Broadband SED of Microquasars 微类星体的宽波段光谱能量分布 WU, Xue-Bing （吴学兵） 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 J & H –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)

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 J 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 J

Radio/X-ray correlation in Microquasars Gallo, Fender & Pooley (2003)Xue & Cui (2007)

Understanding the Radio/X-ray correlation (Yuan & Cui 2005, ApJ) Flat slopeSteep slope

2. XTE J & H Both are GBHCs (M BH =8.4~10.8M  for XTE J , 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 H Corbel et al. (2002, 2005) Observed by ATCA

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

Jet Emission

For XTE J : we fixed p = 2.32 and  max = 5.0 × 10 8, the Doppler factor at  = 0.5 and the radius of the emitting region at r = 1 × cm. The only remaining free parameters are B and E tot. 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 = G, E tot /m e c 2 = 1.1×10 16 cm −3 ), (B = G, E tot /m e c 2 = 4.5×10 15 cm −3 ), and (B = G, E tot /m e c 2 = 2.8 × cm −3 ); right: (B = 56.2 G, E tot /m e c 2 =1.0 × cm −3 ), (B = G, E tot /m e c 2 = 1.0 × cm −3 ), and (B = G, E tot /m e c 2 = 2.0×10 16 cm −3 ), respectively.

For H : we fixed p = 2.2,  = 0.8, r = 1 × cm. The remaining free parameters are B,  max and E tot. SED in the low-hard state (left) and the transitional state (right). left: (B = G,  max = 1.4×10 7, E tot /m e c 2 = 7.9×10 15 cm −3 ), (B = G,  max = 1.4×10 8, E tot /m e c 2 = 3.2×10 16 cm −3 ), and (B = G,  max = 4.0 × 10 6, E tot /m e c 2 =8.9 × cm −3 ); right: (B = G,  max = 3.2 × 10 6, E tot /m e c 2 = 1.3 × cm −3 ),(B = G,  max = 1.0 × 10 6, E tot /m e c 2 = 1.1 × cm −3 ),and (B = G,  max = 1.0 × 10 5, E tot /m e c 2 = 4.5 × 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 J (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 Evolution spectral softening (LHS->HSS) and hardening (HSS->LHS) No HSS Can you see the hysteresis? XTE J

H 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 J 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 even during the transitional states. We found evidence for a possible frequency dependence of the correlation.

本组招收博士后 2 名、博士生 2 名 进北大并不难，待遇也不低，出路更不差！ 凡热衷于黑洞、吸积盘、喷流、 X- 射线双星、 类星体和活动星系核的理论和观测研究者均受 欢迎！ 但生性懒惰、不求上进、有不良嗜好者免谈！ 欢迎电邮 和面谈。