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 ==