2020-11_OISTER-WS-IXPE.ppt

X-ray Polarimetry Mission
IXPE(X線偏光観測衛星測IXPE)
November 11, 2020 @ 11th OISTER WS
Tsunefumi Mizuno (Hiroshima Univ.)
on behalf of the IXPE team

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Polarization (1)• Electrons + magnetic field
Magnetic
produce synchrotron Electron
field line (B)pathradiation• Unique probe to B (andaccelerated electrons)
photon• High polarization degree is polarization vector ⊥ B direction
𝒑𝒑+𝟏𝟏~𝟎𝟎.
𝟕𝟕)
expected (𝛱𝛱𝐦𝐦𝐦𝐦𝐦𝐦 =⁄𝒑𝒑+𝟕𝟕 𝟑𝟑• X-ray polarimetry can probe
B-field configuration aroundfreshly-accelerated electrons
𝟑𝟑𝜸𝜸𝟐𝟐 𝒆𝒆𝒆𝒆)(𝒉𝒉𝝎𝝎𝐩𝐩 ~𝟎𝟎. 𝟐𝟐𝟐𝟐
𝟐𝟐𝒎𝒎𝐞𝐞 𝒄𝒄

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Polarization (2)• Reflected photons are𝟏𝟏− cos 𝜽𝜽 𝟐𝟐polarized (𝜫𝜫 =)𝟐𝟐𝟏𝟏+ cos 𝜽𝜽• Unique probe to geometry ofcompact objects (lightsource and accretion disk)
not accessible by imaging• Also probes relativistic effectaround a black hole (BH)
• We can investigate disk &space-time geometry using
X-ray polarimetry

𝜽𝜽

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3C279 (Abdo +10, Nature 463, 919)
• Optical polarization aided with MW obs.
revealed (possible) helical magnetic field
associated with flare

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Imaging-Spectro-Polarimetry• Polarization is powerful probe to magnetic
field and source geometry– It improves our understanding of objects– Multiwavelength observation is important• X-ray polarimetry has been unexplored but is
key in high-energy astrophysics– Probes B-field around freshly-accelerated
electrons, geometry (disk & space-time) in thevicinity of BH• IXPE is the first dedicated X-ray imagingpolarimetry observatory
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X-ray/γ-ray Polarimetry• Only a few measurements in X-ray/γ-ray– Integral (Crab, Cyg X-1) in >100 keV– PoGO+ (Crab, Cyg X-1) in 20-160 keV– ASTROSAT (Crab, Cyg X-1) in > 100 keV– Hitomi SGD (Crab) in >60 keV• In soft X-ray (<10 keV), Crab Nebula is firstand only positive detection
OSO-8 satellite (1975-)

Weisskopf 18• Graphite Bragg crystal• Crab nebula (w/o pulsar):
𝑷𝑷𝑷𝑷 = 𝟏𝟏𝟏𝟏% ± 𝟏𝟏𝟏
𝑷𝑷𝑷𝑷 = 𝟏𝟏𝟏𝟏𝟏𝟏° ± 𝟐𝟐°

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IXPE Mission• With IXPE, we can study several 10s sourcesin soft X-ray polarization• NASA SMEX mission, launch in late 2021, baseline
duration 2 years• Japanese group provides key devices of theinstruments• Data are made public after validation

2-8 keV
FOV=12.9’ x 12.9’, HPD=25”
3×(mirror + detector)

Weisskopf 18
7/27

Team and Mission Description• Bilateral collaboration between NASA/MSFC
and Italian Space Agency (ASI)• Japanese group provides key devices; mirror
thermal shield and Gas electron multiplier

PI: Martin Weisskopf(NASA Marshall Space Flight Center)• Launch on a Falcon 9 from KSC• 600-km circular orbit at 0.1 deg
inclination• 2 year baseline mission, 1 year
optional extension with GO program• Point-and-state at pre-selectedtarget• Science Operation Center (SOC) atMSFC• Mission Operation Center (MOC) at
CU/LASP• Malindi ground station (SingaporeBackup)
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Operation and Data Archive/Release• 2+1 years mission, point-and-state at preselected target• Observing plans (OPs) for 1st and 2nd years aredefined by the IXPE team• If mission is extended, OP will be GO-based• MOC generates OP every week (TOO possible)• Data are archived by NASA’s HEASARC andreleased with the following timing:• (First three months) 1 months after completion ofthe observation (data for 90% of the scheduled
observing time are received by MOC)
• (After that) 1 week after the completion of the obs.
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Ground Station Summary

