Polarimeter for Small Satellite Design, Feasibility Study, and Ground Experiments + Balloon Experiment

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1 Hard X-ray X Polarimeter for Small Satellite Design, Feasibility Study, and Ground Experiments + Balloon Experiment K. Hayashida (Osaka University), T. Mihara (RIKEN), S. Gunji,, F. Tokanai(Yamagata University) SPIE@Glasgow 2004/6/22

2 X-ray Polarimetry It is still an unexploited field. conf.slac.stanford.edu/xray_polar/ We are going to make a plan yet has no name Energy range=hard X-ray X (20-80keV) Main Targets=Bright compact sources Optics=Not to use Polarimeter type = Scattering

3 Targets of X-ray X Polarimetry Synchrotron Radiation SNR Pulsar Nebulae, Shell Type Clusters of galaxies Blazars Quasars Scattered Radiation Accretion disk around black hole Accretion Torus Seyfert galaxies Magnetic field and scattering Pulsars Reflection by Accretion Disk Polarization Degree CXC/NASA X-ray Energy (kev)

4 We aim primarily hard X-rays X (20-80keV) Non thermal component is prominent in the hard X-ray band. Energy dependence of polarization is important. Polarization below 10keV was detected in 1970 but has not yet been the hard X-ray X band. Various projects for soft X-ray X (AXP, PLEXAS,SXP) polarimetry and gamma-ray polarimetry (POGO,..) are proposed, though XPE and POGO cover some part of hard X-rays. X Balloon experiments prior to a satellite are effective for hard X-ray X band. (We began this study for the NeXT satellite in which hard X-ray X super mirrors will be employed.)

5 Is imaging capability essential for hard X-ray X polarimetry? Polarization map would be amazing, but diffuse (>arcmin arcmin) ) sources are estimated to be dim in 20-80keV. Crab is exceptional. The 2 nd brightest Crab like= Kes75 3mCrab Tycho,, SN1006 1mCrab-2mCrab Coma cluster 2mCrab We should focus on bright point-like sources first. Collection power of super mirror is very attractive, but might be too expensive for a small satellite. for 1HXT NeXT HXT AE ( ) ~ 400( Ex/ 20 kev) cm 1 2

6 M: Modulation contrast modulation observed against 100% polarized beam η: Efficiency the ratio of number of photons employed in the polarimetry to that incident to the polarimeter. Pacciani et al SPIE Polarimeter Type Scattering Photo-electron electron-tracktrack Anistropy 1-sin 2 θcos 2 φ sin 2 θcos 2 φ Photon: travel straight Electron: scattered M >0.9 is possible, 0.5 is easy was obtained Mη 1/2 0.6 is max, is easy Max ~0.07@20keV - E>5keV + Imaging capability Minimum Detectable Polarization Scattering Type is better in the sensitivity for hard X-ray X non-imaging polatimetry. M 1/2

7 Polarimetry using scattering target : employed in beam polarization calibration 600 counts rotation angle KEK-PF 10keV beam by Hayashida et al. Spring8 20keV beam by Tokanai et al.

8 Top view Side view Scattering target Detector Mη 1/2 1/2 x f 1/2 M~1 η<<1 M~0.5 η~0.6 f: effective area of scatter /total area f<<1 f~1/4 GAPOM Mihara et al. M should be higher to reduce systematics M~0.25 η~0.6 f~1

9 Segmented/Active Scatter Polarimeter Scatter=Plastic Scintillator (e.g. 2mmx2mmx40mm x 54) Whole detector is actrively Shielded by BGO or CsI X-ray 18mm Multi-Anode Position sensitive PMT Absrber=CdTe (e.g.2mmx0.5mmx40mmx32)(or CSI)

10 Efficiency for for three kinds of events Photo Absorption Compton recoil not detected Compton recoil detected Plastic CdTe or CSI Absorped event Single event Double event

11 Efficiency η and Modulation Contrast X-rays are irradiated uniformly on the plastic scintillator Single hit events Double hit events Double hit events M~0.55 Single hit events M~0.28

12 Top View Experiment on the ground plastic scintillator 6 mm CsI(Tl) 52 mm H8500 (52 x 52 x 28 mm 3) is very compact. The uniformity of anodes is fairly good.

13 Balloon Experiment by Yamagata Group (Gunji( et al.) Collimator Scinti

14 Balloon Flight on 2004June3rd from Sanriku-Balloon Center Raw Counting Rate not filtered with ANTI Altitude (km) Detectors functioned properly. Did it detect Crab? How about its polarization degree?

15 25 units of Balloon experiments ->Satellite Polarization Sensitivity Double Hit Events 40-80keV Single Hit Events 20-40keV Considering BGD 10 Without BGD 100ks ks 1 1Ms 1 1Ms Flux (mcrab) Flux (mcrab)

16 Low energy extension Top View Single Hit (Li) Events 5-20keV Li target 52 mm plastic scintillator 6 mm CsI(Tl) Ti filter Flux (mcrab)

17 Summary Scattering type is better for hard X-ray X non- imaging polarimeter To optimize M,h,f,, we propose to use segmented/active scatter as a target. Ground experiments / balloon experiments are in progress. Low energy extension is possible by inserting Li target at the center. Increase the PMT sensitivity will also lower the energy threshold. Electric power and circuits is the issue we have to consider. (Heritage of Astro-E2 HXD, NeXT SGD may be useful) Next step: Name the project.