The 511 keV Annihilation Emission From The Galactic Center

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The 511 keV The 511 keV Annihilation Annihilation Emission From The Emission From The Galactic Center Galactic Center Department of Physics Department of Physics National Tsing Hua University National Tsing Hua University G.T. Chen G.T. Chen 2007/1/2 2007/1/2

description

The 511 keV Annihilation Emission From The Galactic Center. Department of Physics National Tsing Hua University G.T. Chen 2007/1/2. References:. K.S. Cheng et al. 2006 ApJ “ Annihilation emission form the galactic black hole ” W. Wang et al. 2006 A&A - PowerPoint PPT Presentation

Transcript of The 511 keV Annihilation Emission From The Galactic Center

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The 511 keV Annihilation The 511 keV Annihilation Emission From The Emission From The

Galactic CenterGalactic Center

Department of PhysicsDepartment of PhysicsNational Tsing Hua UniversityNational Tsing Hua University

G.T. ChenG.T. Chen2007/1/22007/1/2

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K.S. Cheng et al. 2006 ApJK.S. Cheng et al. 2006 ApJ ““Annihilation emission form the galactic black hole”Annihilation emission form the galactic black hole” W. Wang et al. 2006 A&AW. Wang et al. 2006 A&A ““Could electron-positron annihilation lines in the galactic center rCould electron-positron annihilation lines in the galactic center r

esult from pulsar winds ? ”esult from pulsar winds ? ” W. Wang 2005 astro-ph/0510461W. Wang 2005 astro-ph/0510461 ““Millisecond pulsar population in the galactic center and high enMillisecond pulsar population in the galactic center and high en

ergy contributions”ergy contributions” N. Guessoum et al. 2005 A&AN. Guessoum et al. 2005 A&A ““The live and deaths of positrons in the interstellar medium”The live and deaths of positrons in the interstellar medium” Jean et al. 2006 A&AJean et al. 2006 A&A ““Spectral analysis of the galactic eSpectral analysis of the galactic e++ee- - annihilation emission”annihilation emission” Knodlseder et al. 2006 A&AKnodlseder et al. 2006 A&A ““The all-sky distribution of 511 keV electron-positron annihilation The all-sky distribution of 511 keV electron-positron annihilation

emission”emission”

References:

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OutlineOutline

IntroductionIntroduction

Models — (I) (II)Models — (I) (II)

Discussion and Future WorkDiscussion and Future Work

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IntroductionIntroduction

Radiation of eRadiation of e++-e-e-- annihilation from the annihilation from the galactic center was first reported in 19galactic center was first reported in 1972 72

Recently, we have the observation datRecently, we have the observation data by SPI of the INTEGRAL a by SPI of the INTEGRAL

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IntroductionIntroduction

The bulge emission is spherically The bulge emission is spherically symmetric and is centered on the symmetric and is centered on the galactic center with an extension of galactic center with an extension of ∼ ∼ 5500-8-800 ( (FWHMFWHM))

Total flux=Total flux= 3 21.09 0.04 10 /photons s cm

3 2(0.35 0.11) 10 /photons s cm

3 2(0.72 0.12) 10 /photons s cm (Jean et al. 2006 A&A)

Board line :

Narrow line :

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IntroductionIntroduction

43 110 s

(5.4 1.2)keV

0.967 0.022

production positron rate ~

Positronium fraction ~

2.37 0.25keVLine width ~ (Churazov et al. 2005 MNRAS)

(1.3 0.4)keV (Jean et al. 2006 A&A)

Board line :

Narrow line :

(Jean et al. 2006 A&A)

(J. Knodlseder et al. 2005 A&A)

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IntroductionIntroductionWeidenspointner et al. 2006 A&A

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IntroductionIntroduction Jean et al. 2006 A&A

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IntroductionIntroduction

Problems:Problems: The production of positronsThe production of positrons The galactic map of the annihilation The galactic map of the annihilation

line line The propagation/evolution of the The propagation/evolution of the

positrons between their production positrons between their production sites and annihilation placessites and annihilation places

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IntroductionIntroduction

Positrons can be produced by:Positrons can be produced by: ββ++ decay decay Pion decayPion decay Pair production (ePair production (e ++ - e- e-- ) through photo ) through photo

n-photon interactionsn-photon interactions Pair production by the interaction of an Pair production by the interaction of an

ee-- with a strong magnetic field with a strong magnetic field

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IntroductionIntroduction

Positronium (PS):Positronium (PS): It is the bound state of eIt is the bound state of e ++ and eand e- -

Para-PS state Ortho-PS state

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IntroductionIntroduction

In order to determine the overall spectrum In order to determine the overall spectrum of the line produced by galactic positrons, of the line produced by galactic positrons, we must consider the model of ISM we must consider the model of ISM distributions, temperatures and ionization distributions, temperatures and ionization of the gases and dusts.of the gases and dusts.