MOC
LASP

SOC
HEASARC
GSFC
MSFC
Science Data

Orbit
Insertion

Arrays
DeployPayloadDeploys

TDRSS

S-band Uplink• 2 kbps CMDs
Data
Commands/Telemetry/Event Logs/Parameter
Uploads

Launch(late 2021)

S-band Downlink•
2 Mbps Science and TLM•
32 kbps Contingency
Ops•
1 kbps to TDRSSSingaporeGround Station

MalindiGround Station

10/27

IXPE Observatory (Deployed)• 2-8 keV, 3 Detector Units (DUs) and Mirror
Module Assemblies (MMAs)• Japanese group provides key devices (GEMfor DU and thermal shield for MMA)
Project Status:
2017/1 accepted for NASA SMEX
2020/3E production of TS completed,shipped to US
2020/3-5, NASA/MSFC almost
shutdown due to COVID-19
2020/6 env. test of MMA completed
2021/E launch

11/27

Detector Instrument• Three Detector Units (DUs) and singleDetector Service Unit (on underside of deck)constitute the instrumentFOV=12.9’ x 12.9’ (10’ overlapping)

Detector
Detecto Units(rotatedr Units by 120 deg
with each other)

12/27

Pol. Measurement Principle• Direction of photoelectron is parallel (onaverage) to incident X-ray polarization
𝒅𝒅𝝈𝝈
𝐬𝐬𝐬𝐬𝐬𝐬 𝜽𝜽 𝐜𝐜𝐜𝐜𝐜𝐜 𝝋𝝋 𝟐𝟐∝𝒅𝒅𝜴𝜴
𝟏𝟏 − 𝜷𝜷 𝐜𝐜𝐜𝐜𝐜𝐜 𝜽𝜽 𝟒𝟒pol. direction

GEM(RIKEN)Electron track image

𝝁𝝁𝟏𝟏𝟏𝟏𝟏𝟏 ~𝟎𝟎. 𝟓𝟓
achieved

Gas pixel detector (GPD)

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Gas Electron Multiplier (GEM)
110,000 holes (50 µm pitch)with no defect

15 mm(CERN+09)

460-480 V
Amplified by 300-500

Screening and test at RIKEN

14/27

EM X-ray Polarimeter
Acquisition on 8October

1 yr

Unpolarized source @5.9 keVLong term stability and uniformity
checked with Fe-55 source
Energy resolution <17%, integrated
over the entire detector surface (aftergain equalization)

15/27

Mirror Module Assembly
Mirror shells (24)

EM MMA

Thermal Shields(Nagoya)
Housing

Front Spider

HPD < 25"
Outer Housing

3 MMAs, 210 cm2(2.3 keV) each• 3 modules, each uses a single rigidspider to support 24 shells• light weight housing for thermal control
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Mirror Thermal Shieldpolyimide film
Al frame
300 mmstainless mesh• 1.4 µm Polyimide film, coated with 50 nm alminium• Supported on 97.5% transparent stainless-steel mesh (onAl frame)• Transmission factor 90% at 2 keV• Similar to shields flown on Hitomi
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IXPE Scientific Capability• Time to reach minimum detectable polarization(MDP) ~100 times shorter than that of OSO-8• Various classes of sources accessible
Targets under discussion(a few 10s pre-selectedtargets + transients)
Employ stokes-param.
based analysis

Crab Nebula

18/27(event-by event) Stokes Param. based
Analysis(Slide by S. Gunji for JPS meeting 2019/Mar)

Stokes parameter is additive => flexible binning in sky coordinate
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Case 1: Cen A• X-ray imaging polarimetry for the first time
• Investigate B-field configuration of jet for Cen A– Axial vs. transverse, how B-field orientation evolves
along the jet– ULX contamination excluded

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Case 2: Crab Nebula• X-ray imaging polarimetry for the first time
• Crab Nebula: past measurements (integrated)– OSO-8: 2.6&5.2 keV, PD=19%, PA=156 deg (Weisscopf +78)
– PoGO+: >20 keV, PD=19%, PA=124 deg (Chauvin +17)

• We want to distinguish (possibly) different
polarization in inner/outer nebulae by IXPE

