1. Hiroyasu Tajima Stanford Linear Accelerator Center Nov 3–8, 2002 VERTEX2002, Kailua-Kona, Hawaii Gamma-ray Polarimetry ~ Astrophysics Application ~

2. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Outline Introduction. Concepts. Key features (requirements.) Instrument description.  Silicon Strip Detector System. Double-sided SSD. Low noise front-end VLSI. Results.  Noise performance.  Energy resolution. Conclusions and future prospects.

3. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Polarization in Astrophysics Gamma-ray is excellent probe to study particle acceleration mechanism in BHs and pulsars. Polarization is important parameter to understand gamma-ray production mechanism.  Inverse Compton Scattering. Polarization depends on scattering angle. Geometrical information.  Synchrotron Radiation. Polarization is perpendicular to magnetic field direction.

4. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Soft Gamma-ray (X-ray) Imaging Coded mask Compton telescope X-ray mirror Well-type Phoswich

5. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Polarization Measurement Photoelectric absorption Compton Scattering  Polarization depends on scattering angle, photon energy. e EE EE E’  Polarization vector

6. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Polarimetry with Micro Pattern Gas Detectors R. Bellazzini, INFN Pisa

7. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Analyzing Power 5.9 keV unpolarized5.4 keV polarized Analyzing power = (C max  C max )/(C max  C max ) ~ 50% C max C min

8. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Multiple Compton Technique Proposed by T. Kamae et al. 1987  E1E1 E3E3 E2E2 11 22

9. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Key Features (Requirements) High energy resolution: ~ 1 keV (FWHM).  High angular resolution: ~ 1 o (FWHM).  High background rejection. Constraints from Compton kinematics Polarimetry. Large Field-of-View: > 2 sr. Wide energy band: 0.05–20 MeV. Low weight.  No heavy calorimeter. ~ 120 e – (RMS)

10. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Angular Resolution Doppler broadening will limit ultimate angular resolution.

11. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Source Localization

12. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 With 10X Better Resolution…

13. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Semiconductor Multiple-Compton Telescope photo- absorption Compton Scattering pair- creation Si Detector CdTe Detector Si CdTe Doppler broadening is much smaller in Si.

14. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Collaboration Hiroyasu Tajima, T. Kamae Stanford Linear Accelerator Center T. Takahashi, K. Nakazawa Institute of Space and Astronautical Science Y. Fukazawa Hiroshima University M. Nomachi Osaka University

15. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Performance Si is essential for wide energy band. 25cm 80 layers 80 layers of 0.5 mm thick Si and CdTe Takahashi (ISAS) Si CdTe

16. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Compton Kinematics Background suppression EGS4.4 MC

17. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Polarization Sensitivity EGS4.4 MC 100% polarized, 100 keV |cos  | < 0.6 Analyzing power ~ 75%

18. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Recent Development of CdTe Detector Tremendous amount of progress has been made.  Highly uniform, fully active sensors can be produced. 122 keV FWHM 1.35 keV 5 o C Bias 800V (16 kV/cm) 57 Co No Tail Takahashi et al. 1999 NIM A 436 (see e.g. Takahashi et al. IEEE 2002, June and review by Takahashi & Watanabe IEEE 2001,48,4) -25 ℃

19. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 CdTe Gamma-ray Imager 5cm Pixel 1.2x1.2mm 2 1024 pixels Pixel 0.2x0.2mm 2 1024 pixels CdTe Pixel 0.67x0.67mm 2 400 pixels 2dim ASIC (100pixel) 2mm bump bonding ISAS/MHI Patent Applying Takahashi (ISAS)

20. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Si Strip Detector System Why Double-sided Si Strip Detector?  No self-trigger for CCD.  Hybrid-pixel detector increases non-active material.  Monolithic-pixel detector cannot be produced in large volume. System configuration. V Double-sided Si Strip Detector Front-end VLSI VA32TA RC chip R

21. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Double-sided Si Strip Detector 2.56cm x 2.56 cm  ~1/2 length of full size sensor. 300 µm thick, 400 µm pitch, 100 µm gap. Strip capacitance: ~ 5.5 pF (measured.) Junction side Ohmic side

22. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 VA32TA: Low Noise Front-end VLSI Low noise  Front-end MOSFET geometry optimized for small capacitance load in 1.2 µm process. Internal DAC (4-bit trim DAC, bias). Fabricated in AMS 0.35 µm process  Radiation hard to 20 MRad. SEU (single event upset) tolerant. Ideas ASA

23. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Prototype System AC configuration DC configuration VA32TA Singled-sided SSD RC chip

24. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Noise Analysis Amplifier noise: capacitance load. Shot noise: leakage current. Thermal noise: detector bias resistance. 120 e – (RMS)

25. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Noise Performance Summary Config.Temp.  peak Noise (FWHM) MeasuredExpected AC 20 o C 2 µs1.7 keV1.6 keV 4 µs1.7 keV1.6 keV 0 o C 2 µs1.6 keV1.4 keV 4 µs1.4 keV1.1 keV DC0 o C 2 µs1.2 keV1.1 keV 4 µs1.0 keV0.9 keV

26. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 241 Am Spectrum DC configuration, 0 o C

27. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 241 Am Fit

28. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 57 Co Spectrum Compton edge DC configuration, 0 o C

29. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 57 Co Fit

30. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Energy Resolution Summary Config.Temp.  peak Resolution (FWHM) 60 keV122 keV AC 20 o C 2 µs1.9 keV2.1 keV 4 µs2.1 keV2.3 keV 0 o C 2 µs1.8 keV1.9 keV 4 µs1.7 keV1.8 keV DC0 o C 2 µs1.6 keV 4 µs1.3 keV

31. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Conclusions and Future Prospects Energy resolution measured using prototypes.  1.3 keV @0 o C for 60 and 122 keV X-rays.  Noise sources are well understood. Imaging test with stacked DSSD prototypes.  Polarization measurements. Further improvements are required for larger full- sized sensors.  Optimization of front-end MOSFET in 0.35 µm process.  Reduction of detector capacitance. Sensor thickness: 300 µm  400 µm.  Pitch adapter.

32. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Sensitivity Gap… Sensitivity (MeV/cm 2 /s) No approved mission to cover 0.1–20 MeV energy band.  Sensitivity is mostly limited by BG. COMPTEL EGRET Astro-E2 GLAST INTEGRAL EXIST OSSE Next generation Compton telescope

33. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Liquid Xenon TPC LXeGRIT collaboration

34. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002 Germanium Compton Telescope

35. Gamma-ray Polarimetry, H. Tajima, Vertex 2002, Kailua-Kona, Hawaii, Nov. 8, 2002