Japanese X-ray Polarization Activities
Hiromitsu Takahashi (Hiroshima U.)
hirotaka@astro.hiroshima-u.ac.jp<10 keV: IXPE (Imaging X-ray Polarimetry Explorer)
GEM: RIKEN (Tamagawa-san)Thermal shield (mirror) : Nagoya U. (Mitsuishi-san)

10s keV: PoGO+, XL-Calibur balloons (Next slides)
100s keV:Hitomi (ASTRO-H)/SGD: Crab detection (2018 PASJ 70, 113)
Analysis software in Heasoft/ftool

SMILE balloon
Electron-tracking Compton camera with micro-pixel chamber: Kyoto U.
(Takada-san)
MeV: GRAIN balloon
Fine image with emulsion films: Kobe U., Nagoya U.
(Takahashi-san, Rokujo-san)All researchers need more launch opportunities and want better detection/analysis methods.
1I hope we can start any cooperation at any levels.

Recent balloon-borne hard X-ray polarimeters
PoGOLite/PoGO+ PI: Pearce(2011,2013,2016)
Sweden + Japan

X-Calibur/XL-Calibur PI: Krawczynski(2018,2022,…)

Joined from 2018

US + Japan + Sweden
Mirror (from Japan)

Collimator
Polarimeter

Focal Length8－12 mPolarimeter

1m

Collimator type (20-180 keV)
Large effective area
but with high background(Chauvin et al. 2017,2018 etc.)

Focusing type (20-80 keV)
Low background with small detector(Abarr et al. 2020,2021 etc.)

X-Calibur in 2018 (~2 tons)3

X(L)-Calibur Polarimeter

20-80 keV

- Compton scattering is used to measure polarization angle
Focus with hard X-ray mirror => Detector is compact and low background
Scatter: Be (passive), Absorber CZT (256 pix x 4 sides), CsI (next BGO) active shield
1 CZT (64 pix) at bottom as an imager- Detector rotates (360 deg/20 s) to cancel systematic errors.
Focal length: 8-12 m

Detector size: ~3x8cm

2018: InFOCuS mirror (NASA+Japan)>2022: FFAST mirror (Japan)

4

Next: XL-Calibur flights in 2022, 2023, …
（Abarr et al. 2021）

Updates:(1) Use larger mirror(developed for FFAST mission)⇒ Signal increase(2) Thinner CZT (0.8-mm thickness)(3) Anticoincidence shield
Faster circuit (less deadtime)
BGO scintillator⇒ Background decrease⇒ >10 times better S/N ratio
than the previous X-Calibur.
(4) Sun sensor and another star tracker
for pointing Crab (close to Sun).
5

Estimated sensitivity of XL-Calibur (15-80 keV)2022: Arctic (Sweden- Canada), ~1 week flight
Crab (calibration), Cyg X-1 (BHB) => Accretion corona geometry

2023: Antarctica, ~1 month flight
Vela X-1, GX 301-2 (HMXBs) => Emission mechanism (Fan/Pencil beam?)
Simultaneous observations with IXPE and XPoSat are very interesting.

Cyg X-1 (Black-hole binary)

GX 301-2 (HMXB)(700 mCrab)

Low/hard state: can detect a few% polarization
High/soft state: upper limit <~5%If flux is in 2018 level,polarization can be detected significantly.

6Japanese X-ray Polarization Activities
Hiromitsu Takahashi (Hiroshima U.)
hirotaka@astro.hiroshima-u.ac.jp<10 keV: IXPE (Imaging X-ray Polarimetry Explorer)
GEM: RIKEN (Tamagawa-san)Thermal shield (mirror) : Nagoya U. (Mitsuishi-san)

10s keV: PoGO+, XL-Calibur balloons (Next slides)
100s keV:
Hitomi (ASTRO-H)/SGD: Crab detection (2018 PASJ 70, 113)
Analysis software in Heasoft/ftool

SMILE balloon
Electron-tracking Compton camera with micro-pixel chamber: Kyoto U.
(Takada-san)
MeV: GRAIN balloon
Fine image with emulsion films: Kobe U., Nagoya U.
(Takahashi-san, Rokujo-san)All researchers need more launch opportunities and want better detection/analysis methods.
7I hope we can start any cooperation at any levels.