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Characteristics of High-EnergyAstronomy TelescopesNuclei in the Cosmos and Techniques of their Astronomical Measurement
Henrike OhlendorfMPE & Uni Würzburg12 Nov. 2008
What is high energy?
soft 120 eV – 12 keVX-rays
hard 12 keV – 250 keV
γ rays 100 keV – 1TeV
Gamma and X-ray spectraoverlapDepends on sourceAstronomy: Often sourceunclear→ Gamma favoured
[xkcd.com/273/]
Problems?
High-energy rays can‘t penetrate the atmosphere
[F. Wirner: Gammaastronomie (particle.astro.kun.nl/hs0607/Gamma.pdf)]
What is a telescope?
„A telescope is an instrument designed forthe observation of remote objects by thecollection of electromagnetic radiation.“
[en.wikipedia.org/wiki/Telescope]
that doesn‘t work with either X- or γ rays
But…
[science.hq.nasa.gov/ kids/imagers/ems/hand.gif]
What is a telescope?
X-rays: Refractive index in e.g. glass ≈1 (cp. VIS: ≈1.5)
[www.whatisnuclear.com/articles/radioactive.png]
[http://www.physik.uni-jena.de/~xro/Lehre/ExphysikSS/Fernrohr.png (2)]
that doesn‘t work with either X- or γ rays
But…
[science.hq.nasa.gov/ kids/imagers/ems/hand.gif]
What is a telescope?
X-rays: Refractive index in e.g. glass ≈1 (cp. VIS: ≈1.5)
[www.whatisnuclear.com/articles/radioactive.png]
So how to build a telescope?[http://www.physik.uni-jena.de/~xro/Lehre/ExphysikSS/Fernrohr.png (2)]
What is a telescope?
„A telescope […] is a system characterizedby its aperture and its detector.“
[von Ballmoos]
„While the aperture defines the method of collecting photons […] the detector
measures their properties […].“[von Ballmoos]
→ Find solutions that do not depend on refraction
If we can‘t use refraction, let‘s try reflection!
Reflection at large angles does not work either
[www.astrofotografie.org/images/maksutov.jpg]
Grazing incidence
θ1
θ2 1
2
2
1
sinsin
nn
θθ
=
n1=nvac=1
n2<1
Snell‘s law:
Grazing incidence
θ1
θ2 1
2
2
1
sinsin
nn
θθ
= 21sin nθ =⇒
n1=nvac=1
n2<1
Snell‘s law:
=90°
21cos nθ =⇒1
2
2
1
coscos
nn
θθ
=
Grazing incidence
n2 1 ⇒ cos θ1 1 ⇒ θ1<<1The shorter the wavelength the smaller θ1gets
n1=nvac=1
n2<1
θ1 θ2
Snell‘s law:
⇒ Grazing incidence leads to total reflection
Wolter mirrors
Wolter-Igeometryusually usedin x-rayastronomy
[chandra.harvard.edu/graphics/resources/illustrations/grazing2D-72.gif]
[imagine.gsfc.nasa.gov/docs/science/how_l2/xtelescopes_systems.html (2)]
Chandra
[chandra.harvard.edu/graphics/resources/illustrations/chandra_space.jpg][chandra.harvard.edu/graphics/resources/illustrations/chandra_space.jpg]
Chandra
Iridium-coated Wolter-I mirrors, highlypolishedWatched by CCD array and camera of micro-channel plates in focal plane
[chandra.harvard.edu/graphics/resources/illustrations/chandra_space.jpg][chandra.harvard.edu/graphics/resources/illustrations/chandra_space.jpg]
[chandra.harvard.edu/graphics/resources/illustrations/cxcmirrors.jpgl]
MCPs
Glass tubesElectrons cause avalanchePosition information via crossed grid of wires below MCP (Chandra) or otherwise
[Wiza (2)]
XMM-Newton
[xmm.esac.esa.int/external/xmm_science/gallery/images/XMM.jpg]
XMM-Newton
Goal: Good performance at high energies(~7 keV)
Small grazing angle (~30´)High focal length (7.5 m)
⇒ Wolter mirrorsdon‘t work at high energies
[xmm.esac.esa.int/external/xmm_user_support/documentation/technical/Mirrors/index.shtml] [xmm.esac.esa.int/external/xmm_science/gallery/images/XMM.jpg]
