Potential Positron Sources around Galactic Center Department of Physics National Tsing Hua University G.T. Chen 2007/11/29.

Potential Positron Potential Positron Sources around Galactic Sources around Galactic

CenterCenter

Department of PhysicsDepartment of PhysicsNational Tsing Hua UniversityNational Tsing Hua University

G.T. ChenG.T. Chen2007/11/292007/11/29

OutlineOutline

► IntroductionIntroduction►Positron SourcesPositron Sources► Interstellar Mediums in our galaxyInterstellar Mediums in our galaxy►Discussion and Future WorkDiscussion and Future Work

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)

(1.3 0.4)keV (Jean et al., 2006)

Board line :

Narrow line :

(Jean et al., 2006)

(J. Knodlseder et al., 2005)

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

(Jean et al., 2006)

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 of the positrons The propagation of the positrons

between their production sites and between their production sites and annihilation placesannihilation places

IntroductionIntroduction

► Most the propagation of cosmic rays is Most the propagation of cosmic rays is consider in the system of the diffusion consider in the system of the diffusion model.model.

► Diffusion equation:Diffusion equation: , ,k

kk

dEN ND N N Q r E t

t E dt

, , kN N r t E

, ,k kQ r E t A E T t X r

Spectra of Positrons

Energy Loss

Charge Exchange with Mediums

Radiative Combination with e-

Free Annihilation with e-

Positronium

2γ2γ3γ

Synchrotron RadiationInverse Compton ScatteringBremsstrahlung LossIonization and Excitation Loss

511 keV spectrum

Positron SourcesPositron Sources

►Positron productions processesPositron productions processes(C. D. Dermer & R. J. Murphy, 2001)

NovaeNovae

► The dominant channels for positron prodThe dominant channels for positron production in Novae are:uction in Novae are:

1313NN1313C C 1818FF1818O O 2222NaNa2222NeNe 2626AlAl2626Mg (Mg (γ:γ:1.809 MeV)1.809 MeV)

SupernovaeSupernovae

► The dominant channels for positron produThe dominant channels for positron production through hydrostatic and explosive nuction through hydrostatic and explosive nucleosynthesis are:cleosynthesis are:

5757NiNi5757CoCo5757Fe (γ:1.37 MeV;122,136keV)Fe (γ:1.37 MeV;122,136keV) 5656NiNi5656CoCo5656Fe (γ:150,750,812,847,1238 Fe (γ:150,750,812,847,1238

keV)keV) 4444TiTi4444ScSc4444Ca (γ:1.16 MeV;67.8,78.4 Ca (γ:1.16 MeV;67.8,78.4 keV)keV) 2626AlAl2626Mg (Mg (γ:γ:1.809 MeV)1.809 MeV)

Supernovae IaSupernovae Ia (K.-W Chan & R. E. Lingenfelter,1993)

Star-Capture by the Black Star-Capture by the Black HoleHole

► The capture of stars by Galactic black hole proThe capture of stars by Galactic black hole provides relativistic protonsvides relativistic protons

► Collisions of these protons with surrounding gCollisions of these protons with surrounding gas result in relativistic positrons with energy Eas result in relativistic positrons with energy E~30 MeV~30 MeV

e

pp

2

,0

0

Star-Capture by the Black Star-Capture by the Black HoleHole

electrons

positrons

Electron/Positron Production SpectrumElectron/Positron Production Spectrum

(K.S. Cheng et al. 2006)(K.S. Cheng et al. 2006)

PulsarsPulsars

(X. Chi et al.,1996)

Light Dark Matter Light Dark Matter

► The dark matter particles with energy aboThe dark matter particles with energy about 1-100 MeV annihilate into eut 1-100 MeV annihilate into e++ee-- pairs in th pairs in the galactic bulge. e galactic bulge.

► Dark matter halo profile is quite uncertain.Dark matter halo profile is quite uncertain.

