The Hard X-ray Spectral Evolution in XRBs, AGNs and ULXs

We explore the relationship between the hard X-ray photon index $\Gamma$ and the Eddington ratio (\xi=L_{X}(0.5-25 keV)/L_{Edd}) in six XRBs. We find that different XRBs follow different anti-correlations between $\Gamma$ and $\xi$ when $\xi$ is less than a critical value, while they follow the same positive correlation when $\xi$ is larger than the critical value. This anti-correlation and positive correlation are also found in LLAGNs and QSOs respectively, and the anti-correlation and positive correlation of different XRBs roughly converge to the same point ($\log \xi=-2.1, \Gamma=1.5$), which may correspond to the accretion mode transition, since that the anti-correlation and positive correlation are consistent with the prediction of ADAFs and standard disk/corona system respectively. The traditional low/hard state are divided into two parts by the cross point $\log \xi\sim-2.1$, i.e., faint-hard state in the anti-correlation part and bright-hard state in the positive correlation part. The accretion process in the bright-hard state may be still the standard accretion disk as that in the high/soft state, which is consistent with that both the cold disk component and broad Fe K emission line are observed in some bright-hard state of XRBs. The ADAF is only important in the faint-hard state XRBs. Motivated by the similarities of the state transition and timing properties of the ULXs to that of XRBs, we then constrain the BH masses for seven luminous ULXs assuming that their X-ray spectral evolution is similar to that of XRBs. We find that the BH masses of these seven ULXs are around $10^{4}M_sun$, which are typical intermediate mass BHs (IMBHs). Our results are roughly consistent with the BH masses constrained from the model fitting with a multi-color disk and/or the timing properties(e.g., QPO and break frequency).Comment: 5 pages, 1 figure, accepted for pulication in Proceeding of SCience, VII Microquasar Workshop, 2008 September 1-5, Foca, Turke

Possible Origin of Radio Emission from Nonthermal Electrons in Hot Accretion Flows for Low-Luminosity Active Galactic Nuclei

The two components of radio emission, above and below 86 GHz respectively, from the Galactic center source-Sgr A* can be naturally explained by the hybrid of thermal and nonthermal electrons in hot accretion flows (e.g., radiatively inefficient accretion flow, RIAF, e.g., Yuan et al. 2003). We further apply this model to a sample of nearby low-luminosity active galactic nuclei (LLAGNs), which are also believed to be powered by the RIAF. We selected the LLAGNs with only compact radio cores according to the high-resolution radio observations, and the sources observed with jets or jet-like features are excluded. We find that the radio emission of LLAGNs is severely underpredicted by pure RIAF model, and can be naturally explained by the RIAF model with a hybrid electron population consisting of both thermal and nonthermal particles. Our model can roughly reproduce the observed anti-correlation between the mass-corrected radio loudness and Eddington ratio for the LLAGNs in our sample. We further model the spectral energy distributions of each source in our sample, and find that roughly all sources can be well fitted if a small fraction of the steady state electron energy is ejected into the nonthermal electrons. The size of radio emission region of our model is around several thousand gravitational radii, which is also roughly consistent with the recent high-resolution VLBI observations for some nearby LLAGNs.Comment: 10 pages, 5 figures, accepted for publication in Ap

Constraint on the black-hole spin of M87 from the accretion-jet model

The millimeter bump, as found in high-resolution multi-waveband observations of M87, most possibly comes from the synchrotron emission of thermal electrons in advection dominated accretion flow(ADAF). It is possible to constrain the accretion rate near the horizon if both the nuclear millimeter emission and its polarization are produced by the hot plasma in the accretion flow. The jet power of M87 has been extensively explored, which is around $8_{\rm -3}^{+7}\times10^{42} {\rm erg/s}$ based on the analysis of the X-ray cavity. The black hole(BH) spin can be estimated if the jet power and the accretion rate near the horizon are known. We model the multi-wavelength spectral energy distribution (SED) of M87 with a coupled ADAF-jet model surrounding a Kerr BH, where the full set of relativistic hydrodynamical equations of the ADAF are solved. The hybrid jet formation model, as a variant of Blandford-Znajek model, is used to model the jet power. We find that the SMBH should be fast rotating with a dimensionless spin parameter $a_{*}\simeq0.98_{\rm -0.02}^{+0.012}$.Comment: 6 pages, 1 figures,1 table, accepted for publication in MNRA

Revisit the fundamental plane of black-hole activity from sub-Eddington to quiescent state

