arXiv subjects

Jian-Min Wang

Publications and source records attributed to Jian-Min Wang.

At least 199 records · Page 11Linked to original sources

arXiv2005

The Afterglows of Ultraluminous Quasars

Quasars represent a brief phase in the life-cycle of most massive galaxies, but the evolutionary connection between central black holes and their host galaxies remains unclear. While quasars are active and shining brighter than the Compton-limit luminosity, their radiation heats the surrounding medium to the Compton temperature, forming Compton spheres extending to the Strömgren radius of Fe$^{26+}$/He$^{2+}$. After the quasars shut off, their ``afterglow'' can be detected through three signatures: (1) an extended X-ray envelope, with a characteristic temperature of $\sim 3\times 10^7$ K; (2) Ly$α$ and Ly$β$ lines and the $K-$edge of Fe$^{26+}$; and (3) nebulosity from hydrogen and helium recombination emission lines. We discuss the possibility of detecting these signatures using {\em Chandra}, the planned {\em XEUS} mission, and ground-based optical telescopes. The luminosity and size of quasar afterglows can be used to constrain the lifetime of quasars.

astro-ph↗

arXiv2004

Collisions among Clouds inside Dusty Torus in Active Galactic Nuclei: Observational Consequences

A geometrically thick dusty torus in NGC 1068 has been unambiguously resolved by an infrared interferometry telescope. This implies clouds composing the dusty torus are undergoing supersonic collisions with each other. We show that the collisions form strong non-relativistic shocks, which accelerate populations of relativistic electrons. Torus reprocesses emission from accretion disk into infrared band. We show that the energy density of the infrared photons inside the torus is much higher than that of the magnetic field in the clouds and the seed photons of inverse Compton scattering are mainly from the infrared ones. The maximum energy of the relativistic electrons can reach a Lorentz factor of $10^5$. We calculate the spectrum of the synchrotron and inverse Compton scattering radiation from the electrons in the torus. The relativistic electrons in the torus radiate non-thermal emission from radio to $γ$-ray, which isotropically diffuses in the region of the torus. We find the most prominent character is a peak at $\sim 0.5-1$ GeV. We apply this model to NGC 1068 and find that the observed radio emission from the core component $S_1$ can be explained by the synchrotron emission from the relativistic electrons. We predict that there is a $γ$-ray emission with a luminosity of $10^{40}$ erg/s peaking at $\sim 1$ GeV from the torus, which could be detected by {\em Gamma-Ray Large-Array Space Telescope} in the future. This will provide a new clue to understand the physics in the torus. The non-thermal radiation from dusty torus may explain the radio emission from Seyfert galaxies. The cosmological implications of the non-thermal emission to the $γ$-ray background radiation have been discussed.

astro-ph↗

arXiv2004

The Connection Between Jets, Accretion Disks, and Black Hole Mass in Blazars

The properties of relativistic radio jets are thought to be closely connected with the properties of accretion disks in active galactic nuclei. We explore this issue using a sample of 35 blazars with very-long baseline observations, for which we can estimate the kinetic powers of their relativistic jets, the bolometric luminosity of their accretion disks, and the masses of their black holes. Contrary to previous claims, we find that the jet kinetic power is significantly correlated with the disk luminosity. This supports the notion that the disk is somehow coupled to the jet, even on parsec scales. Moreover, we show that the correlation improves by including the black hole mass as a second parameter. The dominance of the jet, parameterized as the ratio of the jet kinetic power to the disk luminosity, is largely controlled by and is inversely correlated with the Eddington ratio of the accretion disk. This empirical relation should serve as a useful guide for theoretical models for jet formation.

astro-ph↗

arXiv2004

Narrow Iron K$α$ Lines in Active Galactic Nuclei: Evolving Populations?

