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SLAC - AIS, 2 Sept 2009
The next Frontier in Gamma-Ray Astronomy:
Development of Detectors for the MeV range ~0.1 – 100 MeV
Gottfried KanbachMax-Planck-Institut für extraterrestrische Physik, Garching, Germany
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The electromagnetic spectrum and the transparency of Earth’s atmosphere
Energy
Č
Satellite Telescopes
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Past: Compton Gamma-Ray Observatory (1991-2000)
OSSE
COMPTEL EGRET
BATSE
0.01 0.1 1 10 100 1000 10000 MeVBATSE,OSSE COMPTEL EGRET
CGRO
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COMPTEL, 1-30 MeV
EGRET, >100 MeV
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Galactic γ-ray line emission511 keVFWHM 2.95 keV
P. Jean et al.
R. Diehl et al.
26Al, 1809 keVFWHM 3.1 keV
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Present: Fermi Gamma-Ray Space Telescope (2008 - )
0.01 0.1 1 10 100 1000 10000 MeVFermi LAT
CGRO
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The‚MeV‘ gap !
Situation of multi-wavelength High-Energy Astronomy: Severe sensitivity deficit at MeV energies
FERMI-LAT
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COMPTEL, 1-30 MeV
Toscanelli's World Map, 1474
Fermi 3 mo. sky survey>100 MeV
also:Air Cerenkov Telescopes
HESS, Veritas, Magic
ROSAT PSPC0.1-2 keV
also: SWIFT, INTEGRAL
coming: NuStar, Astro-H
the gamma-raymainland:~50 Mev to ~TeV
the X-ray continent:~100 ev to ~100 keV
the MeV continent
Future ???
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Astrophysics in the ‚MeV‘ regionMeV300
100
30
10
3
1
0.3
0.1
nuclear binding energy~ 8 MeV
„the starting line of acceleration...“
electron restmass 0.511 MeV
Nuclear Processes cosmic accelerators
non-thermal continuum(Bremsstrahlung, synchro-cyclotron radiation,
inverse Compton,...)
nuclear γ-lines
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Astrophysics in the ‚MeV‘ regionMeV300
100
30
10
3
1
0.3
0.1
Nuclear processes& Nucleosynthesis
cosmic accelerators
511 keV: novae; solar flares;GC sources
galactic radioactivity 26Al; 60Fe, CRs & ISMSNeyoung SNRs 44Ti
stellar & solar nuclear reactionsSED maxima of manyFermi/COMPTEL Blazars
non-thermal spectrain black-hole binaries,micro-quasars
GRB: spectra & polarization
Fermi LAT sources: pulsars, unids,binaries, AGN, etc.
Galactic and extragalacticdiffuse background
nuclear resonance absorption
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• photon interaction cross-sections gothrough a minimum
• double Compton scattering efficiencies low• Compton event reconstruction incomplete
and limited by Doppler broadening• Pair events limited by nuclear recoil
• Instrumental background in space isstrong
Why is the sensitivity in theMeV region so low?
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Compton Scattering (0.2-10 MeV)Photon Crossection MinimumScattered photons with long rangeTelescope:Compton Camera Coincidence System
Pair Creation (> 10 MeV)Photons completelyconverted to e+e-
Telescope:Tracking chambersto visualize the pairs
CrossSection
Energy
Photoeffect(< 100 keV)
Photons effectivelyblocked and stopped
Telescopes:
CollimatorsCoded Mask Systems
Detection of Gamma Radiation
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COMPTEL, 1-30 MeV
COMPTEL
Trigger: t.o.f. delayed coincidence
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Schematics to illustrate COMPTEL instrumental background events
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Effective Area and Sensitivity
Source: Ns = A T ∫ Isrc(E) ε(E) dE
Background: Nb = A T ∫ Isky(E) ε(E) dE + Ninst
Significance: nσ = Ns / √ Nb
Detection threshold:
Fthresh =nσ √ Nb
A ε T ΔE
Instrumental Background:~ 100 keV bis ~ 10 MeV
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MeV Telescope RequirementsImprove:
sensitivity (reduce background), field of view, angular resolution Imaging
effective area (= count rates) Timing
energy resolution over large E rangeSpectroscopy