It is very controversial whether radio--X-ray correlation as defined in LH state of XRBs can extend to quiescent state (e.g., X-ray luminosity less than a critical value of $L_{\rm X,c} \sim10^{-5.5}L_{\rm Edd}$) or not. In this work, we collect a sample of XRBs and low luminosity active galactic nuclei (LLAGNs) with wide distribution of Eddington ratios to reexplore the fundamental plane between 5 GHz radio luminosity, $L_{\rm R}$, 2-10 keV X-ray luminosity, $L_{\rm X}$, and black hole (BH) mass, $M_{\rm BH}$, namely $\log L_{\rm R}=\xi_{\rm X} \log L_{\rm X}+\xi_{\rm M}\log M_{\rm BH}+\rm constant$. For the whole sample, we confirm the former fundamental plane of Merloni et al. and Falcke et al. that $\xi_{\rm X}\sim 0.6$ and $\xi_{\rm M}\sim 0.8$ even after including more quiescent BHs. The quiescent BHs follow the fundamental plane very well, and, however, FR I radio galaxies follow a steeper track comparing other BH sources. After excluding FR Is, we investigate the fundamental plane for BHs in quiescent state with $L_{\rm X}< L_{\rm X,c}$ and sub-Eddington BHs with $L_{\rm X}> L_{\rm X,c}$ respectively, and both subsamples have a similar slope, $\xi_{\rm X}\sim0.6$, which support that quiescent BHs may behave similar to those in low-hard state. We further select two subsamples of AGNs with BH mass in a narrow range (FR Is with $M_{\rm BH}=10^{8.8\pm0.4}$ and other LLAGNs with $M_{\rm BH}=10^{8.0\pm0.4}$) to simulate the behavior of a single supermassive BH evolving from sub-Eddington to quiescent state. We find that the highly sub-Eddington sources with $L_{\rm X}/L_{\rm Edd}\sim10^{-6}-10^{-9}$ still roughly stay on the extension of radio--X-ray correlation as defined by other sub-Eddington BHs. Our results are consistent with several recent observations in XRBs that the radio--X-ray correlation as defined in low-hard state can extend to highly sub-Eddington quiescent state.Comment: 8 pages, 3 figures, MNRAS 453,3447-3454, 201

The Radio/Gamma Connection of Blazars from High to Low Radio Frequencies

We construct a large sample of gamma-ray blazars with low-frequency radio data using the recent released TGSS AD1 catalog at 150 MHz. The radio/gamma connections of blazars are compared from 143 GHz to 150 MHz. The radio flux density at all radio frequencies shows strong correlation with gamma-ray flux for blazars, as well as for the two subclasses, FSRQs and BL Lacs. But the correlations get worse from high to low radio frequencies, which indicates that the low-frequency radio emission is the mixture of extended and core components for blazars. In addition, we find that the correlation between 150 MHz radio flux density and gamma-ray flux is more significant for BL Lacs than that for FSRQs. The slope for the luminosity correlation between radio and gamma-ray also get flatter than unity at 150 MHz. These results indicate that the core dominance at 150 MHz for BL Lacs is larger than that for FSRQs. We also compare the radio luminosity from direct TGSS observation and the extended radiation at 150 MHz for blazars. The results show that the ratio between core and extended component at 150 MHz is about 1:1 on average.Comment: 10 pages, 6 figures, 2 tables, accepted by Ap

Jet Power of Jetted Active Galactic Nuclei: Implication for Evolution and Unification

We construct samples of jetted active galactic nuclei (AGNs) with low-frequency radio data from the recent released TGSS AD1 catalog at 150 MHz. With these samples, we compare the properties of jet power for blazars, radio-loud narrow-line Seyfert 1 galaxies (RL-NLS1s), young radio sources (YRSs) and radio galaxies. The jet-disk connection, and the unification of jetted AGNs are explored. On the Eddington ratio --- Eddington-scaled jet power plane, jetted AGNs can be generally divided into two populations. Low power radio galaxies, low excitation FR IIs (LEG/FR IIs), and most YRSs show larger jet power than accretion power, while FSRQs, RL-NLS1s, and high excitation FR IIs (HEG/FR IIs) are on the contrary. LEG/FR IIs share similar jet power properties with HEG/FR IIs, while their accretion properties are different with the latter. These facts suggest an evolutional sequence from HEG/FR IIs, LEG/FR IIs to FR Is, where the accretion and jet activities get dimmed gradually. LEG/FR IIs are the transitional objects that accretion processes have switched off, while jets are still active. After correcting the contribution from radio core of blazars, the unification between blazars and radio galaxies is confirmed with the jet power distributions. The unification involved RL-NLS1s is more complicated than the simple scenarios of black hole growth or orientation effect. In addition, our results manifest that low synchrotron peaked BL Lacs (LBLs) contain two distinct groups on the distribution of jet power, with one group similar with FSRQs and the other similar with intermediate synchrotron peaked BL Lacs. The LBLs with higher jet powers might be the aligned counterparts of LEG/FR IIs.Comment: 16 pages, 11 figures, 1 table, accepted by Ap

Constraints on minimum electron Lorentz factor and matter content of jets for a sample of bright Fermi blazars