We assemble a sample consisting of 66 active galactic nuclei (AGNs) from literature and the {\em XMM-Newton} archive in order to investigate the origin of the 6.4 keV narrow iron K$α$ line (NIKAL). The X-ray Baldwin effect of the NIKAL is confirmed in this sample. We find the equivalent width ($EW$) of the NIKAL is more strongly inversely correlated with Eddington ratio ($\ce$) than the 2-10 keV X-ray luminosity. Our sample favors the origin from the dusty torus and the X-ray Baldwin effect is caused by the changing opening angle of the dusty torus. The relation $EW-\ce$ can be derived from a toy model of the dusty torus. If the unification scheme is valid in all AGNs, we can derive the Baldwin effect from the fraction of type {\sc ii} AGNs to the total population given by {\em Chandra} and {\em Hubble} deep surveys. Thus the evolution of populations could be reflected by the NIKAL's Baldwin effect.

astro-ph↗

arXiv2004

Hot Disk Corona and Magnetic Turbulence in Radio-Quiet Active Galactic Nuclei: Observational Constraints

We compile a sample consisting of 56 radio-quiet active galactic nuclei so as to investigate statistical properties of hot corona of accretion disks from {\em ASCA} observations. The black-hole masses in the sample are estimated via several popular methods and the bolometric luminosities from the multi-wavelength continuum. This allows us to estimate the Eddington ratio (${\cal E}\equiv L_{\rm Bol}/L_{\rm Edd}$) so that the undergoing physical processes can be tested via hard X-ray data. We find a strong correlation between ${\cal F}_{\rm X}\equiv L_{\rm 2-10keV}/L_{\rm Bol}$ and ${\cal E}$ as ${\cal F}_{\rm X}\propto {\cal E}^{-0.64}$ with a multivariate regression. This indicates that the release of gravitational energy in the hot corona is controlled by the Eddington ratio. On the other hand, the correlation between the hard X-ray spectral index ($Γ$) and ${\cal E}$ depends critically on the types of objects: $Γ$ is nearly constant ($Γ\propto {\cal E}^0$) in broad-line Seyfert 1's (BLS1s), whereas $Γ\propto \log {\cal E}^{0.18}$ in narrow-line Seyfert 1's (NLS1s), although not very significant. We can set constraints on the forms of magnetic stress tensor on the condition that ${\cal F}_{\rm X}$ is proportional to the fraction $f$ of gravitational energy dissipated in the hot corona and that $f$ is proportional to magnetic energy density in the disk. We find that the shear stress tensor $t_{rϕ}\propto P_{\rm gas}$ is favored by the correlation in the present sample, where $P_{\rm gas}$ is the gas pressure.

astro-ph↗

arXiv2004

A possible feature of thermal matter in relativistic jets of radio-loud quasars

It has been suggested that relativistic jets in quasars may contain a considerable amount of thermal matter. In this paper, we explore the possibility that the K-alpha line from the thermal matter may appear at tens of keV due to a high Doppler blue-shift. In the jet comoving frame, the energy density of photons originally emitted by the accretion disk and reflected off the broad line region clouds dominates over that of photons of other origin. We discuss the photoionization states of the thermal matter and find that the irons elements are neutral. The high metallicity in quasars enhances the possibility to detect the thermal matter in the relativistic jet in some radio-loud quasars. A highly Doppler blue-shifted K-alpha line may be detected. We make a rediction for 3C 273, in which the K-alpha line luminosity might be of the order $3.0\times 10^{44}$ erg/s with an equivalent width of 2.4 keV. Such a line could be detected in a future mission.

astro-ph↗

arXiv2004

The Additional Line Component within the Iron KαProfile in MCG-6-30-15: Evidence for Blob Ejection?

The EPIC data of MCG -6-30-15 observed by XMM-Newton were analyzed for the complexities of the iron K-alpha line. Here we report that the additional line component (ALC) at 6.9 keV undoubtedly appears within the broad iron Kalpha; line profile at the high state, whereas it disappears at the low state. These state-dependent behaviors exclude several possible origins and suggest an origin of the ALC in matter being ejected from the vicinity of the black hole. At the low state, the newborn blob ejected from the accretion disk is so Thomson-thick that hard X-rays are blocked from ionizing the old blobs, leading to the disappearance of the ALC. When the blob becomes Thomson-thin as a result of expansion, the hard X-ray will penetrate it and ionize the old ones, emitting the ALC at the high state. The blob ejection is the key to switching the ALC on or off.

astro-ph↗

arXiv2004

Slim Disks with Transition Regions and Applications to Microquasars and Narrow Line Seyfert 1 Galaxies

