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GRI: the Gamma-Ray Imager Mission

GRI: the Gamma-Ray Imager Mission. Jürgen KNÖDLSEDER (CESR), on behalf of the GRI consortium. From INTEGRAL to GRI. INTEGRAL … reveals a large variety of gamma-ray source classes we want to zoom in to identify the sources and to study their emission mechanisms

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GRI: the Gamma-Ray Imager Mission

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  1. GRI: the Gamma-Ray Imager Mission Jürgen KNÖDLSEDER (CESR), on behalf of the GRI consortium

  2. From INTEGRAL to GRI INTEGRAL … reveals a large variety of gamma-ray source classeswe want to zoom in to identify the sources and to study their emission mechanisms discovers surprisingly hard emission from AXPs/SGRswe want to understand the nature of this emission uncovers absorbed AGN we want to determine their high-energy spectra to measure their contribution to the cosmic diffuse background unveils a challenging positron annihilation sky map we want to identify its origin and measure e+ annihilation in individual sources provides a unique view on nucleosynthesis (26Al, 60Fe, 44Ti) we want to understand the nature of supernovae explosions and their nucleosynthesis The time is ripe for … a focused, high-sensitivity gamma-ray mission

  3. GRI science Science question: How do thermonuclear supernova (Type Ia) explosions work? • Method: • Observe gamma-ray line lightcurve in a sizeable sample of Type Ia supernovae • Measure line profiles and line ratios in nearby Type Ia supernovae • Example: SN 1998bu 847keV line • CGRO upper limits  no discrimination between models • GRI sensitivity would easily allow to determine the valid explosion model Georgii et al. (2002) • Expected results: • Identify the primary thermonuclear supernova explosion mechanism • Determine the source of the intrinsic variety of SN Ia (sub-/super-luminous) • Calibrate the Type Ia supernovae standard candle

  4. GRI science Science question: How do galactic compact objects accelerate matter? • Method: • Measure the shape/amplitude of the high-energy emission tail as function of state • Search for 511 keV annihilation features • QPOs @ high-energy Morgan et al. (1997) Goldwurm et al. (1992) Grove et al. (1998) • Expected results: • Physical nature of hard component - relation to relativistic jets • Conditions for 511 keV line: sudden ejection events? • Fundamental GR frequencies: black-hole spin and jet ejection

  5. GRI science Science question: What is the nature of the soft gamma-ray emission of pulsars? • Method: • Measure spectra and pulse morphology changes (normal pulsars, AXPs, SGRs) • Measure the high-energy tails and cut-offs (AXPs, SGRs) • Example: AXP 1E 1841-045 • INTEGRAL detects hard tails in several AXPs and SGRs • COMPTEL upper limits suggest spectral break < 700 keV • GRI will measure the AXPs and SGRs high-energy spectra precisely (slope, cut-off energy) Kuiper et al. (2006) • Expected results: • Establish the gamma-ray production site and emission mechanism in pulsars • Identify the nature of hard tails in AXPs and SGRs

  6. GRI science Science question: What is the nature of the AGN soft gamma-ray emission? • Method: • Measure the AGN high-energy spectra and their variety in a sizeable sample • Determine the AGN cut-off energy (as function of AGN type) Risaliti (2002) Weidenspointner (1998) ? • Expected results: • AGN spectral cut-off energy and variety • AGN contribution to cosmic gamma-ray background radiation • Origin of the high-energy emission (disk or jet)

  7. GRI science Science question: What is the source of galactic positrons? • Method: • Search for 511 keV annihilation features in potential candidate sources • Image the central bulge region Novae, SN Ia GRB/Hypernovae XRB µQSO Knödlseder et al. (2005) • Expected results: • Identification of primary galactic positron source • Determine positron escape fractions and yields • Positron source distribution in the central bulge

  8. GRI science Science question: How do massive stars explode? • Method: • Measure gamma-ray line intensities and profiles in core-collapse supernovae • Measure line and continuum emission in galactic supernova remnants • Search for gamma-ray line emission from massive star associations SN 1987A no mixing mixing Leising & Share (1990) Diehl & Timmes (1998) • Expected results: • Information about dynamics, mixing and symmetry during core collapse • Nucleosynthetic stellar yield calibrations • Core-collapse SN contribution to galactic positron budget

  9. GRI science Science question: How do Solar flares accelerate particles to very high energies? • Method: • Spectro-imaging of the prompt g-ray emission from flaring active regions • Measure the development of the radioactive patch after the flares Tatischeff et al. (2006) Hurford et al. (2005) • Expected results: • Determine the composition and energy spectrum of the accelerated particles • Identify the acceleration mechanism • Observe the mixing processes in the Solar convection zone

  10. GRI science Gamma-Ray Polarization - the ultimate dimension: Probing the nature of high energy emission The combined measurement of polarization angle and degree of linear polarization provides vital information about the emission mechanisms • Pulsars & Supernova Remnants: • understand the relation between gamma-ray and multi-l emissions • discriminate between pulsars models (polar gap vs. outer cap)~40% polarization has been measured by INTEGRAL from the Crab pulsar • Soft Gamma-Ray Repeaters and AXP: • probe magnetic photon splitting~25% polarization expected • Compact objects: • probe the geometry of the accretion disk~30-60% polarization possible for optiocally thin disk (~10% for thick disks)

  11. GRI science requirements Requirements for a future gamma-ray mission: Access to non-thermal Universe and gamma-ray lines cover soft gamma-ray energy range (~150 keV - 1 MeV) Sensitivity leap in soft gamma-raysreach 50 µCrab Contemporaneous observation down to hard X-raysmonitoring capability in the 20 - 200 keV band Angular resolution for counterpart identification arcmin Polarimetry for identification of emission processes

