気球搭載硬X線偏光計PoGOLiteの波形弁別部の評価試験 山本 和英、○水野 恒史、田中琢也、高橋弘充、深沢泰司(広島大)、田島宏康、釜江 常好(スタンフォード線形加速器センター)、金井義和、有元誠、植野優、片岡淳、河合誠之(東工大)、郡司修一(山形大)、斎藤芳隆、高橋忠幸 (ISAS/JAXA)、Mozsi Kiss、Cecilila M. Bettolo、Mark Pearce (Royal Insritute of Technology)、他PoGOLiteチーム Abstract: 硬X線で偏光観測を行うことは、シンクロトロン放射やコンプトン散乱、サイクロトロン吸収が絡む天体において、磁場や降着円盤の構造を解明する全く新しいプローブとなる。我々は2009年の気球による偏光観測を目指し、天体硬X線偏光検出器PoGOLite(Polarized Gamma-ray Observer -Light version)の開発を進めている。PoGOLiteは、コンプトン散乱の異方性を利用し 25--100~keVの硬X線領域に感度を持つ偏光計である。井戸型フォスウィッチカウンターのデザインを採用し、波形弁別により効率よくバックグラウンド除去を行う。散乱体、吸収体を兼ねたユニットを217本並べることで、大面積と低バックグラウンド化を両立させ、 6時間のフライトで、かにパルサーからの10％の偏光を検出できる等、かつてない高い感度を誇る。 　　これまで我々は、各コンポーネント毎の詳細試験(山本ほか、2005年秋の年会)やシンクロトロンビーム試験(金井ほか、2006年春の年会)等を通して順調に開発を行ってきた。現在はセンサーの生産を始めており、またフライトをにらんで読み出し回路の開発やセンサーの試験を行っており、観測エネルギー下限(25~keV)の光電吸収体で主検出部とシールド部の信号の区別が可能であることを確認するとともに、波形弁別性能の温度特性を取得した。本ポスターでは、これまでのPoGOLiteの開発試験、特にフライトデザインの読み出し回路と、小型シンチレーターを用いた簡易フォスウィッチおよび実機とを組み合わせた波形弁別性能について紹介する。 PoGOLite Mission: Expected Performance/Science: Detector Concept Compton Polarimeter made of plastic scint. High modulation factor Optimized for Hard X-ray (25-100keV) Adopt phoswich detector design with narrow FOV Well proven through balloon missions/Suzaku HXD Very low background Read-out through low noise PMT assembly Sensitive down to 1-2 keV Compton events Low BG/High Sensitivity Pulsar Emission Mechanism Accretion Disk Geometry Expected source and BG spectra Polar cap Caustic Outer gap Dyks and Rudak, ApJ, 2003 Side BGO Scint. Shield (BG rejection.) 100 mCrab(incident) 100 mCrab (detected) (b) BG total (CXB/ atmospheric downward/upward) Internationall Collaboration Cyg X-1 hard state: Proof of Comptonization Disk orientation Slow Plastic Scint. Collimator (FOV:5 deg2) 20 100 keV Crab Pulsar: Can distinguish models Japanese Consortium： PMT、Beam test, DAQ, Performance modeling Stanford University: Detector array, DAQ, Gondola and attitude control system, Payload integration and testing Swedish Consortium: Side-anticoincidence Shield, Observation planning Ecolo Polytechnique: Scintillator and crystal reflective material Modulation Curve for 100 mCrab source, 6h obs. polar cap caustic/slot gap outer gap Fast Plastic Scint. (Pol. measurement) PMT assembly (low noise) Bottom BGO Signal/BG=~4 MF=22.8+-0.7 % (30s) 10% pol. assumed ( ~10s detection) Schedule BG 2003 2004 2005 2006 2007 2008 azimuthal angle(rad) azimuthal angle (rad) azimuthal angle(rad) Balloon Flight! Proposal to NASA Proton Beam Test (Osaka) Sensor Complete Lots of science by each 6 hr. flight Collaboration with Swift/GLAST Long duration flight between Sweden and Canada KEK Beam Test KEK Beam Test Flight Instrument Integration Spring8/Argonne Beam Test Gondola Ready Second Proposal to NASA 1st prototype (fast scinti. 7 units) 2nd prototype (fast/slow 19 units+anti) Flight Instrument Integration and Test Pulse Shape Discrimination (PSD): Past Development: Side BGO Scintillator preamp output sampled with 20MS/s Position dependence by 137Cs PDC (main detector) Waveform-based PSD Slow Scintillator tube BGO/Slow Position dependence by 90Sr We sample preamplifier signal with 20 MS/s and distinguish fast/slow/BGO signal by examining the rise time. This waveform-based PSD allows a flexible and powerful event selection. p2 peak @ 2 or 3 CLK p4 p3 SAS (side shield) Flight Instrument Integration and Test p1（bottom） fast plastic p5 peak @ 14 CLK P6(top) Slow scinti. 1 ms Uniform Light Yield Uniform Light Yield peak hold 20cm SAS DAQ Development Temperature Dependence of BG rejection BGO Pulse Shape Discrimination Am only ( 6kHz ) Am + BG ( 9kHz ) Am + BG ( 15kHz ) Am + BG ( 20kHz ) Slow/BGO scintillator branch Ratio of slope between a fast branch and a slow/BGO branch represents the BG rejection power. High BG rejection is expected in operation temperature (<0oC) BGO/Fast Fast scinti. Slow/Fast BGO scinti. fast scintillator branch BG rejection PMT Self PHA with baseline subtraction Stable up to 20kHz Test with Phoswich Detector Cell (PDC) Beam Test at Argonne/KEK (2003, 2004, 2005 and 2007) A prototype module of the Front-End electronics provided by Hawaii University (left). The module was tested with PDC unit using 241Am and room BG (right). Argonne beam test in 2003, Mizuno et al. 2004, NIMA Proof of the design concept G4 simulation development KEK beam tests Flight PMT (2004) Kataoka et al. 2005, SPIE PDC in central unit (2005) Kanai et al. 2007 7 PDC units (2007) analysis in progress Modulation Curve for 73 keV beam MC prediction Data room BG (BG rejection power evaluation) 241Am run (light yield evaluation) 14 clock 14 clock beam direction rotated Azimuthal angle Summary : 3 clock delay subtracted peak 3 clock delay subtracted peak sliced and normalized Clear separation of fast branch and slow/BGO branch down to 15 keV (photo-absorption site). Coincidence with photo-absorption site will improve the BG rejection in Compton site (low energy). 55-60 keV / 35-40 keV / 25-30 keV 15-20 keV / 10-15 keV / 5-10 keV 0-5 keV 59.5 keV @ ~200ch Polarization measurement in Hard X-ray Unambiguous discrimination of emission mechanisms of accretion-powered pulsar, black-hole binaries and jet in m-QSOs/AGNs. PoGOLite Mission First balloon flight in year 2009 to observe Crab and/or Cyg X-1. Unprecedented high sensitivity in 20-100 keV Extensive Hardware/software development Waveform-based Pulse Shape Discrimination Flexible and powerful BG rejection Temperature dependence of light-yield and BG rejection power calibrated Clear separation of fast signals and slow/BGO signals. blowed light yield Fast: ~0.5 p.e. / keV BGO: ~0.25 p.e. /keV Slow:~1/2-2/3 of that of BGO single photo-electron @~13ch 59.5 keV @ ~410ch