Slim disks have been received much attention because of the increasing evidence for the super-critical accreting objects. In this paper, we make an attempt to construct a unified model, in which the viscosity and the dimensionless accretion rate can span rather wide ranges. We replace blackbody radiation under diffusion approximation with a bridged formula, which accounts for both blackbody radiation and thermal bremsstrahlung in optically-thick and -thin cases, respectively. Thus this allows us to investigate the structures of and the emergent spectra from slim disks in a wider parameter space, covering transition regions from optically thick to optically thin. We show that there is a maximum transition radius, roughly $R_{\rm tr, max}/R_g\sim 50$ when $\dot{M}/\dot{M}_{\rm C}\sim 15$. The emergent spectra from the unified model of the accretion disk have been calculated. A simple model of hot corona above the slim disk is taken into account for the hard X-ray spectrum in this paper based on Wang & Netzer (2003). We have applied the present model to the microquasar GRS 1915+105, narrow line Seyfert 1 galaxies RE J1034+396 and Akn 564. Our model can explain well the broadband X-ray spectra of narrow line Seyfert 1 galaxies, microquasars and possible ultra-luminous compact X-ray sources. The present model can be widely applied to the candidates of super-critical accreting objects.

astro-ph↗

arXiv2003

The Central Engines of Radio-Loud Quasars

We have assembled a sample of 37 RLQs that have been imaged with the HST in order to investigate their black hole masses, accretion rates, and the structure of their accretion disks. The black hole masses were estimated from the luminosities of the host galaxies, and the accretion powers were extrapolated from the emission-line luminosities. The majority of the quasars have masses in the range $M_{\rm BH} \approx 10^8-10^9$ solar mass. Their accretion rates, $\dot M \approx 0.01-1$ times the Eddington rate, suggest that most of the objects possess standard optically thick, geometrically thin accretion disks, in some cases perhaps accompanied by an optically thin advection-dominated component. The coexistence of strong radio emission and a standard disk conflicts with recent models for jet formation. We discuss modifications of the standard model that can resolve this discrepancy. We find there is a strong correlation between the accretion rate and the extended radio luminosity. This lends support to the idea that the extended radio emission is somehow linked to the accretion disk. Lastly, we combine the present sample of radio-loud quasars with the sample of BL Lac objects to reevaluate the unification picture for radio-loud AGNs. Consistent with current ideas for the unification of radio-loud sources, we find that flat-spectrum radio quasars and FR II radio galaxies indeed seem to belong to the same population, as do BL Lacs and FR I radio galaxies on the opposite end of the luminosity spectrum. However, some members of the low frequency-peaked BL Lac objects may be more closely associated with FR II rather than FR I radio galaxies. We describe how the various subclasses of radio-loud sources can be viewed as a continuous sequence of varying accretion rate.

astro-ph↗

arXiv2003

A Limit Relation between Black Hole Mass and H$β$ Width: Testing Super-Eddington Accretion in Active Galactic Nuclei

(abbreviated) We show that there is a limit relation between the black hole mass and the width at the half maximum of H$β$ for active galactic nuclei (AGNs) with super-Eddington accretion rates. When a black hole has a super-Eddington accretion rate, the empirical relation of reverberation mapping has two possible ways. First, it reduces to a relation between the black hole mass and the size of the broad line region due to the photon trapping effects inside the accretion disk. For the Kaspi et al.'s empirical reverberation relation, we get the limit relation as $M_{\rm BH}=(2.9 - 12.6)\times 10^6M_{\odot} (\upsilon_{\rm FWHM}/10^3{\rm km s^{-1}})^{6.67}$, called as the Eddington limit. Second, the Eddington limit luminosity will be relaxed if the trapped photons can escape from the magnetized super-Eddington accretion disk via the photon bubble instability, and the size of the broad line region will be enlarged according to the empirical reverberation relation, leading to a relatively narrow width of H$β$. We call this the Begelman limit. Super-Eddington accretions in a sample composed of 164 AGNs have been searched by this limit relation. We find there are a handful of objects locate between the Eddington and Begelman limit lines, they may be candidates of super-Eddington accretors in a hybrid structure of photon trapping and photon bubble instability. The maximum width of H$β$ is in the reange of $(3.0 - 3.8)\times 10^3$ km s$^{-1}$ for the maximum mass black holes with super-Eddington accretion rates among AGNs. We suggest that this limit relation is more reliable and convenient to test whether a source is super-Eddington and useful to probe the structure of the super-Eddington accretion process.

astro-ph↗

arXiv2002

Extreme Slim Accretion Disks and Narrow Line Seyfert 1 Galaxies: the Nature of the soft X-ray Hump