Interstellar MediumsInterstellar Mediums

►The chemical composition of ISM :The chemical composition of ISM : Hydrogen: 90.8%Hydrogen: 90.8% Helium: 9.1%Helium: 9.1% Heavier elements: 0.12%Heavier elements: 0.12%

(K. M. Ferriere, 2001)

Interstellar MediumsInterstellar Mediums

► ISM model (McKee & Ostriker,1977)ISM model (McKee & Ostriker,1977) 2.4% cold phase, n=42 cm2.4% cold phase, n=42 cm-3-3, T=80K, T=80K 23% warm neutral phase, n=0.37 cm23% warm neutral phase, n=0.37 cm--

3 3 , T=8000K, T=8000K 23% warm ionized phase, n=0.25 cm23% warm ionized phase, n=0.25 cm-3, -3,

, T=8000K, T=8000K 52% hot phase, n=3.5*1052% hot phase, n=3.5*10-3-3 cm cm-3 -3 , ,

T=T=4.5*104.5*1055KK(N. Guessoum et al., 2005)

Interstellar MediumsInterstellar Mediums

► Berezinkii et al. estimated the average valBerezinkii et al. estimated the average value of the diffusion coefficient ue of the diffusion coefficient ~10~102727 cm cm22ss--

11 (K.S. Cheng et al.,2006)(K.S. Cheng et al.,2006)

, ,kk

k

dEN ND N N Q r E t

t E dt

Discussion and Future WorkDiscussion and Future Work

►Study more about the spectra of Study more about the spectra of positron sources positron sources

►Calculate the evolution of positrons in Calculate the evolution of positrons in the galactic center region by diffusion the galactic center region by diffusion equationequation

► C. Boehm et al. 2004 PRLC. Boehm et al. 2004 PRL ““MeV dark matter: Has it been detected?”MeV dark matter: Has it been detected?”► K.-W Chan & R. E. Lingenfelter 1993 ApJK.-W Chan & R. E. Lingenfelter 1993 ApJ ““Positrons from supernovae”Positrons from supernovae”► X. Chi et al. 1996 ApJX. Chi et al. 1996 ApJ ““Pulasr-wind origin of cosmic-ray positrons”Pulasr-wind origin of cosmic-ray positrons”► M. Casse et al. 2004 ApJM. Casse et al. 2004 ApJ ““Hypernovae/Gamma-ray bursts in the galactic center Hypernovae/Gamma-ray bursts in the galactic center

as possible sources of galactic positrons”as possible sources of galactic positrons”► 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”► C. D. Dermer and R. J. Murphy 2001C. D. Dermer and R. J. Murphy 2001 ““Annihilation radiation in the galaxy”Annihilation radiation in the galaxy”► K. M. Ferriere 2001 Review of modern physicsK. M. Ferriere 2001 Review of modern physics ““The interstellar environment of our galaxy”The interstellar environment of our galaxy”

References:

► N. Guessoum et al. 2005 A&AN. Guessoum et al. 2005 A&A ““The live and deaths of positrons in the interstellar medThe live and deaths of positrons in the interstellar med

ium”ium”► P. Jean et al. 2006 A&AP. Jean et al. 2006 A&A ““Spectral analysis of the galactic eSpectral analysis of the galactic e++ee- - annihilation emissannihilation emiss

ion”ion”► J. Knodlseder et al. 2006 A&AJ. Knodlseder et al. 2006 A&A ““The all-sky distribution of 511 keV electron-positron aThe all-sky distribution of 511 keV electron-positron a

nnihilation emission”nnihilation emission”► P. A. Milne et al. 1999 ApJP. A. Milne et al. 1999 ApJ ““Positron escape from type Ia supernovae”Positron escape from type Ia supernovae”

To Be Continued…….To Be Continued…….

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

IntroductionIntroductionWeidenspointner et al. 2006 A&A

IntroductionIntroduction Jean et al. 2006 A&A

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

Guessoum et al. 2005 A&A

Model (II)Model (II)

► Typical parameters:Typical parameters:

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

37 15 10eN s

P=3 ms

B=3*108 G

Injection rate

5~ 10

42 15 10eN s

► Dust makes no difference to the 511 keV liDust makes no difference to the 511 keV line profile.ne profile. (N. Guessoum et al., 200

5)