Soft Gamma-ray Detector (SGD) for the NeXT mission and beyond Astro-E2 Tadayuki Takahashi

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1 T.Takahashi, Astronomy with Radioactivies IV,2003 Soft Gamma-ray Detector (SGD) for the NeXT mission and beyond Astro-E2 Tadayuki Takahashi Institute of Space and Astronautical Science (ISAS, Japan) ? ISAS/U-Tokyo/SLAC/Hiroshima U./Osaka U./Saitama U./ Riken/Kanazawa U. (the SGD collaboration) g-ray Detector

2 Introduction - filling the sensitivity gap - Gap-1 Gap-2 The NeXT (New X-ray Telescope) mission Next generation Multi-band mission to study the non-thermal universe (6th X-ray satellite in Japan, hope to be launched in 2010) Development of highly-sensitive detector in Soft Gamma-ray energy bands (sub-mev & MeV) is crucial issue. Our Approach Extend the energy coverage from X-ray to higher energy (from Gap-1 to Gap-2) Multi-band observation (from X-rays) is important (and productive), to study the NON-THERMAL universe. Apply the developedtechnology to higher energy band for the Gap-2

3 What s next in the NeXT mission Super Mirror + Hard X-ray Imager High resolution X-ray detector (FWHM = 3 ev at 6 kev) Soft Gamma-ray Detector (30 kev kev) (+polarization) Super Mirror ( kev ) 30 HPD g-ray Detector focal length 8-12 m Spectrometer Hard X-ray Imager ISAS Hard X-ray Imager SGD

4 High Resolution CdTe detector - New Detector Material for the future mission - High Z semiconductor (ZCd = 48, ZTe = 52) -> Significant Progress in 1990 s (Takahashi et al. IEEE NS49, 3,2002, review by Takahashi & Watanabe, IEEE NS48, 4, 950, 2001) ISAS project High Energy Resolution see posters by Tanaka et al. and by Mitani et al. 137 Cs 12.8mm Fine Position Resolution CdTe Gamma-ray Imager (pixel size 200 µm) ISAS & Bonn U. 662keV FWHM 2.1 kev

5 T.Takahashi, Astronomy with Radioactivies IV,2003 To improve the sensitivity in the sub-mev region Key issues: Cosmic X-ray Background (CXB) from the FOV Non X-ray Background (Internal Background) Confusion Limit in the FOV/Error circle kev HXD for Astro E-2 Si GSO BGO HXD Concept (High Signal to Background ratio) tight active shields (Well-type shield) the collimated narrow field of view (0.5 degree at 100 kev, 4 degree at 500keV by a fine collimator and BGO) Compton suppression for high energy gamma-ray the compound-eye configuration. Internal Background limits the sensitivity. How can we improve this for the NeXT?

6 Semiconductor Compton Telescope for the pointing observation If we replace GSO+Si PIN diode used in the HXD by. Stack of Si strips High Resolution CdTe pixels Well-type Active shield CG by Yuriko S and put them into the well

7 New Concept: Narrow FOV Compton Camera Gamma-rays from the source come from the narrow FOV (0.5-3 deg FWHM) (Direction is Given!) Select two hits events and accept only if (E1+ E2) E2 = (E1+ E2)(1- cosq) 1+ m e c 2 This condition is expected to get rid of most of internal background. No need to worry about the sequence if scattering angle is below (Adoption of Fine Coll. is still an option) (Takahashi et al. 2003, SPIE, vol. 4851) First scattering (E1) has lower energy

8 Narrow FOV Compton Camera T.Takahashi, Astronomy with Radioactivies IV,2003 Lower accidental coincidences Imaging capability with an angular resolution of ~degree, Important for modeling the background spectrum for the Non-Compton mode

9 Narrow FOV Compton Camera T.Takahashi, Astronomy with Radioactivies IV, layers of 0.5 mm-thick Strip Strip detectors 6 mm-thick CdTe Pixel (res. 1mm) total Effective Area one Compton + Abs. Polarization (200 kev) (Scattered at Si and absorped in CdTe) Lower accidental coincidences Imaging capability with an angular resolution of ~degree, Important for modeling the background spectrum for the Non-Compton mode

10 T.Takahashi, Astronomy with Radioactivies IV,2003 Key technologies under development 25mm/400micron pitch 1. High resolution Silicon Strip detector 2. High resolution CdTe pixels/strips (see posters by Mitani and Tanaka) 3. Low Noise ASIC 4. Signal extraction (bump bonding) Uno etal., 2003 Si strip with a new ASIC 1200 x10 2 ΔE =1.5keV(FWHM) 241 Am 13.9 kev kev Tajima et al. 2003, SPIE, kev kev kev 200 Takahashi etal., IEEE, NS. 48, 3, Energy [kev]

11 Compton Reconstruction

12 Sensitivity of the NeXT mission kev High Sensitivity for both Line and Continuum Polarization measurement 100 ks Line Cont. CasA 68keV This is not the end of the story

13 Semiconductor Multi Compton Telescope (SMCT) For the future MeV Gamma-ray Astronomy Maybe by a big mission Or by a small satellite Or by a balloon Or by a formation flight

14 CdTe telescope Eff. of MultiCompton CdTe has a high Compton Efficiency for the energy above 300 kev ( Eff. = 40% at 1MeV for 80 layers, 250 cm 2 ) Compact Compton Telescope for micro/small satellite (important to increase chances of the mission) Conceptual design of CdTe SMCT 25cm Si Si CdTe 80 layers Si CdTe Note: Angular resolution CdTe 80 layers of 0.5 mm thick CdTe (and/or Si) Large FOV Polarization

15 Active Pair Telescope (APT) Above 10 MeV, Pair Production is the dominant process GLAST Gamma-ray below 100 MeV would be absorbed by conversion foil (loose efficiency) radiation length (r.l.)of CdTe :1.52cm 0.5 mm thick CdTe --> 0.03 r.l (same as the conversion foil used in GLAST) -> can be used as an active CONVERTER as well as a calorimeter (total r.l. -> 2.6 r.l. for 80 layers ) Fully active pair production telescope CdTe APT (Takahashi et al. 2003, SPIE, vol. 4851) Highly Sensitive detector below 100 MeV

16 Summary Development of High Resolution CdTe and Si strips/pixels are in progress. Pixels, Strips and related technology for CdTe/CZT/Si are now well in our hands. ex. Focal plane detector for the super mirror New detector concepts Narrow FOV Compton telescope (SGD) for the NeXT mission (upto several hundred kev, polarization) Semiconductor Multi Compton Telescope (SMCT) for MeV gamma-rays Active Pair-production Telescope (APT) For the demonstration, we will have balloon missions in