Polarisation Leakage due to Errors in Track Reconstruction in Gas Pixel Detectors
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Date
2023-02-01
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
X-ray polarimetry, based on Gas Pixel Detectors (GPDs), have reached a high level of maturity with the Imaging X-ray Polarimeter Explorer (IXPE) leading to the first ever spatially resolved polarimetric measures. However, being this a new technique, a few
unexpected effect have emerged during in flight operations. In particular it was almost immediately found that on-board unpolarized
calibration sources were showing radially polarized halos. The origin of this features was recognized in a correlation between the error
in reconstructing the absorption point of the X-ray photon and the direction of its electric field vector. Here we present and discuss in
detail this effect, showing that it is possible to provide a simple and robust mathematical formalism to handle it. We further show its
role and relevance for the recent IXPE measures, and for the use of GPD-based techniques in general, and illustrate how to model it
in the study of extended sources.