control detector systematics Polarimetry
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Imaging, Timing, Spectroscopy, Polarimetry
• Mapping the Sky:deep, continuous, survey from ~0.3-100 MeVDiffuse and localized sources
• Variabilityfast: GRBs, transients, SGRs, Novae
solar flares, pulsars (periodic)slow: AGN, SNe
• Broadband spectra:SED characteristic for particles, fields & geometry
• Narrowband spectra:Cosmic radioactivity with short and long half-livesNuclear resonance absorption
• Polarization: Pulsars, GRBs, AGN
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MeV Telescope Concepts
Classical Compton Event Circles
(no electron tracking)
Compton arcs for events with electron track or 3rd
interaction
Direct imaging of pair-creation events
Detectors using Compton Scattering and Pair CreationCOMPTEL, EGRET, LAT
Collimated Detectors: OSSE, RHESSI, ASTRO-H
Coded Mask Systems:INTEGRAL, SWIFT
Laue Lens Telescope:DUAL
20-50m
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MPE Developments 1996-2004:The Medium Energy Gamma-Ray Astronomy
Project MEGA
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Proof of principle:The MEGA Compton/Pair
telescope prototype
Tracker: double sided
Si strip detectors
Calorimeter: 2(3)D resolving
CsI/PIN diodevoxel array
Compton Scattering:
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Prototype and Full-size Instrument(GEANT models, status 2001)
30 layers of Si strip detectors36 x 36 cm2 , 0.5 mm thick
Full CsI Calorimeter
~10 layers of Si strip detectors20 calorimeter modules
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Prototype Tracker: 11 layers with 3x3 SSDs (ea. 6x6cm2, 470μm pitch)Total Si area ~ 4000 cm2, ΔEFWHM: > 15 keV @ 122 keV
Calorimeter: 20 modules of 120 CsI(Tl) bars each, 5x5x[20,40,80] mm3
PIN diode readout (Hamamatsu), ΔEFWHM : > 70 keV @ 662 keVΩ fill factor lower hemisphere ~ 40%
Aeff estimate :
Aeff = (1-e-μd ) Ageomη= 16 cm2 η
with η = 0.4 x 0.3Aeff ~ 2 cm2
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Tracker:11 layers, 8448 strips
Calorimeter:20 blocks, 2400 crystals
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Layout of the MEGA double sided Si strip detectors
Design: MPE HLL (Semiconductor Lab. of MPE, Garching)Fabrication: Eurisys, Strasbourg, FranceRef: Bloser et al., NIM, 512, 228 (2003)
• wafers: 6x6x0.5 cm3 ; 128x128 strips• n-side strips separated by p-spray implantation• AC coupling: Al strips on an insulating layer• Punch-through bias between strips and common bias ring• Multiple guard rings on p-side
p-sidelayout
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3x3 wafers mounted on grid structure (PEEK frame)
Shadow of 6mm Pb mask irradiated with 57Co
Resolution of tracker measured with muons: 290µm
ΔEFWHM: ~ 15 keV
18 cm
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Calorimeter Modules• 120 CsI crystal bars 0.5x 0.5x [2, 4 , 8] cm3 / module• Monolithic 10 x 12 PIN Diode Array with 5x5 mm2 pixels
(Hamamatsu)• R/O electronics integrated on the backside of the Hybrids.• Energy resolution @ 662 keV: ~ 10 % FWHM (3-D)• Spatial resolution: x-y: pixel size; z:~1.5 cm
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Calibration of MEGA: Free Electron Laser, Inverse Compton Beam
(HIγS FELL, Duke U., NC) 2003
injection from Linac@ 270 MeV
;4)(1
4;
2;
)2/1(2;
22
2
2
2
2
cmE
EE
cmeBK
KhcE
cmE
e
ph
ph
e
www
wwph
e
e
γγθ
γπλ
λγγ γ
++≅=
+==
electron laser photon energy IC gamma-rayenergy (UV-IR) energy
RF cavity
wiggler mirror
e--bunch 1
e--bunch 2 laser pulse 1
γ-ray beamE-vector horizontal
0.7–50 MeV
mirror
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Angular resolution in the Compton range
0.05.0
10.015.020.0
100 1000 10000
Energy [keV]
Angu
lar r
esol
utio
n as
FW
HM
of A
RM
[deg
]
Tracked Not tracked
2 MeV 5 MeV 8 MeV
Increase due to incomplete absorption (electron escapes, secondary photon leaks)
20°
Width of angular resolutiondominated by energy resolution in calorimeters (e.g. 8 cm calorimeters: 15% - 22%) and notby physical limits!
