The diffuse Xray emission from the Galactic center

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 The diffuse X-ray emission from the Galactic center R. Belmont CESR, Toulouse, France

The diffuse X-ray emission from the Galactic center R. Belmont CESR, Toulouse, France Collaborators: M. Tagger (CEA/APC, France); M. Morris (UCLA, US); M. Muno (Caltech, US) 15/05/07 Simbol-X

Outline • The diffuse emission issue at the Galactic center – Diffuse plasma ?

Outline • The diffuse emission issue at the Galactic center – Diffuse plasma ? – Unresolved discrete point sources ? • Ideas to solve the diffuse plasma paradox – Confinement of the plasma Heavy helium plasma – Heating Viscous friction with dense molecular clouds 15/05/07 Simbol-X

The Galactic Center Region • Central zone: • X-ray view: XR Bulge (25°) c

The Galactic Center Region • Central zone: • X-ray view: XR Bulge (25°) c XR GC (2°) 0 p 10 Strong emission XR disk (50°) • Radio view: Non thermal filaments Vertical B (10 G - 1 m. G) • IR view: La Rosa et al. 2000 The central molecular zone (Morris&Serabyn 1996) Gas condensed in clouds (Bally et al. 87): N~100, R ~ 5 pc, v ~ 100 km s 15/05/07 -1 Simbol-X

The GC X-ray emission Cold component: fluorescence molecular clouds. Soft component: k. BT ~

The GC X-ray emission Cold component: fluorescence molecular clouds. Soft component: k. BT ~ 0. 8 ke. V SN remnants. 6. 4 ke. V 6. 7 ke. V 6. 9 ke. V Hot component: Iron lines non thermal processes ? unresolved point sources ? diffuse plasma (k. T 7 ke. V) ? Hard component ? : Power law ? Muno et al. 2004 At the Galactic center: The diffuse emission (DE) profile is different from that of the resolved point sources (RPS) emission (Suzaku, Koyama et al. 2006). diffuse plasma ? 15/05/07 Simbol-X -- RPS -- DE

Problems with a diffuse plasma ? (Kaneda et al. , 1997) • Energy problem:

Problems with a diffuse plasma ? (Kaneda et al. , 1997) • Energy problem: confinement of the plasma: – cs ~ 1500 km/s ≥ vesc ~ 1100 -1200 km/s the gas escapes – very fast escape: tesc~ 40 000 yr – required power is huge (> 1 SN/3 -300 yr in the central region) • Heating mechanism: – If confined: radiative cooling time = 108 yr – Heating mechanism still needed… 15/05/07 Simbol-X

Confining the plasma… (Belmont et al. 2005) • Weakly collisional plasma: Disjoint study of

Confining the plasma… (Belmont et al. 2005) • Weakly collisional plasma: Disjoint study of the different species in the plasma • Species of different mass have different wills: - As in planetary atmospheres confinement comparison of vth and vesc - 1 -species plasma (+e-): • Only protons are light enough to leave the Galactic plane: Heavy ions ( 4/3 -2) vth� ~600 -750 km s-1 Escape velocity vth~ 1200 km s-1 Protons ( =1/2) vth~ 1300 km s-1 Selective evaporation Natural creation of a heavy He plasma (+metal), confined by gravity 15/05/07 Simbol-X

The hot He plasma vs. Observations • At 8 ke. V, H ad He

The hot He plasma vs. Observations • At 8 ke. V, H ad He are fully ionized no direct diagnostic on the major species • Re-interpretation of spectral data: weaker number densities: n(He) ~ 0. 3 n(H) Similar e- and mass densities Smaller abundances: ([Fe]/[He])He ~ 0. 3 ([Fe]/[He])H Recent observations with Suzaku: [Fe] = 3. 5 [Fe]solar He plasma with solar abundances • Stratification: Heavy ions could sediment ( sed ~ 108 yr) If the stratification is observed (He continuum, Fe line) = evidence for a plasma confined by gravity… The origin of the continuum is uncertain (confusion from the many components). Observation at energy > 7 ke. V (Fe and Ni lines + continuum) with Simbol-X will clarify the spectral components in this spectral region. Spectra at several latitudes may give access to the vertical structure of the plasma for the iron line and the He continuum. 15/05/07 Simbol-X

A possible heating mechanism • Radiative cooling of the confined plasma: • Heating by

A possible heating mechanism • Radiative cooling of the confined plasma: • Heating by the dissipation of the gravitational and kinetic energy of molecular clouds by the strong viscosity (Re ~ 10 -2): (Spitzer 1962) • Effect of the magnetic field (Braginskii 1965): - Inhibited shear viscosity (by 1011 !!) - remaining bulk viscosity l Dissipation efficiency: - Strong viscous coefficient - Subsonic motion: vc < cs < va weak compression - The precise flow structure around clouds must be studied 15/05/07 Simbol-X

The inviscid Alfvén wake: Alfvén wing (Drell et al. 1965, Neubauer 1980) Echo-I in

The inviscid Alfvén wake: Alfvén wing (Drell et al. 1965, Neubauer 1980) Echo-I in the earth magnetosphere Io in the Jovian magnetosphere strong energy flux ! 15/05/07 Simbol-X

Viscous dissipation : Strong outgoing Alfvén flux ! Dissipation by : - Non linear

Viscous dissipation : Strong outgoing Alfvén flux ! Dissipation by : - Non linear effects - Curvature of the field lines For most of the expected values for the magnetic field, dissipation in the Alfvén wings (Belmont&Tagger 2006): - is very efficient - balance the radiative cooling - can account for the observed hot plasma 3 D-MHD numerical simulations with the Zeus code are in progress to validate and extend these results… 15/05/07 Simbol-X

Conclusion • The diffuse plasma issue is particularly interesting at the GC: – Stronger

Conclusion • The diffuse plasma issue is particularly interesting at the GC: – Stronger gravitational potential – High concentration of molecular gas – Vertical structured magnetic field • Its nature is very debated. – Point sources (CVs): not enough of them ? – Diffuse plasma: should not exist since it must escape • The escape of light protons naturally leaves a confined plasma made of He • Its heating can be achieved by the viscous dissipation of the kinetic energy of molecular clouds. 15/05/07 Simbol-X

And Simbol-X… • General input for the GR+GC diffuse emission (previous talks): – Thermal/Non

And Simbol-X… • General input for the GR+GC diffuse emission (previous talks): – Thermal/Non thermal nature • lines + high energy continuum – Diffuse plasma/Discrete sources • High resolution mapping at high energy • Precise source identification and counting at high energy • Specific input for the GC diffuse emission: – Good identification at high energy where the source confusion is high – Look for vertical stratification (thanks to better constrains at high energy on the continuum origin) 15/05/07 Simbol-X