Speaker
Description
X-ray polarimetry is the most potent tool for capturing anisotropic geometries and physical processes that could not be resolved through mere spectroscopy alone. The launch of IXPE (Weisskopf et al. 2022) has opened a new door, enabling the detection of soft X-ray polarization with image reconstruction. The next essential endeavor is the imaging polarimetry in the hard X-ray band, where non-thermal radiation from celestial objects becomes more dominant and can yield a wealth of information.
We are developing a hard X-ray imaging polarimeter to be installed on a 6U CubeSat (referred to as cipher; Coded Imaging Polarimeter of High Energy Radiation, Odaka et al. 2020). This system employs a micro-pixel CMOS sensor for polarization detection via electron tracking. The imaging component employs a coded aperture, which imparts a distinct pattern onto the CMOS sensor. We conducted multiple beam tests using 100% polarized X-rays, validating the imaging polarimetry within the 10–30 keV energy range.
One of the conventional analysis methods for coded aperture imaging is the balanced correlation method (Fenimore et al. 1978), which has proven successful in reconstructing polarization maps in our system (Kasuga et al. 2021). However, this method induces significant uncertainties and noise levels in the resulting polarization maps. Consequently, we have developed a new algorithm that incorporates the Expectation-Maximization (EM) algorithm (Dempster et al. 1977) during the sky image reconstruction. The iterative calculation of maximum likelihood has enabled us to produce polarization maps with enhanced clarity, reduced noise levels, and a more accurate estimation of the polarization degree compared to the balanced correlation method. The artifacts in the decoded image were reduced by a factor of 0.12 from the balanced correlation method. In this presentation, we will show the latest analysis outcomes of imaging reconstruction using the EM algorithm, accompanied by a comparison to the classical method.
| Submission declaration | Original and unplublished |
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