Doppler-broadening: ~0.23° at 2 MeV in Silicon
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Angular resolution in the Pair creation range12 MeV 25 MeV 49 MeV
Increased influence of Molière-scattering and of unknown recoil of nucleus
20°
Angular dispersion as 68% containment radius around known source position
0
5
10
15
20
10 100Energy [MeV]
Ang
ular
di
sper
sion
[deg
]
MEGA
EGRET
The angular resolutionof the MEGA prototypeat 49 MeV is 2x better
than EGRET!
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MEGA Prototype field of view @ 50 MeV: calibration beams to ~80° off-axis
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⎟⎟⎠
⎞⎜⎜⎝
⎛−+⎟⎟
⎠
⎞⎜⎜⎝
⎛=
Ω∂∂ χϕσ 22
22
cossin22 g
i
i
g
i
ge
EE
EE
EEr
Azimuthal distribution: a*cos(2(χ+χ0))+c
Azimuthal scatter angle χ
Beam100% polarized
E
Polarization: Measurement & Simulation
Data
Simulation
MEGA Calibration result:E Modulation [%](MeV) meas. sim.0.7 17± 4 19± 12.0 13± 3 14± 15.0 6± 3 3± 2
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… after MEGA was proposed as a German Small Satellite project (2nd place in 2001), and a balloon flight of the prototype could not be realized, the project was discontinued in 2003 by the MPE directorate.
… since 2005 we started to discuss a renewed effortfor a MeV mission, based on
• new central science cases (among others: nucl.resonance absorption in high-z GRBs, low energy follow up for Fermi sources)
• new detector technology: scintillators, sensors, electronics, simulations
• ESA cosmic vision announcement
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GRIPSGRB Investigation via Polarisation and Spectroscopy
The GRIPS-GRM Simulation Model
Tracker: Double-sided Si-strip detectors
50 kg Silicon, 64 layers with 8x8 wafers (10x10x0.05 cm3), 500 μm pitch, 2.5 keV FWHM energy resolution, 10 keV trigger threshold
Calorimeter: LaBr3
500 kg, 0.5x0.5x2/4/8 cm, 4.4% energy resolution (FWHM) @ 662 keV, 0.5 cm depth resolution in 8 cm crystals, 30 keV trigger threshold
ACS: Plastic scintillator
120 kg BC408, 50 keV average veto threshold
166 cm
Tracker: Double-Sided Si-strip detectors
Calorimeter: LaBr2 with SDD readout
ACS: plastic scintillator
http://www.grips-mission.euGreiner et al., 2009, Exp Astron. 23, 91Zoglauer et al., 2008, New Astron. Rev. 52, 431
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yesyesyesnoyesHygroscopic
?138La decay
138La decay
nonointrinsicradioactivity
371350370560415peak emissionwavelength, nm
~3.6%~2.0%2.6%~7%5.6%energy resolution(FWHM, 662 keV)
~17~25~25~2000~200decay time, ns
6850685440scint.light yield, photons/keV
5.23.795.294.513.67density, g cm-3
CeBr3LaCl3(Ce)LaBr3(Ce)CsI(Tl)NaI(Tl)Scintillator
Investigations of a Calorimeter with improvedenergy resolution and fast timing: old and new Scintillators
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Silicon Drift Detector
scintillation lightAGADE Workshop, 2-5 June 2008 Bernhard Huber, MPE, email: [email protected]
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Scintillators & Test setup
AGADE Workshop, 2-5 June 2008 Bernhard Huber, MPE, email: [email protected]
CsI(Tl) LaBr3:Ce
CeBr3
scintillator
SDD
case
light guide
cold finger
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Energy spectrum of 137Cs measured with LaBr3(Ce) and UV sensitive PMT:resolution at 662 keV ~3.2% (FWHM) (credit: V. Bogomolov, MSU)
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Timing resolution between various scintillators(credit: D. Kolitzus, B. Huber, MPE)
PMT / Scint
radioactive source22Na, 60Co…
194 ± 2LaBr3 vs. CeBr3
182 ± 3BaF2 vs. CeBr3
134 ± 2BaF2 vs. LaBr3
139 ± 2BaF2 vs. BaF2
timingresolution(ps) FWHM
crystals used
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Simulations of GRIPS-GRM:(credit: A. Zoglauer, UCB)
events & background :MGGPOD (Weidenspointner et al., 2005)
reconstruction & instrument fct.MEGALib(Zoglauer, et al., 2006)
Mission:equatorial LEOzenith scanning
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Resolutions and Effective Area
Imaging mode event selections are chosen to optimize the narrow-line point-source sensitivity of the telescope including earth horizon cuts, Compton scatter angle cuts, etc.
