X- ray Polarimetry Satellite GEMS and beyond

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1 ithes Mini-workshop on "Strong-Field Physics X- ray Polarimetry Satellite GEMS and beyond RIKEN Nishina Center Toru Tamagawa

2 Strong- field Physics(May. 29, 2014) 2 Introduc8on X-ray polarimetry is the best way to observe the strong magnetic and gravitational field in universe. X-ray polarimetry is technically very difficult to realize but we did develop very sensitive X-ray polarimeter. NASA s GEMS (Gravity and Extreme Magnetism Small Explorer) is the first dedicated mission for sensitive X-ray polarimetry. Project is stopped due to cost overrun, but we propose it again in 2014.

3 Strong- field Physics(May. 29, 2014) 3 Outline 1. X- ray Polarimetry 2. GEMS Project 3. Neutron stars (Strong magne8c field) 4. Black holes (Strong gravita8onal field) 5. Summary

4 1.1 Open a New Field in Astrophysics Strong- field Physics(May. 29, 2014) 4 Imaging Spectroscopy Suzaku Timing Chandra CXC/NASA JAXA MAXI (Hayato+2010) NASA/JAXA Tycho s SNR CXC/NASA Tycho s SNR Polariza6on l New dimension l Final fron8er in X- ray Astrophysics Polarimetry is technically easy in radio and op8cal, but not in X- ray/gamma- ray. We should know electric vector photon- by- photon. (maxi web より )

1.2 Origin of Polarized X- rays All elementary processes are related to

strong magnetic field radiate with polarization perpendicular to B.

creates 100% polarized X-rays source Jet from BH P~100% θ // surface BH

5 1.2 Origin of Polarized X- rays All elementary processes are related to polarization l Synchrotron emission Ø P~70% θ B electron B Electrons in strong magnetic field radiate with polarization perpendicular to B. Particle acceleration at shock synchrotron NASA l Scattering Scattering creates 100% polarized X-rays source Jet from BH P~100% θ // surface BH accretion disk synchrotron Strong- ﬁeld Physics May. 29, 2014 Thomson scat. 5

6 1.3 Propaga8on of photons in B field Strong- field Physics(May. 29, 2014) 6 E << E cyc =11.6B 12 kev O- mode B no restric8on k σ/σ T Cross-section O-mode Cyclotron 11.6 B 12 kev X- mode B k Frequency mo8on is restricted by magne8c field Cross-section is modified from its original Thomson scattering. This is why we expect highly polarized X-ray from neutron stars.

7 1.4 Magne8zed Plasma Strong- field Physics(May. 29, 2014) 7 Accretion Powered Pulsar Hercules X-1 (dal Fiume+1998) B~10 12 G X-ray from accretion column Flux X-rays from accretion column Cyclotron Abs. Highly polarized X-rays (X-mode photons) are expected. Magnetized plasma = good polarizer Energy (kev) We can extract information about geometry, magnetic field structure etc. combining with other observations.

$(near BH) l Vacuum birefringence QED vacuum with strong B B Itakura-san Refractive indices are different in different direction. l Primakoff process Connection to axion. Polarized to the B direction.$

8 1.5 Photon Propaga8on l Light-bending (GR effect) Light-bending rotates the direction of polarization. This leads decrease of polarization degree. (near BH) l Vacuum birefringence QED vacuum with strong B B Itakura-san Refractive indices are different in different direction. l Primakoff process Connection to axion. Polarized to the B direction. B 0 How can we observe this effect in the universe? Strong- field Physics(May. 29, 2014) 8

9 1.6 What we can know? Strong- field Physics(May. 29, 2014) 9 1. Small structure which we cannot image with current technology Origin of X- ray emission near neutron stars Geometry of accre8on disk near black holes Par8cle accelera8on at the shell of Supernova remnants 2. Photon propagation in strong field photon propaga8on in magne8zed plasma and QED vacuum(vacuum birefringence) near neutron stars. photon propaga8on in strong gravita8onal field near black holes. GR effects, Light- bending, Spin of BHs.

