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

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

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

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

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

Polarimeter Type Scattering Type is better in the sensitivity for hard X-ray non-imaging polatimetry. Scattering Type is better in the sensitivity for hard X-ray non-imaging polatimetry. ScatteringPhoto-electron-track Anistropy 1-sin 2  cos 2  sin 2  cos 2  Photon: travel straight Electron: scattered M >0.9 is possible, 0.5 is easy was obtained M   0.6 is max, is easyMax - E>5keV+ Imaging capability Pacciani et al SPIE M: Modulation contrast … modulation observed against 100% polarized beam  : Efficiency … the ratio of number of photons employed in the polarimetry to that incident to the polarimeter. M η 1/2 Minimum Detectable Polarization

Polarimetry using scattering target : employed in beam polarization calibration Ｅ KEK-PF 10keV beam by Hayashida et al. Spring8 20keV beam by Tokanai et al.

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

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

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

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

Experiment on the ground H8500 (52 x 52 x 28 mm 3) is very compact. The uniformity of anodes is fairly good.

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

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

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

Low energy extension Li target Ti filter Single Hit (Li) Events 5-20keV

Summary Scattering type is better for hard X-ray non- imaging polarimeter Scattering type is better for hard X-ray non- imaging polarimeter To optimize M,h,f, we propose to use segmented/active scatter as a target. To optimize M,h,f, we propose to use segmented/active scatter as a target. Ground experiments / balloon experiments are in progress. 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. 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) 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. Next step: Name the project.