Taking all the physical information Taking all the physical information (processes, cross sections, line widths, gas (processes, cross sections, line widths, gas distributions, etc.) into account , we can distributions, etc.) into account , we can reproduce the observational datareproduce the observational data

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IntroductionIntroduction The ISMs in the galactic centerThe ISMs in the galactic center Cold neutral component (n=10 cmCold neutral component (n=10 cm-3-3, T=80K), T=80K) Warm neutral component (n=0.3 cmWarm neutral component (n=0.3 cm-3-3, T=8000K), T=8000K) Warm ionized component (n=0.17 cmWarm ionized component (n=0.17 cm-3-3, T=8000K), T=8000K) Hot component (n=3*10Hot component (n=3*10-3-3 cm cm-3-3, T=4.5*10, T=4.5*1055K)K)

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Models — (I) (II)Models — (I) (II)

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ModelsModels

…………………… Star accretion by central supermassive bStar accretion by central supermassive b

lack hole (Model I)lack hole (Model I) ((K.S. Cheng et al. 2006 ApJK.S. Cheng et al. 2006 ApJ ) ) Millisecond pulsars in the galactic bulge Millisecond pulsars in the galactic bulge

region (Model II)region (Model II) ((W. Wang et al. 2006 A&AW. Wang et al. 2006 A&A))

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Model (I)Model (I)

The assumptions in this model:The assumptions in this model: The rate of production of positrons~The rate of production of positrons~ If positrons are produced via p-p collisions, thIf positrons are produced via p-p collisions, th

e total energy of protons must not exceed e total energy of protons must not exceed The spatial distribution of positrons should exThe spatial distribution of positrons should ex

tend over a region with angular radius 5tend over a region with angular radius 500-8-800 ar around GC when they cool down to thermal eneround GC when they cool down to thermal energies gies

43 110 s

53 5410 10 ergs

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Model (I)Model (I)

The capture of stars by Galactic black hole pThe capture of stars by Galactic black hole provides relativistic protonsrovides relativistic protons

Collisions of these protons with surrounding Collisions of these protons with surrounding gas result in relativistic positrons with energgas result in relativistic positrons with energy E>30 MeVy E>30 MeV

e

pp

2

,0

0

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Model (I)Model (I)

electrons

positrons

Electron/Positron Production SpectrumElectron/Positron Production Spectrum

K.S. Cheng et al. 2006K.S. Cheng et al. 2006

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Model (I)Model (I)

Consider the interactions of positrons aConsider the interactions of positrons and gases ---ionization loss+ synchrotron nd gases ---ionization loss+ synchrotron +inverse Compton loss +bremsstrahlung +inverse Compton loss +bremsstrahlung loss , we can describe the evolution of thloss , we can describe the evolution of the positrons spectrum from relativistic to e positrons spectrum from relativistic to thermal energiesthermal energies

2

0

1 ( )( , ) ( ) ( )an ce

e

vnf f pf q p r A p B p f

t p p p

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Model (I)Model (I)

K.S. Cheng et al. 2006K.S. Cheng et al. 2006

ne=1 cm-3

T=2.5 eV

ep p m kT

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Model (I)Model (I)

Later Coulomb collision continue to Later Coulomb collision continue to form the equilibrium distribution and form the equilibrium distribution and accumulate positrons in the thermal accumulate positrons in the thermal energy range, then these thermal energy range, then these thermal positrons decrease because of positrons decrease because of annihilationannihilation

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Model (I)Model (I)

Guessoum et al. 2005 A&A

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Model (I)Model (I)

In this case, they assume the In this case, they assume the annihilation spectrum is caused by annihilation spectrum is caused by in-flight annihilation with ein-flight annihilation with e-- and and charge exchange with Hcharge exchange with H

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Model (I)Model (I)

K.S. Cheng et al. 2006K.S. Cheng et al. 2006

ne=1 cm-3

T=2.5 eV

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Model (I)Model (I)

K.S. Cheng et al. 2006K.S. Cheng et al. 2006

ne=3*10-3 cm-3

T=100 eV

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Model (II)Model (II)

There possibly exists a population of millisecoThere possibly exists a population of millisecond pulsars (MSPs) in the Galactic center region.nd pulsars (MSPs) in the Galactic center region.

MSPs could emit GeV gamma-rays through synMSPs could emit GeV gamma-rays through synchrotron-curvature radiation as predicted by ochrotron-curvature radiation as predicted by outer gap modelsuter gap models

MSP winds provide good candidates for the eMSP winds provide good candidates for the e++ - e- e-- sources in the Galactic center sources in the Galactic center

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Model (II)Model (II)

They consider the eThey consider the e ++ - e- e-- pair productio pair production occurs in the pulsar outer-magnetospn occurs in the pulsar outer-magnetosphere regionhere region

MSP winds are positron sources which rMSP winds are positron sources which result from pair cascade near neutron esult from pair cascade near neutron star surfacestar surface

MSPs are active near Hubble time, so thMSPs are active near Hubble time, so they are continuous positron injecting soey are continuous positron injecting sourcesurces

e

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Model (II)Model (II)

Typical parameters:Typical parameters:

How many MSPs in this region ?How many MSPs in this region ?

37 15 10e

N s

P=3 ms

B=3*108 G

Injection rate

5~10

42 15 10e

N s

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Discussion & Future WorkDiscussion & Future Work

Study much details in the model(I)Study much details in the model(I) Apply some tools learning from model(I) Apply some tools learning from model(I)

to MSPs modelto MSPs model

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>>Thank You<<>>Thank You<<

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Guessoum et al. 2005 A&A

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Guessoum et al. 2005 A&A

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Guessoum et al. 2005 A&A

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Guessoum et al. 2005 A&A

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Annihilation rel. electrons

Ionization loss of positrons

Ionization loss of electrons Syn.+Inverse Compton rel.

electrons

K.S. Cheng et al. 2006K.S. Cheng et al. 2006

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Energy threshold of reactions induced by positrons

Guessoum et al. 2005 A&A

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Guessoum et al. 2005 A&A