We present a detailed model of an extreme slim disk (ESD) with a hot corona around a massive black hole with dimensionless accretion rate $\dotm$ in the range $2.5\ll \dotm\leq 100$. We assume that a fraction $f$ of the gravitational energy is released in the hot corona and the rest is released in the ESD. The energy equation of the ESD is dominated by advection and the spectrum shows a broad ``hump'' caused by saturated Comptonization with monochromatic luminosity given by $νL_ν\propto ν^0$. This relationship enables us to estimate the black hole mass from the ESD luminosity. The spectrum of the hot corona is sensitive to the parameter $f\dotM$ and the viscosity and shows a Comptonized power-law with a high-energy cutoff. The model is used to explain the spectral properties of narrow line Seyfert 1 galaxies (NLS1s). In particular, it can explain the spectrum of extreme NLS1s like NLS1 RE J1034+396. Our spectral estimate of the black hole mass in this source is in good agreement with the mass obtained by applying the reververation mapping correlation. We also examine the Eddington ratios in a large NLS1 sample and find that most objects show super-Eddington accretion rates. We argue that soft X-ray humps in NLS1s are natural consequences of super-Eddington accretion in such objects.

astro-ph↗

arXiv2002

The Accretion Rates and Spectral Energy Distributions of BL Lacertae Objects

We investigate the relationship between accretion rates and the spectral energy distributions (SEDs) of BL Lac objects, using a sample of objects for which published information on the host galaxies, emission-line luminosities, and peak frequencies and luminosities of their SEDs are available. The sample is composed of 43 BL Lac objects which have a relatively continuous distribution of peak frequencies. Under the assumption that the observed emission lines are photoionized by the central accretion disk, we use the line luminosities to estimate the accretion luminosities and hence accretion rates. We find that low frequency-peaked BL Lac objects (LBLs) span a wide range of accretion rates, whereas high frequency-peaked BL Lac objects (HBLs) cover a more restricted range of lower values. There appears to be a continuous distribution of accretion rates between the two subclasses of BL Lac objects. We find that the peak frequency of the SED, $\pknu$, correlates with the accretion rate, approximately with the form $\pknu\propto Λ^{-3}$ in HBLs and $\pknu \propto Λ^{-0.25}$ in LBLs, where $Λ\equiv L_{\rm lines}/c^2$. The peak luminosity of the SED is also correlated with $Λ$. These results suggest that the accretion rate influences the shape of the SED in BL Lac objects. They also support models which couple the jet and the accretion disk. We present a physical scenario to account for the empirical trends.

astro-ph↗

arXiv2001

The Mass Distribution of Black Holes in BL Lacertae Objects

In this {\it Letter}, we make an attempt to estimate the masses of black holes and their distributions in BL Lac objects. We find there is a bimodal population of black hole masses in BL Lacs: the first has a lower-mass peak centred at $\sim 7.0 \times 10^6\sunm$ composed of high frequency-peaked BL Lacs (HBLs) and the second is a higher-mass ($>10^9\sunm$) population composed of low frequency-peaked BL Lacs (LBLs). The low mass family of black holes in HBLs does not satisfy the Magorrian et al. relation whereas the high mass family in LBLs does this relation and is in agreement with Laor's limit. The origination of the bimodal distribution of black hole mass remains open.

astro-ph↗

arXiv2001

Blob Ejection from Advection-dominated Accretion Flow II: the Multiwavelength Properties of Light Curves

It has been argued that blobs ejected from advection-dominated accretion flow through the accretion-ejection instability undergo expansion due to their high internal energy density. The expanding blobs interact with their surroundings and form strong shock, which accelerates a group of electrons to be relativistic. Then flares are formed. This model has advances in two aspects: shock acceleration and self-consistent injection. We derive an analytical formula of the injection function of relativistic electrons based on the Sedov's law. We calculate the time-dependent spectrum of relativistic electrons in such an expanding blob. The light-travel effect, the evolution of the electron spectrum due to energy loss, and the escape of relativistic electrons from the radiating region are considered, as well as the expansion (at sub-relativistic speed) of the coasting blob. A large number of light curves spanning wide spaces of parameters have been given in this paper. Regarding the symmetry, relative amplitude, duration of a flare, and the time lag between peak fluxes, we find four basic kinds of light curves for the non-expanding blob, and seven basic kinds of light curves for the expanding blob. We also calculate the evolution of the photon spectrum from both non-expanding and expanding blobs. Different shapes in the phase of decreasing luminosity are then obtained for different parameter values. The photon index, $α_{\rm ph}$, keeps constant for non-expanding blobs when luminosity decreases, whereas $α_{\rm ph}$ continues to decrease after the luminosity reaches its maximum for expanding blobs. It is expected that we can extract the information of ejected blobs from the observed light curves based on the present model.