[www.awi.de/fileadmin/user_upload/News/Press_Releases/2008/2._Quartal/0000_HummerHelg_USchilling_out_p.jpg]
Lobster-eye telescopes
Similar to MCPSurfaces bent to achieve focussingFocussing through reflections at grazing angles
[http://www.src.le.ac.uk/projects/lobster/raypath.jpg]
[http://www.src.le.ac.uk/projects/lobster/lobstereye1.jpg]
Lobster-ISS
[www.rssd.esa.int/index.php?project=LOBSTER&page=index]
Lobster-ISS
Planned ISS/Columbus mission (as per 2005)Using lobster eye optics and „microwell“detectors
[www.rssd.esa.int/index.php?project=LOBSTER&page=index]
Microwell detectorLarge array of small (~400 μm) proportional countersPC provide energy informationPositional information via position of PC
Crystal reflection
X-ray diffraction on crystal planes
Bragg (surface) or Laue (inner planes) reflection
Laue reflection works for gamma rays
[von Ballmoos (2)]
Laue lenses
Narrow bandpass: Each ring with different [hkl] to focus similar energiesBroad bandpass: Each ring uses same[hkl], focusses slightly different energies
[Barriere et al.]
MAX (projected [2006])Two satellites at 86 m distance (focal length)Copper and germanium crystaltiles
Germanium detectors
Ge diode under reverse-biasvoltageMost gamma rays getstopped, produce electrons(photoelectric effect)Photoelectron carries gammaenergy, creates furtherelectron-hole pairsNumber of e/h pairs isproportional to incidentenergy
Radiation damage: increased numberof e/h pairs⇒ annealing
[www.internaldosimetry.com/courses/introdosimetry/images/Photelect.JPG]
see: Attenuation coefficients
SPI
[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=30843]
SPI
Hexagonal array of 19 Ge detectorsTotal detection area 508 cm2
Narrow bandgap: Reduce thermal excitation ⇒ Mechanical coolingVarious background rejection systems
Uses coded mask technique
[http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=30843][Vedrenne et al.]
Coded mask
Mask casts shadow whichtells about the object angleSeveral sources: Images interfere ⇒ processingneeded
[Vedrenne et al.]
Detector[adapted fromisdc.unige.ch/Images/medium/codedMask2.gif]
[imagine.gsfc.nasa.gov/Images/features/exhibit/coded_aperture.jpg]
Scintillators
Deposited energyraises electronicstate (~0.1 ps)Deexcitation of vibrational state(~10 ns)Decay and emission of photon
⇒ Fluorescence
E
R
vibrational states
electronic states
[adapted from www.nyu.edu/classes/tuckerman/honors.chem/lectures/lecture_18/BO_surfaces_crude.png, following von Ballmoos]
Scintillators
Creation of e/h pairsHoles ionize activatorElectrons recombineActivator deexcites(~10-7 s)
Valence band
Conduction band
Activator
[following von Ballmoos]
IBIS-PICsITCsI(Tl) bars, 150 keV – 10 MeV
IBIS-ISGRICdTe (semicond.), 15 keV – 1 MeV
⇒ together: Compton telescope
Scintillators
Creation of e/h pairsHoles ionize activatorElectrons recombineActivator deexcites(~10-7 s)
Valence band
Conduction band
Activator
[following von Ballmoos]
Compton telescopes
Incident γ ray compton-scatters in upperdetector layerGets absorbed in lowerCompton equation:
Incident ray can bebackprojected into a conePositional information: overlapping cones
⎟⎟⎠
⎞⎜⎜⎝
⎛+
−−=212
2 111ΦcosEEE
cme
[heseweb.nrl.navy.mil/gamma/detector/compton/compton.gif]