124 deg

156 deg

Input polarization model:
PD=19% (uniform)
PA=124 deg (inner), 156 deg (outer)
30 ks obs, apply phase-cut (60% remained)
to eliminate pulsar contribution
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Case 2: Crab Nebula (Contd.)• Can distinguish inner- and outer-nebulapolarizations with imaging capability of IXPE
• By applying phase-cut, we can recover thechange of PD/PA
by R. Yamamoto (Hiroshima)Pol. degree(2-2.8 keV)

Pol. angle(2-2.8 keV)(Reg1+2 covers the X-ray torus)

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Case 3: Tycho SNR• Turbulent B filed expected at SNR shock. Evolutionof B turbulence is under debate• Radio observation generally reveals radial/tangential
field for young/old SNRs
• X-ray probes thin layer immediately behind theshock
Expected pol. directions for(A) anisotropic turbulence
produced by shock compression(B) turbulence produced byanisotropic cascade(Bykov +20)
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Case 3: Tycho SNR (Contd.)• X-ray probes B-filed configuration behind the shock
Tycho SNR, pol properties by numerical simulation,
1 MS obs. with IXPE
(A) anisotropic turbulence by shock compression(B) turbulence produced by anisotropic cascadeCan distinguish A (top) and B (bottom)
PD

PA

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Case 4: GRS 1915+105• Spectro-polarimetry probes space-time in thevicinity of BH– Photon scat. produces polarization; PD and PA
depend on disk inclination and optical depth– In general, relativistic effect results in energydependent depolarization and change of PA

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Case 4: GRS 1915+105 (Contd.)• Spectro-polarimetry probes space-time in thevicinity of BH– Photon scat. produces polarization; PD and PA
depend on disk inclination and optical depth– In general, relativistic effect results in energydependent depolarization and change of PA
GRS 1915+105 in soft state, IXPE 500 ks (Dovciak +08)

can discuss BH
spin w/ IXPE

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Summary• Polarization is powerful probe to magnetic
field and source geometry• IXPE will be launched in late 2021 and makethe spectro-imaging-polarimetry in– Japanese consortium contributes the mission inhardware and science– A few 10s sources are accessible for the first time
(AGN, PWN, SNR, BHB, etc.)– Coordinated (polarimetric) obs. would provide
vital information

Thank you for your Attention

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References
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Bykov et al. 2020, ApJ 899, 142
Chauvin et al. 2017, Scientific Report , 7816
Dovciak et al. 2008, MNRAS 391, 32
Novick 195, SSRv 18, 389
Kislat et al. 2015, Astroparticle Physics 68, 45
Vink & Zhou 2018, Galaxies 6, 46Weisskopf et al. 1978, ApJL 220, 117
Weisskopf et al. 2009, Proc. SPIE 7732, 77320E
Weisskopf 2018, Galaxies 6, 33

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Backup Slides

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Minimum Detectable Polarization• Modulation factor 𝝁𝝁𝟏𝟏𝟏𝟏𝟏𝟏 is relative amplitude ofmodulation curve for 100% polarized signal• Minimum detectable polarization (MDP99) is theminimum source polarization statisticallydistinguishable from 0% polarization
𝑵𝑵𝐦𝐦𝐦𝐦𝐦𝐦 + 𝑵𝑵𝐦𝐦𝐦𝐦𝐦𝐦
𝝁𝝁𝟏𝟏𝟏𝟏𝟏𝟏 =𝑵𝑵𝐦𝐦𝐦𝐦𝐦𝐦 − 𝑵𝑵𝐦𝐦𝐦𝐦𝐦𝐦

Nmax

Novick 75(Bragg crystal)

𝟒𝟒. 𝟐𝟐𝟐𝟐
𝟏𝟏 𝑹𝑹𝐒𝐒 + 𝑹𝑹𝐁𝐁
𝑴𝑴𝑴𝑴𝑴𝑴𝟗𝟗𝟗𝟗 =𝝁𝝁𝟏𝟏𝟏𝟏𝟏𝟏 𝑹𝑹𝐒𝐒 𝑻𝑻 𝑹𝑹𝐒𝐒

µ100=0.2-0.65 for IXPE
(Weisskopf 18)

Nmin
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Stokes Parameter based Analysis• We employ a Stokes Parameter basedanalysis to fully utilize imaging capability (cf.
Kislat +15, Vink +18)
• Unlike PD/PA, Stokes parameters are additive
and allow flexible binning in sky coordinate

