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

Outline ► Introduction ► Positron Sources ► Interstellar Mediums in our galaxy ► Discussion and Future Work

Introduction  production positron rate ~  Positronium fraction ~  Line width ~ (Churazov et al., 2005) (Jean et al., 2006) Board line : Narrow line : (Jean et al., 2006) (J. Knodlseder et al., 2005)

Introduction ► The bulge emission is spherically symmetric and is centered on the galactic center with an extension of ∼ (FWHM) ► Total flux= (Jean et al., 2006)

Introduction ► Problems:  The production of positrons  The galactic map of the annihilation line  The propagation of the positrons between their production sites and annihilation places

Introduction ► Most the propagation of cosmic rays is consider in the system of the diffusion model. ► Diffusion equation:

Spectra of Positrons Energy Loss Charge Exchange with Mediums Radiative Combination with e - Free Annihilation with e - Positronium 2γ2γ 2γ2γ 3γ3γ Synchrotron Radiation Inverse Compton Scattering Bremsstrahlung Loss Ionization and Excitation Loss 511 keV spectrum

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

Novae ► The dominant channels for positron production in Novae are:  13 N  13 C  18 F  18 O  22 Na  22 Ne  26 Al  26 Mg (γ:1.809 MeV)

Supernovae ► The dominant channels for positron production through hydrostatic and explosive nucleosynthesis are:  57 Ni  57 Co  57 Fe (γ:1.37 MeV;122,136keV)  56 Ni  56 Co  56 Fe (γ:150,750,812,847,1238 keV) keV)  44 Ti  44 Sc  44 Ca (γ:1.16 MeV;67.8,78.4 keV) keV)  26 Al  26 Mg (γ:1.809 MeV)

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

Star-Capture by the Black Hole ► The capture of stars by Galactic black hole provides relativistic protons ► Collisions of these protons with surrounding gas result in relativistic positrons with energy E~30 MeV

Star-Capture by the Black Hole electrons positrons Electron/Positron Production Spectrum (K.S. Cheng et al. 2006)

Pulsars (X. Chi et al.,1996)

Light Dark Matter ► The dark matter particles with energy about MeV annihilate into e + e - pairs in the galactic bulge. ► Dark matter halo profile is quite uncertain.

Interstellar Mediums ► The chemical composition of ISM :  Hydrogen: 90.8%  Helium: 9.1%  Heavier elements: 0.12% (K. M. Ferriere, 2001)

Interstellar Mediums ► ISM model (McKee & Ostriker,1977)  2.4% cold phase, n=42 cm -3, T=80K  23% warm neutral phase, n=0.37 cm -3, T=8000K  23% warm ionized phase, n=0.25 cm -3,, T=8000K  52% hot phase, n=3.5*10 -3 cm -3, T= 4.5*10 5 K (N. Guessoum et al., 2005)

Interstellar Mediums ► Berezinkii et al. estimated the average value of the diffusion coefficient  ~10 27 cm 2 s -1 (K.S. Cheng et al.,2006)

Discussion and Future Work ► Study more about the spectra of positron sources ► Calculate the evolution of positrons in the galactic center region by diffusion equation

► C. Boehm et al PRL “ MeV dark matter: Has it been detected? ” “ MeV dark matter: Has it been detected? ” ► K.-W Chan & R. E. Lingenfelter 1993 ApJ “ Positrons from supernovae ” “ Positrons from supernovae ” ► X. Chi et al ApJ “ Pulasr-wind origin of cosmic-ray positrons ” “ Pulasr-wind origin of cosmic-ray positrons ” ► M. Casse et al ApJ “ Hypernovae/Gamma-ray bursts in the galactic center as possible sources of galactic positrons ” “ Hypernovae/Gamma-ray bursts in the galactic center as possible sources of galactic positrons ” ► K. S. Cheng et al ApJ “ Annihilation emission form the galactic black hole ” “ Annihilation emission form the galactic black hole ” ► C. D. Dermer and R. J. Murphy 2001 “ Annihilation radiation in the galaxy ” “ Annihilation radiation in the galaxy ” ► K. M. Ferriere 2001 Review of modern physics “ The interstellar environment of our galaxy ” “ The interstellar environment of our galaxy ” References:

► N. Guessoum et al A&A “ The live and deaths of positrons in the interstellar medium ” “ The live and deaths of positrons in the interstellar medium ” ► P. Jean et al A&A “ Spectral analysis of the galactic e + e - annihilation emission ” “ Spectral analysis of the galactic e + e - annihilation emission ” ► J. Knodlseder et al A&A “ The all-sky distribution of 511 keV electron-positron annihilation emission ” “ The all-sky distribution of 511 keV electron-positron annihilation emission ” ► P. A. Milne et al ApJ “ Positron escape from type Ia supernovae ” “ Positron escape from type Ia supernovae ”

To Be Continued …….

>>Thank You >Thank You<<

Introduction Weidenspointner et al A&A

Introduction Jean et al A&A

Introduction ► Positronium (PS):  It is the bound state of e ＋ and e - Para-PS stateOrtho-PS state

Guessoum et al A&A

Model (II) ► Typical parameters: ► How many MSPs in this region ? P=3 ms B=3*10 8 G  Injection rate

► Dust makes no difference to the 511 keV line profile. (N. Guessoum et al., 2005)