age Yoneyama
- Koki Okazaki
- Shuntaro Ide
- Hirofumi Noda
- Hironori Matsumoto
- Hiroshi Tsunemi
- Hisamitsu Awaki
- Hiroshi Nakajima
bibliography:
- 'GMAX0505\_paper.bib'
title: 'X-ray imaging polarimetry with a 2.5-$\mathrm{\mu}$m pixel CMOS sensor for visible light at room temperature'
---

[**\***Kazunori Asakura, asakura$\_$k@ess.sci.osaka-u.ac.jp]{}

Introduction {#sec:intro}
============

Polarimetry is a powerful diagnostic tool to measure magnetic fields and scattering process of celestial objects. In fact, polarimetry has been widely employed for various targets and purposes in radio-to-ultraviolet astronomy. On the other hand, polarimetry in x-ray and $\gamma$-ray astronomy had long been an unexploited field after the first detection of polarization of the Crab Nebula with a sounding rocket instrument[@Novick1972] and succeeding satellite observations[@Weisskopf1978]. Polarimetry in hard x-ray and soft $\gamma$-ray astronomy has been markedly activated in these years, starting from the detection of polarization in the Crab Nebula with instruments on-board INTEGRAL[@Forot2008; @Dean2008]. Hard x-ray to soft $\gamma$-ray polarimetry of the Crab Nebula has succeeded in other instruments, e.g., the CZT Imager on ASTROSAT[@Vadawale2018], PoGO+[@Chauvin2017; @Chauvin2018], and the Soft Gamma-ray Detector on Hitomi[@Hitomi2018]. Polarization of Cyg X-1 has also been measured with some of these instruments. Gamma-ray bursts are also the targets of extensive observations of their polarization, with GAP on IKAROS[@Yonetoku2011], the CZT Imager on ASTROSAT[@Chattopadhyay2017], and POLAR on-board Tiangong-2[@Zhang2019]. The imaging x-ray polarimetry explorer (IXPE)[@Weisskopf2016], a small satellite mission dedicated to soft x-ray polarimetry, is scheduled to be launched in 2021.

Various polarimetry instruments have been developed in x-ray and $\gamma$-ray astronomy, as reviewed by Weisskopf et al.[@Weisskopf2010] They can be classified into three main categories by their working principle: Bragg reflec