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

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

Rise Time Polarimeter using Gas Proportional Counter Proposed by Riegler et al., Sanford et al., in Proposed by Riegler et al., Sanford et al., in We re-examined the method. (Hayashida et al., 1999, NIMA, 421,p.241) We re-examined the method. (Hayashida et al., 1999, NIMA, 421,p.241) Anode Electro n Cloud Rise Time = Short Rise Time = Long Anode X-ray Photon Working principle

Experiment at Synchrotron Facility ( ) Ex=10-40keV (P beam ~0.8; measured) Ex=10-40keV (P beam ~0.8; measured) Xe proportional counter Xe proportional counter Xe:736mmHg + CO 2 :25mmHg Xe:736mmHg + CO 2 :25mmHg Multi cell type; 5cm depth, 5cmx30cm for each cell Multi cell type; 5cm depth, 5cmx30cm for each cell Anode 50  m Be; HV=1950V Anode 50  m Be; HV=1950V Irradiate position =1.2cm from anode (Hayashida et al., 1999, NIMA, 421,p.241)

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

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

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

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

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

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

Experiment at Osaka Beam Line ( ) Gas PCs Gas PCs Ar gas flow type PC Ar gas flow type PC Wire 50  m Wire 50  m Quenching gas (CH4) of various contents were examined. Quenching gas (CH4) of various contents were examined. Xe gas shield type PC (the same one used in Synchrotron Facility) Xe gas shield type PC (the same one used in Synchrotron Facility) Data taking system was upgraded. Data taking system was upgraded. X-ray E 90,270 0,180 angle

However, Results are … Gas Content Xe96.7%+CO 2 3.3% Ar 90% +CH 4 10% Ar99.3%+CH 4 0.7% Contents of Quenching Gas is very sensitive to RT. Contents of Quenching Gas is very sensitive to RT. Ar 99.3% +CH 4 0.7% provided M of Small! Ar 99.3% +CH 4 0.7% provided M of Small! More seriously, the same Xe counter used in yielded M of less than CONTRADICTION! More seriously, the same Xe counter used in yielded M of less than CONTRADICTION! Incident position 12mm from anode for Xe PC 10mm from anode for Ar PC

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

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

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

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

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

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