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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
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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
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:
OutlineOutline
IntroductionIntroduction
Models — (I) (II)Models — (I) (II)
Discussion and Future WorkDiscussion and Future Work
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
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 :
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)
IntroductionIntroductionWeidenspointner et al. 2006 A&A
IntroductionIntroduction Jean et al. 2006 A&A
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
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
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
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
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)
Models — (I) (II)Models — (I) (II)
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))
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
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
Model (I)Model (I)
electrons
positrons
Electron/Positron Production SpectrumElectron/Positron Production Spectrum
K.S. Cheng et al. 2006K.S. Cheng et al. 2006
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
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
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
Model (I)Model (I)
Guessoum et al. 2005 A&A
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
Model (I)Model (I)
K.S. Cheng et al. 2006K.S. Cheng et al. 2006
ne=1 cm-3
T=2.5 eV
Model (I)Model (I)
K.S. Cheng et al. 2006K.S. Cheng et al. 2006
ne=3*10-3 cm-3
T=100 eV
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
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
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
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
>>Thank You<<>>Thank You<<
Guessoum et al. 2005 A&A
Guessoum et al. 2005 A&A
Guessoum et al. 2005 A&A
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Guessoum et al. 2005 A&A
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
Energy threshold of reactions induced by positrons
Guessoum et al. 2005 A&A
Guessoum et al. 2005 A&A