Speaker
Description
X-ray polarimetry is expected to be an effective tool for revealing the geometrical and magnetic structures of celestial objects. With the launch of the Imaging X-ray Polarimetry Explorer (IXPE; Weisskopf et al. 2022) in 2021, polarimetric observations with high sensitivity in the $2$-$8~\mathrm{keV}$ energy band have begun. However, hard X-ray polarimetry in the $10$-$30~\mathrm{keV}$ energy band, where non-thermal radiation dominates and the number of photons is relatively abundant, is still challenging.
We are developing an imaging polarimeter using a micro-pixel complementary metal–oxide–semiconductor (CMOS) image sensor and a coded mask to realize polarimetry in the hard X-ray band of $10$-$30~\mathrm{keV}$. The polarization of the incident X-ray can be measured by tracing photoelectrons with a fine-pixel sensor. We call the project cipher (Coded Imaging Polarimetry of High Energy Radiation; Odaka et al. 2020) and measured the modulation factor of the CMOS image sensors with a pixel size of $2.5~\mathrm{\mu m}$.
In this study, we evaluate the polarization sensitivity of a CMOS image sensor with a pixel size of $1.5~\mathrm{\mu m}$ manufactured by Canon. In order to measure the modulation factor of the sensor, we irradiated the sensor with nearly perfectly polarized monochromatic X-rays at BL20B2 in SPring-8, a synchrotron radiation facility in Japan. The obtained modulation factors of the sensor were $8.8\%$ at $10~\mathrm{keV}$ and $13.5\%$ at $16~\mathrm{keV}$, which were higher than that of the sensor with a pixel size of $2.5~\mathrm{\mu m}$ measured by Odaka et al. (2020). These results show that the modulation factor can be improved by using a finer-pixel sensor. We also estimate the detection efficiency of the sensor. We will discuss the polarization sensitivity of fine-pixel sensors by comparing the results of the experiments and simulations.
| Submission declaration | Original and unplublished |
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