10 1.7 History of X- ray Polarimetry Strong- field Physics(May. 29, 2014) 10 Crab Nebura observations 1. Sounding Rocket (Norvick+1972) 2. OSO-8 (Weisskopf +1976, 78) ~ 30 yrs blank 3. PHENEX(Gunji+2007) 4. INTEGRAL(Dean+2008) Why only Crab? Very bright object Highly polarized by Synchrotron X-ray polarimetry astrophysics is before dawn. (C) NASA/CXO OSO-8 (Weisskopf+1978) P=19.2±1.0%@2.6 kev θ=156.4±0.4deg INTEGRAL (Dean+2008) P=46±10%@0.1-1MeV θ=123±11deg (rot axis = 124.0±0.1deg)

11 Strong- field Physics(May. 29, 2014) 11 Outline 1. X- ray Polarimetry 2. GEMS Project 3. Neutron stars (Strong magne8c field) 4. Black holes (Strong gravita8onal field) 5. Summary

12 2.1 GEMS mission overview Strong- field Physics(May. 29, 2014) 12 X- ray grazing mirrors The Gravity and Extreme Magne6sm Explorer (GEMS) 4.5 m detectors at focus Selected by NASA in 2009 for launch in 2014 (NASA Small Explorer Mission). GEM- TPC polarimeters at the focus of X- ray op8cs, on the rota8ng space craf (0.1 rpm). Energy Band: 2-10 kev Mission Life8me > 9 months (goal 2 years) Low Earth Orbit 565 km, inclina8on 28.5 deg. Project non- confirmed in 2012 due to cost overrun, but we will propose the mission again in 2014

2.2 How to measure X- ray polariza8on X-ray E φ differen8al cross sec8on cos 2 φ quantum efficiency can be ε ~ 1 Analyzing power µ=1 (intrinsic) but µ<1 (in reality) rela8ve count Auger electron

13 2.2 How to measure X- ray polariza8on X-ray E φ differen8al cross sec8on cos 2 φ quantum efficiency can be ε ~ 1 Analyzing power µ=1 (intrinsic) but µ<1 (in reality) rela8ve count Auger electron Photoelectron A gas detector is essen8al to obtain a longer photoelectron track. A micro paqern gas detector is also essen8al to reconstruct the track. µ = N max N min N max + N min Figure of merit photo- e azimuthal angle (rad) Strong- field Physics(May. 29, 2014) 13

14 2.3 Design of GEM- TPC polarimeter Strong- field Physics(May. 29, 2014) 14 GEM- TPC as a photoelectron track imager (Black+2007) 50 nsec 120 microns A 8me- projec8on technique creates pixel images from a 1D readout. l Pure DME (C 2 H 6 O), 190 Torr to obtain longer photoelectron tracks l Longer (>30cm) effec8ve volume along the op8cal- axis for good detec8on efficiency l Slow drif velocity of DME = spacing of strips (0.25cm/us * 20 MHz = 120 micron)

15 2.4 GEM- TPC Polarimeter Strong- field Physics(May. 29, 2014) 15 Detector Assembly: Field- cage and DriH Planes 32 cm veto region Effec8ve Volume 2cm x 2cm x 7.8 cm (one unit)

2.5 Readout strip and GEM foils Readout strip and ASIC

8 cm long) l veto region in both side l connec8ng to APV25

16 2.5 Readout strip and GEM foils Readout strip and ASIC (APV25) GEM foil 30 cm 3cm 7.8 cm APV25 Readout strip l 128 strips (pitch 120, width 60 micron, 7.8 cm long) l veto region in both side l connec8ng to APV25 (20 MHz clock) GEM foil l LCP- GEM l 140 micron pitch, 70 micron hole l 100 micron thick GEM- Strip alignment 120 micron Strong- field Physics(May. 29, 2014) 16

2.6 Polarimeter Sensi8vity Strong- field Physics(May. 29, 2014) 17 minimum detectable polarization MDP = 4.

17 2.6 Polarimeter Sensi8vity Strong- field Physics(May. 29, 2014) 17 minimum detectable polarization MDP = µ r r + b T µ=modulation factor r=signal count rate b=background rate T=duration Magnetars Targets with known fluxes and polariza8on es8mates GEMS sensitivity. Black holes Neutron stars Supernova remnants

Strong- field Physics(May. 29, 2014) 18 2.

semi-flight polarimeter: demonstrated required sensitivity Schedule 2014/12

18 Strong- field Physics(May. 29, 2014) Readiness to the Flight Flight Mirror: already fabricated. semi-flight polarimeter: demonstrated required sensitivity Schedule 2014/12 NASA SMEX proposal 2015/06 1 st step selection 2016/08 2 nd step selection 2019 or 2020 launch We are almost ready to flight!