Stokes Q (or U)
of each pixel

Average of4 pixels

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Stokes Param. based Analysis (Contd.)• Event-by-event Stokes parameters:
𝒊𝒊𝒌𝒌 = 𝟏𝟏, 𝒒𝒒𝒌𝒌 = 𝟐𝟐 𝐜𝐜𝐜𝐜𝐜𝐜 𝟐𝟐𝜽𝜽𝒌𝒌 , 𝒖𝒖𝒌𝒌 = 𝟐𝟐 𝐬𝐬𝐬𝐬𝐬𝐬 𝟐𝟐𝜽𝜽𝒌𝒌

• Stokes params. of entire data:

𝑰𝑰 = � 𝒊𝒊𝒌𝒌 = 𝑵𝑵 , 𝑸𝑸 = � 𝒒𝒒𝒌𝒌 , 𝑼𝑼 = � 𝒖𝒖𝒌𝒌

• Normalized parameters, PD and PA:
� = 𝑸𝑸⁄𝑰𝑰 , 𝑼𝑼
� = 𝑼𝑼⁄𝑰𝑰𝑸𝑸• Errors:

𝒑𝒑𝒓𝒓 =

𝟏𝟏𝝁𝝁𝟏𝟏𝟏𝟏𝟏𝟏

� 𝟐𝟐 + 𝑼𝑼
� 𝟐𝟐 , 𝜽𝜽 =𝑸𝑸

� 𝐞𝐞𝐞𝐞𝐞𝐞 =𝑸𝑸𝐞𝐞𝐞𝐞𝐞𝐞 𝟐𝟐 = � 𝒒𝒒𝒌𝒌 𝟐𝟐 = � 𝟐𝟐 𝐜𝐜𝐜𝐜𝐜𝐜 𝟐𝟐𝜽𝜽𝒌𝒌 𝟐𝟐 , 𝑸𝑸

𝟏𝟏
� ⁄𝑼𝑼
�
𝐭𝐭𝐭𝐭𝐭𝐭−𝟏𝟏 𝑸𝑸
𝟐𝟐𝑸𝑸𝐞𝐞𝐞𝐞𝐞𝐞 𝟐𝟐𝑰𝑰32/27

Polarization (1)• Electrons + magnetic fieldMagnetic
produce synchrotron Electronfield line (B)pathradiation• Unique probe to B (andaccelerated electrons)
photon• High polarization degree is polarization vector ⊥ B direction
𝒑𝒑+𝟏𝟏~𝟎𝟎.
𝟕𝟕)
expected (𝛱𝛱𝐦𝐦𝐦𝐦𝐦𝐦 =⁄𝒑𝒑+𝟕𝟕 𝟑𝟑

• Stokes parameters:𝜫𝜫 =𝑸𝑸𝟐𝟐 + 𝑼𝑼𝟐𝟐 + 𝑽𝑽𝟐𝟐
𝟏𝟏𝑼𝑼−𝟏𝟏, 𝝌𝝌 = 𝐭𝐭𝐭𝐭𝐭𝐭
𝑰𝑰𝟐𝟐𝑸𝑸

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Japanese Contribution to IXPE• Hardware contribution
 Mirror thermal shield (Nagoya Univ.) Gas electron multiplier (RIKEN)• Partially supported by JAXA’s small projectprogram• Japanese contributors
T. Tamagawa, T. Kitaguchi, T. Enoto (RIKEN),
I. Mitsuishi, Y. Tawara (Nagoya Univ.),
S. Gunji (Yamagata Univ.), T. Mizuno, Y. Fukazawa,
H. Takahashi (Hiroshima Univ.), K. Hayashida(Osaka Univ.), W. Iwakiri (Chuo Univ.) and students.
Names underlined are assigned as science collaborators.
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プロジェクト進捗• 2017年1月 NASA SMEX 採択• 2018年6月25-28日 mission PDR (基本設計審査) 通過• 2018年11月1日 KDP-C 通過• 2019年6月24-28日 mission CDR (詳細設計審査) 通過• 2020年3月末 FM 偏光計の較正試験完了、イタリアから米国へ輸送• 2020年3月末 FM サーマルシールド製作完了、米国納品• 2020年5月 Online Science Collaborator Meeting 開催• NASA/MSFC は3-5月の間、大半の実験停止• 2020年6月 望遠鏡単体試験＠MSFC 完了• FM 望遠鏡、FM偏光計 (3台分) 衛星への integration & test ＠BallAerospace• FM 望遠鏡+FM偏光計 (1台分) end-to-end 試験＠MSFC• 2021年後半 打ち上げ

天文学会＠筑波大（Mar. 18, 2020）

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