  12. Taking the sensitivity leap Courtesy: Peter von Ballmoos

  13. GRI sketch detector spacecraft optics spacecraft face-on edge-on structure / spacecraft detector 3.8 m DSC crystal lens mask 60 - 80 m sketch not to scale

  14. Lens perfomances 60" 30" • Lens summary (optimisation studies still ongoing): • 13772 Ge crystals, 20697 Cu crystals • Lens effective area: 500 - 900 cm2 @ 160 - 520 keV & 700 cm2 @ 800 - 900 keV • Mosaicity (= angular resolution): 30” (high-energy) - 60” (low-energy)

  15. Formation requirements • Formation Flight: • R/F metrology for coarse formation control • Optical metrology for fine formation control

  16. Lens crystals SiGe crystal boule (courtesy: IKZ) Cu crystal with mosaicities of30 - 60 arcsec are available (courtesy: ILL) • Lens crystals: • Ge crystals have already been used for CLAIRE balloon project • Cu crystals with the required properties are available • Massive (several 10 000) crystal cutting / characterisation needs to be developed

  17. Crystal developments Goal: Improve the efficiency of crystals Silver and gold crystals Better diffraction efficiency for the same mass Gradient crystals Reduce the backreflection Efficiency gain of factor ~2 measured(courtesy: B. Smither) Composite crystals Build a “gradient” crystals from individual crystal wafers (e.g. Si)(courtesy: N. Barrière)

  18. Lens requirements Cu crystal monochromator (courtesy: ILL) CLAIRE Ge crystal lens (integration) (courtesy: P. von Ballmoos) • Lens requirements: • Mounting and control of several 10 000 crystal is a technological challenge • R&D work underway

  19. Lens angular response 3 point source lens response (event density on detector plane)on axis, 2’ off axis, 4’ off axis GRI imaging of 4 point sources model reconstruction • GRI imaging: • FOV defined by detector area (20 x 20 cm  10 arcmin diameter) • Dithering allows imaging with ~ arcmin resolution (precision set by mosaicity)

  20. Lens detector Lens detector basic elements Detector stack High QE requires detector thickness of several cm (feasible with stack) Stack can be used as Compton camera for background reduction Compton camera measures gamma-ray polarization Design considerationsstack built of CZT (modest energy resolution) or Ge (cooling, annealing) additional Si layers on top of stack may improve Compton camera? BGO shield as collimator and active background reduction? LaBr3 scintillator on bottom may improve QE at high energies? • Detector design under study Si tracker (optional) BGO shield (optional) CZT or Ge stack LaBr3 absorber (optional) sketch not to scale

  21. Hard X-ray monitor Use coded mask for low-energy (20-200 keV) coverage Collimation considerably reduces extragalactic background (< 100 keV) Double CZT layertop layer used for photoelectric absorption bottom layer used as shield (low E) and as Compton absorber (high E) collimator sketch not to scale passive shield CZT layer(s) lens detector

  22. Detector technology Current developments Low-noise GeD pre-amps 1.6 keV FWHM(courtesy: S. Boggs) Cross-strip GeDs Vol: 81 cm3, Res: 1.6 mm3 (courtesy: S. Boggs) Development model for large area hybridised CZT detectors(courtesy: B. Swinyard) 256 pixel CZT detector Thickness 5 mm (courtesy: E. Caroli) Wide-band ASIC (20 - 2000 keV) 2x8 channels; < 1 mW/channel (courtesy: E. Caroli)

  23. Hard X-ray monitor Use single reflection multilayer mirror instead of a coded mask Advantages w/r mask better hard X-ray sensitivity small/light detector Disadvantages w/r maskno imaging (small or no FOV) technical feasibility needs still to be demonstrated Example: HEFT mirror Material combination: W/Si Substrate thickness: 0.2 mm Substrate: Si Mirror length: 60 cm Mirror radii: 9 - 44 cm Estimated effective area

  24. Allsky monitor The use of a Compton stack as lens detector offers an interesting possibility Use the lens detector as allsky monitor GRI can find its own ToO Additional survey science (monitoring of source variability , diffuse emission) Use of Compton kinematics for allsky monitoring (courtesy: A. Zoglauer)

  25. GRI performance summary Requirements: baseline to fulfill GRI science objectives Goals: possible evolutions (to be studied)

  26. GRI summary GRI adresses: The physics of supernova explosionsParticle acceleration in compacts objects and SNRs The nature of pulsar high-energy emission The high-energy emission of AGN GRI offers: An unprecedented sensitivity leap in soft gamma-rays (observation of hundreds of XRB and AGN in gamma-rays) Simultaneous soft gamma-ray and hard X-ray coverage Arcmin angular resolution Polarimetry GRI implies: A new technology to observe the gamma-ray sky Formation flying A moderate launch mass (~ 2 tonnes total in L2)

  27. The GRI consortium DNSC (Copenhagen) University of Coïmbra APC (Paris) CESR (Toulouse) CSNSM (Orsay) IAP (Paris) ILL (Grenoble) LAM (Marseille) IOFFE (St. Petersburg) SINP, MSU (Moskow) CNM (Barcelona) IEEC/CSIC (Barcelona) IFAE (Barcelona) MPE (Garching) Mullard Space Science Laboratory (London) Rutherford Appleton Laboratory University of Southampton INAF Brera INAF-IASF Bologna INAF-IASF Milano INAF-IASF Palermo INAF-IASF Roma Observatory of Roma University of Ferrara Argonne National Laboratory (Chicago) Space Science Laboratory (Berkeley) SRON (Utrecht) University of Utrecht

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