Broadband SED of Microquasars微类星体的宽波段光谱能量分布

WU, Xue-Bing（吴学兵）wuxb@pku.edu.cn北京大学天文学系

(Dept. of Astronomy, Peking University)

Collaborators: Yongquan Xue & Wei Cui (Purdue); Feng Yuan (SHAO)

“Gang of Four”

Content

• Introduction

• XTE J1550-564 & H 1743-322– Jet emission– Spectral evolution– Radio/X-ray correlation

• Summary

1. Introduction

BH systems at different scale:

Common ingredients: BH, accretion disk, jet, ...

Mirabel (2004) (Microquasars are not quasars, but stellar BHs with jet!)

Different Spectral States of Microquasars

(LHS, HSS, VHS)

Remillard & McClintock (2006)

Remillard & McClintock (2006)

Multi-wavelength study of Microquasars

Radio: Jet

IR: Companion

Opt: Companion

X-ray: Accretion, Jet

Gamma-ray: Jet

(Xue, Wu & Cui 2008, MNRAS, 384,440)

XTE J1550-564

Modelling the broadband spectral energy distribution(SED) of microquasars can be a very effective way to cast light on emission mechanisms !

Yuan, Cui & Narayan (2005, ApJ)

Yuan, Zdziarski, Xue & Wu (2007, ApJ)

XTE J1550-564

Radio/X-ray correlation in Microquasars

Gallo, Fender & Pooley (2003)

0.7R XL L

Xue & Cui (2007)

Understanding the Radio/X-ray correlation

(Yuan & Cui 2005, ApJ)

Flat slopeSteep slope

2. XTE J1550-564 & H 1743-322

• Both are GBHCs (MBH=8.4~10.8M for XTE J1550-564, Orosz et al. 2002)

• Jets have been directly imaged at both radio and X-ray frequencies (Corbel et al. 2002, 2005)

• Jet contribution to the overall SED can be reliably assessed

• Can understand better the contribution of accretion flow to the SED

X-ray Jets

Corbel et al. (2002, 2005)

Observed by Chandra

Radio Jets

H1743-322

Corbel et al. (2002, 2005)

Observed by ATCA

(Xue, Wu & Cui 2008, MNRAS, 384,440)

Jet Emission

For XTE J1550-564:we fixed p = 2.32 and max = 5.0 × 108, the Doppler factor at = 0.5 and the radius of the emitting region at r = 1 × 1010 cm. The only remaining free parameters are B and Etot.

SED in the low-hard state (left) and the transitional state (right). The short dashed, solid, and long-dashed lines show plausible solutions of the synchrotron model, left: (B = 1778.7 G, Etot/mec2 = 1.1×1016 cm−3), (B = 6311.3 G, Etot/mec2 = 4.5×1015 cm−3), and (B = 11223.3 G, Etot/mec2 = 2.8 × 1015 cm−3); right: (B = 56.2 G, Etot/mec2 =1.0 × 1018 cm−3), (B = 891.5 G, Etot/mec2 = 1.0 × 1017 cm−3), and (B = 7945.5 G, Etot/mec2 = 2.0×1016 cm−3), respectively.

For H 1743-322:

we fixed p = 2.2, = 0.8, r = 1 × 1010 cm. The remaining free parameters are B, max and Etot.

SED in the low-hard state (left) and the transitional state (right). left: (B = 7945.5 G, max =

1.4×107, Etot/mec2= 7.9×1015 cm−3), (B = 14129.3 G, max = 1.4×108, Etot/mec2 = 3.2×1016 cm−3),

and (B = 31632.0G, max=4.0 × 106, Etot/mec2=8.9 × 1014 cm−3); right: (B = 199.5 G, max= 3.2

× 106, Etot/mec2 = 1.3 × 1017 cm−3),(B = 1412.6 G, max=1.0 × 106, Etot/mec2= 1.1 × 1016

cm−3),and (B = 8913.2 G, max= 1.0 × 105, Etot/mec2 = 4.5 × 1014 cm−3),respectively.

While the jets can probably account for 100% of the observed radio emission, they contribute little to the observed emission at higher frequencies, when the source is relatively bright.

Where does the bulk of the X-ray emission come from then?==> Originates mostly from accretion flows, as for XTE J1118+480 (Yuan et al. 2005).

With a power law (plus a high-energy rollover for the low-hard state), which approximates an unsaturated Comptonized spectrum, and a multi-color disc component (when needed), we found that the model can adequately fit the data.

Spectral Evolutionspectral softening (LHS->HSS) and hardening (HSS->LHS)

No HSS

Can you see the hysteresis?

XTE J1550-564

H 1743-322

No HSS

No LHS

Can you see the hysteresis?

Radio/X-ray Correlation

simultaneous/contemporaneous radio and X-ray measurements

The best-fitting logarithmic slope was found to be 1.45, 0.94, and 0.89 for radio measurements at 843, 4800, and 8640 MHz, respectively.

XTE J1550-564

Xue & Cui (2007, A&A)

Xue, Wu & Cui (2008, MNRAS)

3. Summary• Physical modeling of the broadband SED of the resolved

components of the jets support a pure synchrotron origin of the observed emission, from radio to X-ray frequencies, in XTE J1550–564 and H 1743–322. The effects of inverse Compton scattering in the jets were found to be negligible.

• Synchrotron radiation from the jets can account for 100% of the observed radio emission but seems to contribute little to the observed X-ray emission from XTE J1550–564 and H 1743–322, when the sources are relatively bright. The bulk of the X-ray emission comes from the accretion flows.

• It is straightforward to define the spectral states based on the shape of SEDs. The presence of a dominant soft (disc) component distinguishes the HSS from transitional states. We presented clear evidence for spectral hysteresis associated with the LHS-to-HSS and HSS-to-LHS transitions and found that the mass accretion rate alone cannot uniquely determine the spectral states.

• There is a general positive correlation between the X-ray and radio fluxes in XTE J1550–564 and H 1743-322 even during the transitional states. We found evidence for a possible frequency dependence of the correlation.

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