Polarization Leakage and the IXPE PSF
arxiv(2024)
摘要
By measuring photoelectron tracks, the gas pixel detectors of the Imaging
X-ray Polarimetry Explorer satellite provide estimates of the photon detection
location and its electric vector position angle (EVPA). However, imperfections
in reconstructing event positions blur the image and EVPA-position correlations
result in artificial polarized halos around bright sources. We introduce a new
model describing this "polarization leakage" and use it to recover the on-orbit
telescope point-spread functions, useful for faint source detection and image
reconstruction. These point spread functions are more accurate than previous
approximations or ground-calibrated products (Δχ^2≈ 3×
10^4 and 4 × 10^4 respectively for a bright 10^6-count source). We
also define an algorithm for polarization leakage correction substantially more
accurate than existing prescriptions (Δχ^2≈ 1× 10^3).
These corrections depend on the reconstruction method, and we supply
prescriptions for the mission-standard "Moments" methods as well as for "Neural
Net" event reconstruction. Finally, we present a method to isolate leakage
contributions to polarization observations of extended sources and show that an
accurate PSF allows the extraction of sub-PSF-scale polarization patterns.
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