(Zoglauer et al, 2008)
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Minimum Detectable Polarization for typical GRB spectra
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GRIPS
GRIPS as a nuclear lineimager/spectrometer
(Zoglauer et al, 2008)
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GRIPS continuum sensitivity: observation time 106 s, ΔE = E
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GRIPS sensitivity in context
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Number of sources that can be detected with the sensitivity of GRIPS
(1 yr exposure) (5 yrs exposure)
Type # total # new
GRBs 660 3300 3300
Blazars 820 950 300
Other AGN 250 300 0?
Pulsars/AXP 60 90 0?
Unidentified 170 230 60
Based on extrapolations of KNOWN source spectra!
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GRIPS (5 years): based on simulated Fermi catalogue.
Effectively based on EGRET sources!
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GRIPS Galctic bulge 511 keV modelled with a …
smooth and
source distribution
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Summary
GRIPS would be a major step forward in nuclear line science, especially all-sky imaging!
GRIPS can be ready for the next ESA Cosmic Vision AO
GRIPS could be a huge leap forward in MeV astronomy for GRBs, cosmic radio-activity, and high-energy sources
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The End
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GRIPS Photopeak energy resolution
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GRIPS γ-line field of view
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How to find high-redshift GRBs?Due to characteristic spectrum of GRB Afterglow:
– Photometry in optical: up to z~6– Photometry in NIR: up to z~12-14 (GROND)– Beyond z~14: not feasible from ground in gamma-rays?!
MISTICI (2005)
z=6.29
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Nuclear Resonance photon absorption ● PDR – Pygmy resonance: produced by the resonance capture of photons on nuclear levels with E of ~ 3-9 MeV
(Axel 1962; Hayward 1977; Van Isacker et al. 1992)
● GDR – Giant Dipole Resonance: process that is crudely described as oscillation of the neutron fluid relative to protons ( not in H, only above He) ~15-25 MeV
(Goldhaber and Teller 1948; Ahrens 1985; Eramzyan et al. 1986)
● Delta-resonance – absorption of photons with an energy ~325 MeV by a nuclei via formation of the Delta-isobar, that leaves a target nuclei and pi-meson(s) in the exit channel (Ahrens 1985; Hagiwara et al. 2002)
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Jochen GreinerFriedrichshafen, 28.5.2008
Interactions of Photons and Atomic Nuclei Interactions of Photons and Atomic Nuclei
We See Effects of (with increasing energy):Excitation of Single Nucleons in Nucleus Potential ("Nuclear Lines")
– hν=Enucl
Collective Excitations of Nucleon Groups ("Pygmi/Giant Resonances")– giant resonances: protons versus neutrons– quasi-deuteron resonances: a pair of proton and neutron– each of these occur in all multipole orders
Excitations of Single Nucleons ("Delta Resonance")…-> Hadron/Quark Phase Transitions
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Jochen GreinerFriedrichshafen, 28.5.2008
Resonance absorption: the effectResonance absorption: the effect
NHfgd=5x1022 cm-2
NHintr=1028 cm-2
z=0
Z=1 (solar)
NHfgd=5x1022 cm-2
NHintr=1028 cm-2
z=0
Z=0.6
NHfgd=1025 cm-2
NHintr=1025 cm-2
z=0
Z=1 (solar)
NHfgd=5x1022 cm-2
NHintr=1028 cm-2
z=0
Z=0.1
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Jochen GreinerFriedrichshafen, 28.5.2008
The brightest COMPTEL/EGRET GRB: The brightest COMPTEL/EGRET GRB: 11σσ result for GRB 930131result for GRB 930131
DR @ z~0.65
Data of Sommer et al. (1994); Ryan et al. (1994); Bromm & Schaefer (1999)
GD
R @
z~0
.65
(Iyudin et al 2005)