Qingwen Wu

The X-Ray Spectral Evolution in X-Ray Binaries and Its Application to Constrain the Black Hole Mass of Ultraluminous X-Ray Sources

We investigate 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 X-ray binaries (XRBs) with well-constrained black hole masses and distances. We find that different XRBs follow different anticorrelations between Gamma and xi when xi is less than a critical value, while Gamma and xi generally follow the same positive correlation when xi is larger than the critical value. The anticorrelation and the positive correlation may suggest that they are in different accretion modes ( e. g., radiatively inefficient accretion flow [RIAF] and standard disk). We fit both correlations with the linear least-squares method for individual sources, from which the cross point of two fitted lines is obtained. Although the anticorrelation varies from source to source, the cross points of all sources roughly converge to the same point with small scatter (log xi = -2.1 +/- 0.2, Gamma = 1.5 +/- 0.1), which may correspond to the transition point between RIAF and standard accretion disk. Motivated by the observational evidence for the similarity of the X-ray spectral evolution of ultraluminous X-ray sources (ULXs) to that of XRBs, we then constrain the black hole masses for seven ULXs, assuming that their X-ray spectral evolution is similar to that of XRBs and that their Eddington ratios are less than 1. We find that the BH masses of these seven luminous ULXs are around 104 M(circle dot), which are typical for intermediate-mass BHs ( IMBHs). Our results are generally consistent with the BH masses constrained from the timing properties ( e. g., break frequency) or the model fitting with a multicolor disk.

LORENTZ-FACTOR–ISOTROPIC-LUMINOSITY/ENERGY CORRELATIONS OF GAMMA-RAY BURSTS AND THEIR INTERPRETATION

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (Γ0) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between Γ0 and isotropic γ -ray energy: Γ0 ∝ E 0.25 γ, iso,52 . By including more GRBs with updated data and more methods to derive Γ0, we confirm this correlation and obtain Γ0 � 91E 0.29 γ, iso,52 . Evaluating the mean isotropic γ -ray luminosities L γ, iso of the GRBs in the same sample, we discover an even tighter correlation Γ0 � 249L 0.30 γ, iso,52 . We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive Γ0 ∝ L 0.22 γ, iso , which is consistent with the data. This suggests that the central engine of long GRBs

On the origin of X-ray emission in some FR I galaxies: ADAF or jet?

We investigate the origin of X-ray emission in FR I galaxies using radio, submillimeter, optical, and Chandra X-ray data for a small sample of eight FR I sources. These sources are very dim, with X-ray luminosities L(X)/L(Edd) similar to 10(-4) to 10(-8) (with L(X) the X-ray luminosity between 2 and 10 keV). We try to fit the multi-wave-band spectra using a coupled accretion-jet model. In this model, the accretion is described by an advection-dominated accretion flow (ADAF); in the innermost region of the ADAF, a fraction of the flow is transferred into the vertical direction and forms a jet. We find that X-ray emission in the source with the highest L(X) (similar to 1.8 x 10(-4) L(Edd)) is from the ADAF. The results for the four sources with moderate L(X) (several times 10(-6) L(Edd)) are complicated. Two are dominated by the ADAF, one by the jet, and the other by the sum of the jet and ADAF. The X-ray emission in the three least luminous sources ( L(X) less than or similar to 1.0 x 10(-6) L(Edd)) is mainly from the jet, although for one source it can also be interpreted as the ADAF, since the quality of the X-ray data is low. We conclude that these results roughly support the prediction of Yuan & Cui that when the X-ray luminosity of a system is below some critical value, the X-radiation will not be dominated by the emission from the ADAF any longer, but by the jet. We also investigate the fuel supply in these sources. We find that the accretion rate in four of the five sources for which we have good constraints must be higher than the Bondi rate. This implies that another fuel supply, such as gas released by the stellar population inside the Bondi radius, should be important.

The black hole mass, Eddington ratio and MBH–σ[O iii] relation in young radio galaxies

