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X-ray Polarimetry with gas proportional counters through rise-time

X-ray Polarimetry with gas proportional counters through rise-time. K. Hayashida, T. Horikawa, Y. Nakashima, H. Tsunemi (Osaka University, Japan). Bragg Crystal Reflection OSO8,ArielV satellites (1970’s) Compton Scattering Planned for Spectrum X-Gamma mission (1990’s)

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X-ray Polarimetry with gas proportional counters through rise-time

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  1. X-ray Polarimetry with gas proportional counters through rise-time K. Hayashida, T. Horikawa, Y. Nakashima, H. Tsunemi (Osaka University, Japan)

  2. Bragg Crystal Reflection OSO8,ArielV satellites (1970’s) Compton Scattering Planned for Spectrum X-Gamma mission (1990’s) Tracking Photo-electron Emission Direction X-ray CCD (Tsunemi et al., 1992) Micro electrodes Gas Chamber (Costa et al., 2001; Tanimori et al., 1999; Sakurai et al., 1996) X-ray Polarimeters in Astronomy Observations have been stagnant since 1970’s for more than 20 years.

  3. Anode Anode X-rayPhoton Anode Electron Cloud Rise Time = Long Rise Time = Short Rise Time Polarimeterusing Gas Proportional Counter • Proposed by Riegler et al., Sanford et al., in 1970. • We re-examined the method. (Hayashida et al., 1999, NIMA, 421,p.241) Working principle

  4. Ex=10-40keV (Pbeam~0.8; measured) Xe proportional counter Xe:736mmHg + CO2:25mmHg Multi cell type; 5cm depth, 5cmx30cm for each cell Anode 50mm Be; HV=1950V Experiment at Synchrotron Facility (1992-1993) Irradiate position =1.2cm from anode (Hayashida et al., 1999, NIMA, 421,p.241)

  5. Sampling the output pulse from CSPA with Digitized Oscilloscope. RT and PH are determined from the waveform data transferred to the computer Rise Time Measurement

  6. Results (Ex=34keV) RT vs Q RT distribution (Hayashida et al., 1999, NIMA, 421,p.241)

  7. Note: Xe-K edge =34.6keV Events were selected using PH. X-ray Energy dependence (Hayashida et al., 1999, NIMA, 421,p.241)

  8. Modulation Factor M Figure of merit for polarimter, larger the better. M (Hayashida et al., 1999, NIMA, 421,p.241)

  9. Thin Sn filter was placed at the beam exit, which produced Sn Ka,Kb fluorescent X-rays in addition to polarized 36 keV X-rays. Extra Experiment for Verification (Hayashida et al., 1999, NIMA, 421,p.241)

  10. Polarized X-ray Beam Line at Osaka Monochromatic beam with linear polarization degree of 40-50% is obtained. (Koike et al., 2000, SPIE4012, p.414) Measurement Chamber Double Crystal Spectrometer X-ray Generator

  11. 0.270 0.265 0.260 0.255 0.250 0.245 Experiment at Osaka Beam Line (2001-2002) angle E X-ray • Gas PCs • Ar gas flow type PC • Wire 50mm • Quenching gas (CH4) of various contents were examined. • Xe gas shield type PC (the same one used in Synchrotron Facility) • Data taking system was upgraded. 90,270 0,180 X-ray

  12. Gas Content Xe96.7%+CO23.3% Ar 90% +CH410% Ar99.3%+CH40.7% However, Results are … • Contents of Quenching Gas is very sensitive to RT. • Ar 99.3% +CH4 0.7% provided M of 0.05-0.1. Small! • More seriously, the same Xe counter used in 1992-1993 yielded M of less than 0.05. CONTRADICTION! Incident position 12mm from anode for Xe PC 10mm from anode for Ar PC

  13. EGS4 (Electron Gamma Shower Simulator ver4) + KEK low energy extensions Energy deposit and path of photoelectrons are simulated. Large effect of multiple scattering is observed. 1mm 10mm Preliminary Simulation using EGS4 Ar-Gas P=1atm Ex=20keV Ar-Gas P=1atm Ex=50keV

  14. M expected from EGS4 Simulation *) If multiple scattering does not exist, M would be 0.78. Dispersion of the distance to anode (s ) cm M Size s (cm) M • Small energy dependence • M=0.03-0.06 for Ar, <0.03 for Xe • NOTE: gas processes (diffusion, avalanche etc) is notconsidered.

  15. Strong dependence of X-ray incident position on RT was observed. Misalignment of rotation axis could have made an artifact modulation. But, the modulation should have 1 peak / 360deg, not like observed 2 peaks / 360deg. Sn-filter result was not explained with the misalignment, either. Solution of the Contradiction ? Anode Experiment at Synchrotron Facility is planed in this Autumn. 12mm

  16. Merit of PC polarimeter Large effective area is easily realized without mirrors. Suitable for balloon experiment. Pmin % (99% confidence) Feasibility Study PC polarimeter T=100ks Crab Nebula P=19% @2.6keV,5.2keV

  17. Summary • Gas proportional counter polarimeter with rise time measurement is introduced. • Previous experiment at Synchrotron facility provided M of 0.1-0.3 with Xe PC, while recent experiment (Xe PC, Ar PC) provides much smaller M. • Preliminary simulation also suggests M <0.1. • No firm solution has not yet been obtained for the contradiction. Sorry for inconclusive, confusing results.

  18. Merit of PC polarimter Large effective area is easily realized without mirrors. Suitable for balloon experiment Feasibility Study PC polarimter Pmin % (99% confidence) T=100ks

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