Observational Appearance of Black Hole Wind Effect of Electron Scattering

Transcription

1 Observational Appearance of Black Hole Wind Effect of Electron Scattering Kazuyuki OGURA Astronomical Institute Osaka Kyoiku Univ. 29 Jun 2013 Meeting of BH Horizon Univ.

2 Contents Introduction Radiative Transfer about BH wind Our Works Model of the BH wind Result Discussion Summary and Future Works

3 Introduction : Radiative Transfer Limb-Darkening Brighter Than Limb Cooler Darker Than Center Hot

4 Introduction : Radiative Transfer Absorption α ν Radiation η ν Scattering σ ν

5 Introduction : Radiative Transfer 7 arguments! η ν : emissivity ε ν : absorption coefficient χ ν : scattering coefficient ε ν : mass emissivity, κ ν :opacity, σ ν : opacity for scattering

6 Introduction : Radiative Transfer Limb-Darkening of Sun To Observer

7 Introduction : Radiative Transfer Extinction by atomosphere

8 Black Hole Wind Examining BH wind In the relativistic outflows, we should carefully consider the apparent photosphere 1. Apparent Photosphere generally aspherical (even if the flow its self is spherically symmetric) Because the density gradually decrease with radius. 2.Observed quantities in the inertial frame are modified from the emitted one in the comoving frame Due to the relativistic Doppler and aberration effects 3.Apparent Optical Depth is remarkably modified due to the Lorentz-Fitzgerald contraction. (Abramowicz et al. 1991)

9 Black Hole Wind Recently, BH wind has been examined Sumitomo et al.2007, Fukue & Sumitomo 2009, Fukue & Iino2010, Fukue 2009, 2011 Sumitomo T co T obs β=0.2 Apparent Photosphere Relativistic Limb-darkening β=0.8

10 Black Hole Wind Recently, BH wind has been examined Sumitomo et al.2007, Fukue & Sumitomo 2009, Fukue & Iino2010, Fukue 2009, 2011 m dot=10 m dot=100ç Fukue & Sumitomo 2009 γ 4 m dot=1000ç m dot=10000ç Solid : observed Dashed: comving Apparent Luminosity

11 Black Hole Wind Recently, BH wind has been examined Sumitomo et al.2007, Fukue & Sumitomo 2009, Fukue & Iino2010, Fukue 2009, 2011 Fukue & Iino 2010 In the highly relativistic regime, spectra deviate from a blackbody. In particular, reflecting the temperature distribution of the power-law type, the observed spectrum in the highly relativistic regime is roughly expressed as

12 Effect of Scattering Electron Scattering influences the observational properties The temperature in the BH wind is generally high, and electron scattering would play important role. Electron Scattering = coherent or elastic scattering Opacity for Electron scattering κ es =0.4cm 2 /g Last scattering LTE

13 Model of BH wind An Simple model Steady, spherically symmetric wind blows off from the central object. m dot (=Mdot c 2 / L Edd )=const. e dot (=L / L Edd )=const. L edd (=4πcGM/κ es ) :Eddington luminosity 0.8 accelerated wind!! (α=1) R Wind is accelerated in the region, where the optical depth is sufficiently large, to reach a constant terminal speed at infinity.

14 Model of BH wind Density & Temperature Distribution From the continuity equation S S κ es (=0.4cm 2 /g) :Opacity for electron scattering r S (=2GM/c 2 ):Schwarzschild radius γ(=1/(1-β 2 ) 1/2 ):Lorentz factor R hat = R/r S R = (r 2 +z 2 ) 1/2 e dot = L/L edd

15 Model of BH wind Apparent Photosphere Optical depth τ=1 (measured from an observer at infinity) observer κ ff (= ρ 0 T ) :Free-Free opacity z!!=1 In scattering dominated flow, apparent photosphere is Just a last scattering surface!"!!*=1 r

16 Model of BH wind Thermalization Surface Effective optical depth τ*=1 (measured from Apparent photosphere) observer At the thermalization surface, photons are produced as blackbody emission with temperature T 0 (R*) in the comoving flame. They scattered off in the flow keeping their temperatures to reach apparent photosphere. z!"!!*=1 Last scattering!!=1 r

17 Result Shape of Apparent Photosphere there exists a strong limb-darkening effect The radii of the photospheres are larger at far from the z-axis than that at near to the z-axis. This is due to the optical depth effect in a spherically expanding wind, and the relativistic effect. (Abramowicz et al. 1991) Parameters M BH =10 6 M sun, mdot=10000(22m sun /yr), r 0 =10r g, β 0 =0.1 and β =0.3,0.5,0.9

18 Result Shape of Thermalization Surface Very close to a sphere The strong limb-darkening effect would disappear. Parameters M BH =10 6 M sun, mdot=10000(22m sun /yr), r 0 =10r S, β 0 =0.1 and β =0.3,0.5,0.9 The size is very small. photons are thermalized deep inside the wind. In the innermost region, where the flow speed becomes small the flow density quickly increases. The effective optical depth is mainly determined in the inner most region.

19 Result Expected Spectra It can be fit by a single temperature blackbody. The shape of the surface of τ=1 is almost spherical. The comoving spectral can be fit by a single blackbody.

20 Discussion m dot -Dependence In the case of m dot =10 6, , and Parameters M BH =10 6 M sun, r 0 =100r S, β 0 =0.1 and β =0.9 log S! log! For larger value of m dot, the density becomes higher and the radius of the surface of τ*=1 is larger. As the size of the thermalization surface becomes large, the temperature becomes low. On the other hand, the size of the apparent surface also becomes large. As a result, the intensity of spectra becomes high.

21 Discussion r 0 -Dependence In the case of r 0 = 1000,500 and 100r S. Parameters M BH =10 6 M sun, m dot 0 =10 6, β 0 =0.1 and β =0.9 log S! log! For larger value of r 0, the surface of τ*=1 becomes large, therefore the temperature at the surface becomes low.

22 Summary and future Work We have examined the observational properties of BH winds, considering the effect of electron scattering. Apparent photosphere is not spherical, but becomes a non-spherical shape. The thermalization radius is found to be almost spherical. The temperature distributions on the thermalization radius and apparent photosphere are almost uniform, and the expected spectra become a single blackbody type.

23 Summary and future Work We have assumed the gray atmosphere, where the opacity does not depend on frequency. The free-free opacity depends on frequency. Frequency-dependence of opacity should be examined in the future. Inelastic Compton scattering(comptonization) is also important, when the electron temperature is sufficiently high.