[www.llnl.gov/str/May06/gifs/Fabris5.jpg] see: Attenuation coefficients
see: Compton effect
COMPTEL
[heasarc.gsfc.nasa.gov/docs/cgro/images/epo/gallery/cgro/cartoon_gro.jpg]
COMPTEL
First compton telescope on a satelliteUpper layer: liquid scintillatorLower layer: NaI(Tl) (distance: 1.5 m)Both viewed by photomultiplier tubes(8/7 per detector element)
[heasarc.gsfc.nasa.gov/docs/cgro/images/epo/gallery/cgro/cartoon_gro.jpg]
LAT
[fermi.gsfc.nasa.gov/public/resources/images/spacecraft_07_bkgd.html]
LAT
Tracker: Silicon-stripmodulesTwo-dimensional positionalinformation by criss-crossing3D: 19 pairs of layersCalorimeter: CsI(Tl) scintillator
[fermi.gsfc.nasa.gov/public/resources/images/spacecraft_07_bkgd.html]
[fermi.gsfc.nasa.gov/public/resources/images/LAT_cutaway.jpg]
see: Attenuation coefficients
Čerenkov telescopes
Problem: Nearly every γ quant will hit a molecule in the atmosphere
Use that to advantage: Pair production…, bremsstrahlung, pair production, …
⇒ Particle shower
⇒ Very fast charged particles[www.es.mq.edu.au/geology/USRG/bilder/cosmic.jpg]see: Attenuation coefficients
Čerenkov effect
[http://www.smh.com.au/news/national/lucas-heights-reactor-fires-up/ 2006/11/03/1162340039497.html]
[http://hep.ucsb.edu/people/hnn/ cerenkov.jpg]
Charged particle fasterthan light in a mediumBlue light is emitted in shape of a cone
Compare: Cyclist passingthrough a puddle
Čerenkov effect
Charged particle polarizes mediumDepolarisation by emission of a sphericalwave after short relaxation time (<10-11s)Spherical waves travel outwardConstructive interference only on a cone
see: Cerenkov effect II
Čerenkov telescopes
Čerenkovcone reaches earth, diameter ~250 mEffective collection area ~105 m2
[F. Wirner: Gammaastronomie (particle.astro.kun.nl/hs0607/Gamma.pdf)]
Čerenkov telescopes
Čerenkovcone reaches earth, diameter ~250 mEffective collection area ~105 m2
[F. Wirner: Gammaastronomie (particle.astro.kun.nl/hs0607/Gamma.pdf)]
But why can‘t I see it?extremely short flash(some 10-9 s)very faint (~100 ph m-2)
Čerenkov telescopes
Advantage: Much larger collection areathan satellites
Hard γ ray flux is small (≈1 ph m-2 yr-1)Higher energies can be seenSpace instruments limited to below ~10 GeV
Imaging Atmospheric Cherenkov Telescopes
MAGIC
[magic.mppmu.mpg.de/gallery/pictures/tn/img_5826.jpg.html]
MAGIC
17 m diameter, ~230 m2 (SPI: ~0.05 m2)940 heated aluminium mirror segmentsDetector: 576 photomultipliers, hexagonallyarrangedLa Palma: Perfectly dark nights (aroundnew moon)
[magic.mppmu.mpg.de/gallery/pictures/tn/img_5826.jpg.html]
MAGIC
If the telescope is pointed on the source, a photon should hit it parallel to its axisTrace will point to the centre (or slightlybeside it)
[adapted from Cauet/Brambach]
[Cauet/Brambach]
MAGIC
Muonic and hadronic showers can bedistinguished
[Cauet/Brambach (2)]
Localisation
Better localisation of sources: Use morethan one telescope
MAGIC & MAGIC-II, La Palma, since2004/2008H.E.S.S. (4 telescopes), Khomas upland(Namibia), since 2002HEGRA (5 telescopes), La Palma, 1992-2002CANGAROO-III (4 telescopes), Woomera(Australia), since 2004 (CANGAROO since1992)VERITAS (4 telescopes), Tucson (USA), since2007
H.E.S.S.
[www.mpi-hd.mpg.de/hfm/HESS/pages/about/pictures/HESS_IMG/pages/image041.html]
Overview
[G. Kanbach/R. Diehl]
Anyquestions?
