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.
@article{arxiv.2302.00346,
title = {Polarisation Leakage due to Errors in Track Reconstruction in Gas Pixel Detectors},
author = {N. Bucciantini and N. Di Lalla and R. W. R. Romani and S. Silvestri and M. Negro and L. Baldini and A. F. Tennant and A. Manfreda},
journal= {arXiv preprint arXiv:2302.00346},
year = {2023}
}