1. Polarization Characteristic of Multi-layer Mirror for Hard X-ray Observation of Astrophysical Objects T. Mizuno 1, J. Katsuta 2, H. Yoshida 1, H. Takahashi 1, T. Iwahara 3, Y. Kano 3, N. Sasaki 3, Y. Ogasaka 3, T. Kamae 4, T. Takahashi 2, K. Hayashida 5 and K. Uesugi 6 1 Hiroshima University; 2 Japan Aerospace Exploration Agency; 3 Nagoya University; 4 Stanford Linear Accelerator Center; 5 Osaga University; 6 Japan Synchrotron Radiation Research Institute Abstract: Polarization measurements above 10 keV can provide crucial information about astrophysical objects. Despite of its importance, X-ray polarization has been measured only from Crab Nebula at 2.6 and 5.2 keV by OSO-8 (Weisskopf et al. 76 ). A hard X-ray mirror is expected to improve the sensitivity by more than an order of magnitude and provide a breakthrough in high-energy astrophysics. In order to examine a possible systematic errors in polarization measurement, we have measured the polarization dependence of the reflectance of multi-layer hard X- ray mirror to 30-keV X-rays at a medium-length beamline 20B2 in Spring-8 (Hyogo, Japan). The dependence was less than +-1%, ensuring that we are able to measure weak polarization down to a few % using hard X-ray optics. Modivation: Why polarimetory? polarimeter Multi-layer (Super) Mirror for pol. measurement: X-ray mirror X-ray X-ray condensing and imaging improve the sensitivity in spectroscopy and polarimetry in hard X-rays. Systematic errors in pol. measurement introduced by hard X-ray mirror  Reflectance of multi-layer mirror (weakly) depends on pol. vector R  ： Reflectance of  polarization (pol. vector is parallel to the mirror surface) R  : Reflectance of  polarization R  /R  =cos 2 2  where  is the beam incident angle  Artificial polarization of P’=(1-R  /R  )/(1+R  /R  )~(1-I 90 /I 0 )/2 will be introduced where I is the intensity of the reflected beam. (I 0 : pol. vector parallel to the mirror surface) 1 Incident angle  0.5 deg 1 deg 2 deg 0.1% 0.03% 0.5% Pol. angle dependence of the Intensity of reflected beam pol. vector azimuthal angle I/I 0 90 270deg180 Experiment: Precise measurement of the X-ray reflectance experimental setup Ion Chamber: beam intensity monitor precision motorized stages: rotation of mirror piece rotation angle  (30 degree step) Beam incident angle  ~0.5deg (0.001 deg step) fine tuning of the beam incident angle and mirror position Synchrotron emission: direction of B-field.  Pulsar wind nebular  Binary pulsar and rotation-powered pulsar  Jets in AGN and m-QSO Compton Scattering: orientation of the scatterer  Black-hole binaries (accretion disk geometry) Propagation in strong magnetic field: test of quantum electrodynamics, direction of B- field  Highly magnetized neutron star BHB,  -QSO Mirabel 2006 Crab nebula & pulsar by CXO Rot. Powered pulsar model Harding 2004 Aeff of NeXT HXT and Suzaku XRT Non-thermal process where high degree pol. is expected Effect on polarization measurement is predicted to be less than 1%, but needs to be confirmed experimentally. High stability is required careful examination of systematic errors (typical size of the reflected beam image) Long-term stability of NaI measured using a radioisotope ( 241 Am) 0.1% Systematic errors in Ion chamber and NaI scintillator (stability/uniformity) is <=0.3%. Pol. vector dependence of the reflectance was +-0.8%  Artificial polarization P’ = (1-I 90 /I 0 )/2 ~ 0.8%  We are able to use hard X-ray optics to measure polarization down to a few %. The dependence is larger than the theoretical prediction (~0.03%) and could affect the measurement of weak pol. measurement (such as the test of general relativity) if real.  Not due to the stability/uniformity of Ion chamber/NaI scintillator (<=0.3%).  Misalignment (beam position on mirror piece, shape of pin- hole collimator)? => under investigation 0.50 0.51 0.52 deg Reflectance Profile for  =0 deg Reflectance Profile for  =0 deg (expanded) Reflectance [a.u.] 0.51 0.512 deg Reflectance [a.u.] Beam incident angle  Reflectance of Multi-layer mirror as a function of pol. vector angle 相対反射率 1.6% 0 90 180 270 deg Relative reflectance  profile Performance of polarimeter with hard X-ray optics: Typical characteristics of polarimeter w/o mirror (e.g., PoGOLite, see poster by Madejski et al. #28.14) MF 100 ~0.3 Aeff=150-200 cm 2 in 25-80 keV (~15 c/s for Crab Nebula in 4g/cm 2 overburden) det. volume ~ 30000cm 3 BG~0.1 Crab (~1.8 c/s) Typical characteristics of polarimeter w/ mirror MF 100 ~0.6 Aeff~10 cm 2 in 25-70 keV (~1 c/s for Crab Nebula) det. volume ~100 cm 3 BG~0.005 c/s (proportional to det. volume) Summary: Polarimetry will bring a breakthrough in high- energy astrophysics  Pulsar model, structure of B-field and accretion disk, test of QED/general relativity, etc. Hard X-ray mirror will improve the sensitivity by more than an order of magnitude  Pol. measurement of weak objects (~10 mCrab) will be possible. We showed that the pol. dependence of reflectance of multi-layer mirror is less than 1%  The proof of the concept of “Polarimeter w/ Hard X-ray Optics” Polarization measurement above 10 keV is a very powerful tool to investigate source geometry and emission mechanism test on Nov. 28- Dec.1, 2007 0.5mm NaI scinti. + PMT: Reflectivity measurement We collimated the beam by using a pin-hole (0.5 mm diameter) to minimize the systematic errors. (image of the direct beam taken by CCD camera) Efficiency Scan profile Efficiency [a. u.] Reflected beam image shifts and rotates as we rotate the mirror. Position dependence of the efficiency of NaI is ~0.25% (1  ) 0 20 40 60 80 hr. Counts We measured reflectance peak of each  angle T=10ks/100ks/1Ms solid and dotted: w/ and w/o BG Polarimeter w/ mirror has better sensitivity for weak objects (<=10 mCrab) 0.25% Reflectance [a.u.] #28.16 MDP [%] Source Flux (Crab) 3  Minimum Detectable Plarizaton, Polarimeter w/o mirror 3  Minimum Detectable Plarization, Polarimeter w/ mirror