Sources & LiteratureJ. R. P. Angel: Lobster Eyes as X-ray Telescopes; The Astrophysical Journal, Vol. 233, 364 (1979)P. von Ballmoos: Instruments for Nuclear Astrophysics in M. Guedel, R. Walter (ed.): High-Energy SpectroscopicAstrophysics. Saas-Fee Advanced Course 30, 2000; Springer-Verlag, Berlin, Heidelberg 2005N. Barriere et al.: MAX: Development of a Laue diffraction lens for nuclear astrophysics; Nuclear Instruments and Methods in Physics Research Section A, Vol. 567, 333 (2006)C. Cauet, T. Brambach: Physikalisches Fortgeschrittenenpraktikum: MAGIC-Datenauswertung. Anleitung zur Versuchsdurchführung, Universität Dortmund 2007P. A. Charles, F. D. Seward: Exploring the X-ray Universe; Cambridge University Press, Cambridge 1995R. Diehl: Observational High-Energy Astrophysics: Instruments: Cosmic Rays, Gamma-Rays; Lecture Notes, TU München2008heasarc.gsfc.nasa.gov/docs/cgro/comptel/compteldesc.html (COMPTEL)W. Hofmann: Blaue Blitze aus dem Kosmos – Das HESS-Experiment (www.weltderphysik.de/de/242.php)icrhp9.icrr.u-tokyo.ac.jp/c-iii.html (CANGAROO)G. Kanbach et al.: Development and Calibration of the tracking Compton/Pair telescope MEGA; Nuclear Instruments and Methods in Physics Research Section A, Vol. 541, 310 (2005)D. H. Lorenzen: MAGIC macht‘s möglich: Stimmen zum Gammastrahlen-Auge auf La Palma(www.weltderphysik.de/de/240.php)magic.mppmu.mpg.de (MAGIC)„Magie“ auf dem Gipfel; MaxPlanckForschung 4/2003A. Moralejo for the MAGIC collaboration: The MAGIC telescope for gamma-ray astronomy above 30 GeV; Memorie dellaSocietà Astronomica Italiana, Vol 75, 232 (2004)J. van Paradijs, J. A. M. Bleeker (ed.): X-Ray Spectroscopy in Astrophysics. EADN School X Amsterdam, The Netherlands1997; Springer-Verlag, Berlin, Heidelberg 1999V. Schönfelder et al.: Instrument description and performance of the imaging gamma-ray telescope COMPTEL aboard theCompton Gamma-Ray Observatory; The Astrophysical Journal Supplement Series Vol. 86, 657 (1993)R. K. Smither et al.: Review of Crystal Diffraction and its Application to Focusing Energetic Gamma Rays in L. Bassani, G. di Cocco (ed.): Imaging in High Energy Astronomy; Kluwer Academic Publishers, Dordrecht 1995G. Vedrenne et al.: SPI: The spectrometer aboard INTEGRAL; Astronomy & Astrophysics 411, L63–L70 (2003)veritas.adlerplanetarium.org (VERITAS)J.L. Wiza: Microchannel Plate Detectors; Nuclear Instruments and Methods, Vol. 162, 587 (1979)www.mpi-hd.mpg.de/hfm/CT/CT.html (HEGRA)www.mpi-hd.mpg.de/hfm/HESS/ (H.E.S.S.)www.src.le.ac.uk/projects/lobster/ (LOBSTER-ISS)
Attenuation coefficients
Total
Compton Pair prod. (nuclear)
Pair prod. (electronic)
Photoel. Effect
Ge
[Data: NIST Photon Cross Section Database (physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html)]
Compton effect
[adapted fromwww.physicsmasterclasses.org/exercises/bonn2/de/images/compton.jpg]
cνh ′
cνh
mvp =
νν ′≈Assume:
2sin
21 θ
cνhmv =
( )
2
222
2
2
2
2sin2
2sin2
21
2121
mc
θνh
m
θcνh
mmv
mvνhνh
=
⎟⎠⎞
⎜⎝⎛
=
=
=′−
νν
θmc
hννν
112
sin2 222
−′
≈
=′−
( )θmch
θmc
hλλλ
cos1
2sin2Δ 2
−=
=−′=
Particle travels with speed vShockwave travels with speed of light c/n
Opening angle allows to determine v
Čerenkov effect II
medcncv =>
cvβ = :Def.
nβctβnctθ 1/cos ==
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