19 Strong- field Physics(May. 29, 2014) 19 Outline 1. X- ray Polarimetry 2. GEMS Project 3. Neutron stars (Strong magne8c field) 4. Black holes (Strong gravita8onal field) 5. Summary

20 3.1 Magne8c Field of Pulsars Strong- field Physics(May. 29, 2014) 20 P-dot P plot of pulsars magnetic field estimation Some neutron stars have very strong magnetic field, B>Bcr Landau level separation mass of electron Enoto 2010 We can observe QED effects around those high magnetic field.

21 3.2 Vacuum Polariza8on Strong- field Physics(May. 29, 2014) 21 Hot Spot observer X-ray emitted at the hotspot goes through highly magnetized plasma (neutron star atmosphere). Dielectric tensor of magnetized plasma with vacuum polarization (Lai+2009) (Mereghetti+2008) (Meszaros&Ventura, 1978 etc.) Density gradient exists in the atmosphere of neutron stars. At some point, dielectric tensors of plasma and vacuum are canceled each other. Δε plasma + Δε vac 0

22 Strong- field Physics(May. 29, 2014) Vacuum Resonance If the adiabatic condition is satisfied, G, 5keV, 45deg Vacuum resonance (Lai & Ho 2002, 2003) At the vacuum resonance, X-mode and O- mode are similar each other. X-mode and O-mode are coupled if the adiabatic condition is satisfied. Bussard+1986

23 3.4 B=10 13 G Strong- field Physics(May. 29, 2014) 23 (Lai, 2009) vanadelsberg&lai 2006 decoupling clear evidence of vacuum resonance Detection of Vacuum Resonance is a science goal of GEMS First observed results of QED vacuum in the universe.

24 3.5 B=5x10 14 G (> Bcr) Strong- field Physics(May. 29, 2014) 24 (Lai, 2009) vanadelsberg&lai 2006 plane of polarization at different energy coincide.

25 3.6 Hard Component Strong- field Physics(May. 29, 2014) 25 (Enoto, 2010) (Mereghetti+2008) BB hard component Hard component exist in many magnetars. But the origin is not known. Curvature radiation? Photon splitting? How much polarized of the hard component? What does the polarization degree means?

26 Strong- field Physics(May. 29, 2014) 26 Outline 1. X- ray Polarimetry 2. GEMS Project 3. Neutron stars (Strong magne8c field) 4. Black holes (Strong gravita8onal field) 5. Summary

$polarized fraction is 0-12 % depending on inclination (Chandrasekhar 1960) The polarization direction is parallel to the disk surface.$

27 4.1 Polarized X- ray from BH In an optically thick accretion disk, the atmosphere is dominated by Compton scattering (100% polarized perpendicular to the scattering plane for 90deg scattering) The polarized fraction is 0-12 % depending on inclination (Chandrasekhar 1960) The polarization direction is parallel to the disk surface. side- on face- on disk interior observer polariza8on (%) Escaping radia8on polarized parallel to surface cos(i) Strong- field Physics(May. 29, 2014) 27

28 4.2 GR effect and scaqering Strong- field Physics(May. 29, 2014) 28/10 Propaga8on to the observer is affected by Special rela8vis8c effects (Doppler shif, aberra8on, beaming) and general rela8vis8c effects (redshif, light- bending) a/m=0.998 i=70 o Returning radia8on, which scaqers 90deg into our line of sight, has a significant effect on polariza8on (Shuniqman+2010)

29 4.3 blackhole polariza8on behavior Strong- field Physics(May. 29, 2014) 29 (Schniqman and Krolik 2009)

Spin- off of X- ray Polarimeter Strong- field Physics(May.

system 2-10 kev MDP ~ 1% δθ < 5 deg 30 cm 2014/10 Performance

30 Spin- off of X- ray Polarimeter Strong- field Physics(May. 29, 2014) 30 Built our own polarimeter at RIKEN. NO export (ITAR) regulation. Easily modify for any applications Very compact detector system 2-10 kev MDP ~ 1% δθ < 5 deg 30 cm 2014/10 Performance Test at SPring /12 Atomic physics experiment at HIMAC (with Azuma-san) 2015 SPring-8 or XFEL plasma physics etc.

X-ray polarimetry and new prospects in high-energy astrophysics

X-ray polarimetry and new prospects in high-energy astrophysics Carmelo Sgrò INFN Pisa carmelo.sgro@pi.infn.it Frascati, March 31, 2016 A new exploration window: X-Ray polarimetry Spectroscopy, imaging