We fit the (quasi-)simultaneous multi-waveband spectral energy distributions (SEDs) for a sample of low-synchrotron-peaked (LSP) blazars with a one-zone leptonic model. The seed photons that predominantly come from broad line region (BLR) and infrared (IR) molecular torus are considered respectively in external Compton process. We find that the modeling with IR seed photons is systematically better than that with BLR photons based on a $\chi^2$ test, which suggest that $\gamma$-ray emitting region most possibly stay outside the BLR. The minimum electron Lorentz factor, $\gamma_{\rm min}$, is constrained from the modeling for these LSP blazars with good soft X-ray data (ranges from 5 to 160 with a median value of 55), which plays a key role in jet power estimation. Assuming one-to-one ratio of proton and electron, we find that the jet power for LSP blazars is systematically higher than that of FR II radio galaxies at given 151 MHz radio luminosity, $L_{\rm 151MHz}$, even though FR IIs are regarded as same as LSP blazars in unification scheme except the jet viewing angle. The possible reason is that there are some $e^{\pm}$ pairs in the jet of these blazars. If this is the case, we find the number density of $e^{\pm}$ pairs should be several times higher than that of $e^{-}-p$ pairs by assuming the jet power is the same for LSP blazars and FR IIs at given $L_{\rm 151MHz}$.Comment: Accepted for publication in ApJS. 16 pages, 14 figures, 2 table

Accretion/Jet Activity and Narrow [O III] Kinematics in Young Radio Galaxies

We estimate black hole masses and Eddington ratios for a sample of 81 young radio galaxies (42 CSS +39 GPS). We find that the average black hole (BH) mass of these young radio galaxies is ~8.3, which is less than that of radio loud QSOs and low redshift radio galaxies. The CSS/GPS sources have relatively high Eddington ratios, with an average value of <log Lbol/LEdd>=-0.75, which are similar to those of narrow line Seyfert 1 galaxies (NLS1s). This suggests that young radio galaxies may not only be in the early stages of their radio activity, but also in the early stage of their accretion activity. We find that the young radio galaxies as a class deviate systematically from M_bh-\sigma relation defined by nearby inactive galaxies, when using [O III] as a surrogate for stellar velocity dispersion, \sigma_* . We also find that the deviation of the [O III] line width is correlated with the Eddington ratio and sources with Lbol/LEdd~1 have the largest deviations, which are similar to those of radio quiet QSOs/NLS1s (radio jets is absent or weak). A similar result has been obtained for 9 linear radio Seyfert galaxies. On the basis of these results, we suggest that, in addition to the possible jet-gas interactions, accretion activities may also play an important role in shaping the kinematics of the narrow [O III] line in young radio galaxies and linear radio Seyferts.Comment: 5 pages, 4 figures, accepted by Science in China Series-G (BH issue), only PDF, which is relate to recent two papers arXiv:0905.3663(MNRAS, in press) and arXiv:0907.2234 (ApJL, in press

Modelling the `outliers' track of the radio--X-ray correlation in X-ray binaries based on disc-corona model

The universal radio--X-ray correlation (F_R \propto F_X^{b}, b~0.5-0.7) has been found for a sample of black-hole X-ray binaries (BHBs) in their low/hard states, which can roughly be explained by the coupled model of jet and radiatively inefficient advection dominated accretion flow. However, more and more `outliers' were found in last few years, which evidently deviate from the universal radio-X-ray correlation and usually show a much steeper correlation with an index of ~1.4. Based on simple physical assumptions, the radiatively efficient accretion flows are speculated to exist in these `outliers'. In this work, we test this issue by modelling the `outliers' track based on the radiatively efficient disc-corona model and the hybrid jet model. We find that our model predicts a steeper radio--X-ray correlation with slopes >~1.2 for the typical viscosity parameter of \alpha~0.05-0.2. In particular, the slope is ~1.4 for the case of \alpha~0.1, which is consistent with the observational results of H1743-322 very well. Our results suggest that the `outliers' track may be regulated by the disc-corona model.Comment: 7 pages, 3 figures, accepted for publication in MNRA

Different X-ray spectral evolution for black hole X-ray binaries in dual tracks of radio-X-ray correlation

Recently an `outliers' track of radio-X-ray correlation was found, which is much steeper than the former universal correlation, where dual tracks were speculated to be triggered by different accretion processes. In this work, we test this issue by exploring hard X-ray spectral evolution in four black-hole X-ray binaries (XRBs) with multiple, quasi-simultaneous radio and X-ray observations. Firstly, we find that hard X-ray photon indices, $\Gamma$, are anti- and positively correlated to X-ray fluxes when the X-ray flux, $F_{\rm 3-9keV}$, is below and above a critical flux, $F_{\rm X,crit}$, which are consistent with prediction of advection dominated accretion flow (ADAF) and disk-corona model respectively. Secondly and most importantly, we find that the radio-X-ray correlations are also clearly different when the X-ray fluxes are higher and lower than the critical flux that defined by X-ray spectral evolution. The data points with $F_{\rm 3-9keV}\gtrsim F_{\rm X,crit}$ have a steeper radio-X-ray correlation ($F_{\rm X}\propto F_{\rm R}^{b}$ and $b\sim 1.1-1.4$), which roughly form the `outliers' track. However, the data points with anti-correlation of $\Gamma-F_{\rm 3-9keV}$ either stay in the universal track with $b\sim0.61$ or stay in transition track (from the universal to `outliers' tracks or vice versa). Therefore, our results support that the universal and `outliers' tracks of radio-X-ray correlations are regulated by radiatively inefficient and radiatively efficient accretion model respectively.Comment: Accepted for publication in ApJ; 10 pages, 5 figures, 5 table