physics

Publication Date

2-20-2024

Journal Title

Astroparticle Physics

Publisher

Elsevier BV

Digital Object Identifier (DOI)

https://dx.doi.org/10.1016/j.astropartphys.2024.102944

Document Type

Article

Recommended Citation

M. Aoyagi, R.G. Bose, S. Chun, E. Gau, K. Hu, K. Ishiwata, N.K. Iyer, F. Kislat, M. Kiss, K. Klepper, H. Krawczynski, L. Lisalda, Y. Maeda, F. af Malmborg, H. Matsumoto, A. Miyamoto, T. Miyazawa, M. Pearce, B.F. Rauch, N. Rodriguez Cavero, S. Spooner, H. Takahashi, Y. Uchida, A.T. West, K. Wimalasena, M. Yoshimoto, Systematic effects on a Compton polarimeter at the focus of an X-ray mirror, Astroparticle Physics, Volume 158, 2024, 102944, ISSN 0927-6505, https://doi.org/10.1016/j.astropartphys.2024.102944.

Rights

© 2024 The Author(s). Published by Elsevier B.V.

Comments

This is an open access article published by Elsevier BV in Astroparticle Physics in 2024, available online: https://dx.doi.org/10.1016/j.astropartphys.2024.102944