1. Toward understanding the X-ray emission of the hard state of XTE J1550-564
Feng Yuan
Collaborators: X. B. Wu (PKU), Y.Q. Xue (Purdue) , A. A. Zdziarski (CAMK)
CAS Meeting, 2005, USTC

2. Outline Brief introduction to black hole X-ray binaries
Luminous hot accretion flow (LHAF)
Explaining the X-ray origin of luminous hard states with an LHAF
An evidence against the jet origin of the X-ray emission in hard states

3. Five states (I) Quiescent state: Low/Hard state
Extremely weak, L_x=10^ ^33.5erg/s
Nonthermal spectrum, with \Gamma= (may depend on the orbital period)
Low/Hard state
The spectrum is dominated(>80% at 2-20 keV) by a power-law spectrum
The photon index is 1.5<\Gamma<2.1
Power continuum is strong (0.1<r<0.3)
Strong radio emission

4. Five States (II) High/soft state
the disk-flux fraction is above 75%(2-20keV)
The PDS shows no QPO or rms<<1%
Power continuum is weak: r<0.06
No radio
SPL or Very high state and intermediate state
A power-law X-ray spectrum with \Gamma>2.4 is present
QPO is present while the power-law contributes more than 20% of the total flux in 2-20 keV; or
No QPO while the power-law contributes more than 50% of the total flux
No radio, but associated with explosive formation of radio jet

5. Five States: spectrum
Zdziarski. & Gierliński 2004

6. Theoretical models
Esin, McClintock & Narayan 1997, ApJ

7. The Origin of the X-ray emission of Luminous Hard States: ADAF ?
Corresponding accretion rates:
The largest luminosity of ADAF: 4%L_Edd
The X-ray luminosity of some luminous hard states are higher than 4%L_Edd:
XTE J : 10% & 20% L_Edd
GX339-4: 30% L_Edd

8. ADAF and Its Critical Accretion Rate
The energy equation of ions in ADAFs:
For a typical ADAF (i.e., ), we have:
Since q- increases faster than q+ and qadv with increasing accretion rate, there exists a critical accretion rate of ADAFs, determined by (Narayan, Mahadevan & Quataert 1998):
So advection is a cooling term
Self-similar solution of ADAF

9. The dynamics of LHAFs: Basic Physics
What will happen above the critical rate of ADAF?
Originally people think no hot solution exists; but this is not true
The energy equation of accretion flow:
since:
So we have:

10. The dynamics of LHAFs: Basic Physics
An ADAF is hot because
so the flow remains hot if it starts out hot.
When , up to another critical rate determined by
We still have: 
So again the flow will be hot if it starts out hot, i.e., a new hot
accretion solution (LHAFs) exists between

11. Properties of LHAFs Using the self-similar scaling law:
LHAF is more luminous than ADAFs since it corresponds to higher accretion rates and efficiency.
The entropy decreases with the decreasing radii. It is the converted entropy together with the viscous dissipation that balance the radiation of the accretion flow.
Since the energy advection term is negative, it plays a heating role in the Euler point of view.
The dynamics of LHAFs is similar to the cooling flow and spherical accretion flow.

12. Summary: four accretion solutions: accretion rates and efficiency
Cool series
Hot series
Yuan 2001, MNRAS

13. Modeling the 2000 outburst of XTE J1550-564
6% LEdd
3%LEdd
1%LEdd
Yuan, Zdziarski, Xue & Wu 2007, ApJ

14. The advection factor of the three solutions
LHAF
From Yuan, Zdziarski, Xue & Wu 2007, ApJ

15. The calculated temperature vs. the E-folding energy of the spectra
Yuan, Zdziarski, Xue & Wu 2007, ApJ
Temperature profiles of the three solutions; the three dots show the
E-folding energy of the three X-ray spectra shown in a previous figure.

16. The optical and X-ray light curves of XTE J1550-564 during its 2000 outburst.
Secondary maxima
No maximum in the X-ray!
Jain et al. 2001, ApJ

17. Secondary Maximum: the contribution of the jet
Jet emission
Yuan, Zdziarski, Xue & Wu 2007

18. Thank you!