The masses of the central supermassive black holes (BHs) and the Eddington ratios for a sample of 65 young radio galaxies [27 gigahertz-peaked spectrum (GPS) and 38 compact steep-spectrum (CSS) sources] are estimated by various methods. We find that the average BH mass of these young radio galaxies is (log M BH ) ≃ 8.3, which is less than that of radio loud quasi-stellar objects (QSOs) and low-redshift radio galaxies ((log M BH > ≃ 9.0). The CSS/GPS sources have relatively high Eddington ratios with average ratio (log L bol /L Edd > = ―0.56, which are similar to those of narrow-line Seyfert 1 galaxies (NLSls). It suggests that the CSS/GPS sources may not only be in the early stage of radio activities, but also in the early stage of their accretion activities. We find that the young radio galaxies as a class deviate systematically from the M BH ―σ * relation defined by nearby inactive galaxies, when using σ [O III as a surrogate for the stellar velocity dispersion σ * . There is no significant correlation between the deviation of the [O m] emission line width, Δσ ≡ σ [OIII] ― σ [pred] and the jet/accretion power, where σ [pred] are calculated from the Tremaine et al. relation using the estimated BH masses. However, we find that the deviation Δσ in young radio galaxies is well correlated with the Eddington ratio, and this correlation is found to be similar to that of radio quiet active galactic nuclei (AGN) (QSOs/NLSls) where the radio jet is absent or weak. We suggest that the accretion activities may still play an important role in shaping the kinematics of [O III] narrow line in these young radio galaxies.

A PHYSICAL LINK BETWEEN JET FORMATION AND HOT PLASMA IN ACTIVE GALACTIC NUCLEI

Recent observations suggest that in black hole X-ray binaries jet/outflow formation is related to the hot plasma in the vicinity of the black hole, either in the form of an advection-dominated accretion flow at low accretion rates or in a disk corona at high accretion rates. We test the viability of this scenario for supermassive black holes using two samples of active galactic nuclei distinguished by the presence (radio-strong) and absence (radio-weak) of well-collimated, relativistic jets. Each is centered on a narrow range of black hole mass but spans a very broad range of Eddington ratios, effectively simulating in a statistical manner the behavior of a single black hole evolving across a wide spread in accretion states. Unlike the relationship between the radio and optical luminosity, which shows an abrupt break between high- and low-luminosity sources at an Eddington ratio of ~1%, the radio emission?a measure of the jet power?varies continuously with the hard X-ray (2-10?keV) luminosity, roughly as . This relation, which holds for both radio-weak and radio-strong active galaxies, is similar to the one seen in X-ray binaries. Jet/outflow formation appears to be closely linked to the conditions that give rise to the hot, optically thin coronal emission associated with accretion flows, both in the regime of low and high accretion rates.

OBSERVATIONAL EVIDENCE FOR YOUNG RADIO GALAXIES IS TRIGGERED BY ACCRETION DISK INSTABILITY

The bolometric luminosities and black hole (BH) masses are estimated by various methods for a sample of young radio galaxies with known ages. We find that the ages are positively correlated with the bolometric luminosities in these young radio galaxies, which is consistent with theoretical prediction based on radiation pressure instability of accretion disk in Czerny et al. The ages of young radio galaxies are also found to be consistent with the theoretical durations of outbursts in BH mass and accretion rate (in Eddington unit) plane, where the outbursts are assumed to be triggered by the radiation pressure instabilities. Our results provide the observational evidence for the radiation pressure instability, which causes limit-cycle behavior, as a physical mechanism that may be responsible for these short-lived young radio galaxies.

ON THE BL LACERTAE OBJECTS/RADIO QUASARS AND THE FR I/II DICHOTOMY

In the frame of unification schemes for radio-loud active galactic nuclei (AGNs), FR I radio galaxies are believed to be BL Lacertae (BL Lac) objects with the relativistic jet misaligned to our line of sight, and FR II radio galaxies correspond to misaligned radio quasars. The Ledlow-Owen dividing line for the FR I/FR II dichotomy in the optical absolute magnitude of the host galaxy-radio luminosity (M(R)-L(Rad)) plane can be translated to the line in the black hole mass-jet power (M(bh)-Q(jet)) plane by using two empirical relations: Q(jet)-L(Rad) and M(bh)-M(R). We use a sample of radio quasars and BL Lac objects with measured black hole masses to explore the relation of the jet power with black hole mass, in which the jet power is estimated from the extended radio emission. It is found that the BL Lac objects are clearly separated from radio quasars by the Ledlow-Owen FR I/II dividing line in the M(bh)-Q(jet) plane. This strongly supports the unification schemes for FR I/BL Lac object and FR II/radio quasar. We find that the Eddington ratios L(bol)/L(Edd) of BL Lac objects are systematically lower than those of radio quasars in the sample with a rough division at L(bol)/L(Edd) similar to 0.01, and the distribution of Eddington ratios of BL Lac objects/quasars exhibits a bimodal nature, which imply that the accretion mode of BL Lac objects may be different from that of radio quasars.

Constraints on the 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

ORIGIN OF RADIO EMISSION FROM NEARBY LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

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POSSIBLE ORIGIN OF RADIO EMISSION FROM NONTHERMAL ELECTRONS IN HOT ACCRETION FLOWS FOR LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

test, which suggest that