astro-ph↗

arXiv2001

Growth of supermassive black holes and metallicity in quasars

The strong correlation between the mass of the central supermassive black hole (SMBH) and the bulge in some galaxies and quasars implies that the formation of the black hole is somehow linked to the bulge. The measurement of metallicity by NV/CIV or NV/HeII in quasars allows to discuss a possible way of formation of the black hole. In this Letter we trace the metallicity along the possible routes in Rees' diagram in order to test the ways by which SMBHs can form. We derive a relation between the metallicity and the mass of the SMBH as $Z\propto M_{BH}$ based on the numerical simulation of the evolution of star clusters. It is in good agreement with the relation determined by the metallicity measured by NV/CIV or NV/HeII in Hamann & Ferland's sample. This lends observational support to the formation of SMBHs via routes R4 or R5, namely, the evolution of dense star clusters.

astro-ph↗

arXiv2000

Blob ejection from advection-dominated accretion flow: observational consequences

There is increasing evidence for the presence of an optically thin advection-dominated accretion flow (ADAF) in low luminosity active galactic nuclei and radio-loud quasars. The present paper is devoted to explore the fate of a blob ejected from an ADAF, and to discuss its observational consequences. It is inevitable for the ejected blob to drastically expand into its surroundings. Consequently, it is expected that a group of relativistic electrons should be accelerated, which may lead to nonthermal flares, since a strong shock will be formed by the interaction between the blob and its surroundings. Then the blob cools down efficiently, leading to the appearance of recombination lines about $10^5$s after its ejection from an ADAF. We apply this model to NGC 4258 for some observational prediction, and to PKS 2149--306 for the explanation of observational evidence. Future simultaneous observations of recombination X-ray lines and continuum emission are highly desired to test the present model.

astro-ph↗

arXiv2000

The profile of an emission line from relativistic outflows around a black hole

Recent observations show strong evidence for the presence of Doppler-shifted emission lines in the spectrum of both black hole candidates and active galactic nuclei. These lines are likely to originate from relativistic outflows (or jets) in the vicinity of the central black hole. Consequently, the profile of such a line should be distorted by strong gravitational effects near the black hole, as well as special relativistic effects. In this paper, we present results from a detailed study on how each process affects the observed line profile. We found that the profile is sensitive to the intrinsic properties of the jets (Lorentz factor, velocity profile, and emissivity law), as well as to the spin of the black hole and the viewing angle (with respect to the axis of the jets). More specifically, in the case of approaching jets, an intrisically narrow line (blue-shifted) is seen as simply broadened at small viewing angles, but it shows a doubly peaked profile at large viewing angles for extreme Kerr black holes (due to the combination of gravitational focusing and Doppler effects); the profile is always singly peaked for Schwarzschild black holes. For receding jets, however, the line profile becomes quite complicated owing to complicated photon trajectories. To facilitate comparison with observations, we searched a large parameter space to derive representative line profiles. We show the results and discuss how to use emission lines as a potential tool for probing the inner region of a black hole jet system.

astro-ph↗

arXiv2000

Intrinsic constraints on very high energy emission in gamma-ray loud blazars

Photons with very high energy up to TeV (VHE) emitted from active galactic nuclei (AGNs) provide some invaluable information of the origin of $\gam$-ray emission. Although 66 blazars have been detected by {\it EGRET}, only three low redshift X-ray selected BL Lacs (Mrk 421, Mrk 501, and 1ES 2344+514) are conclusive TeV emitters (PKS 2155-304 is a potential TeV emitter) since VHE photons may be absorbed by cosmological background infrared photons ({\it external} absorption). Based on the ``mirror'' effect of clouds in broad line region, we argue that there is an {\it intrinsic} mechanism for the deficiency of TeV emission in blazars. Employing the observable quantities we derive the pair production optical depth $\tgg(\eps_{\rm obs})$ due to the interaction of VHE photons with the reflected synchrotron photons by electron Thomson scattering in broad line region. This sets a more strong constraints on very high energy emission, and provides a sensitive upper limit of Doppler factor of the relativistic bulk motion. It has been suggested to distinguish the {\it intrinsic} absorption from the {\it external} by the observation on variation of multiwavelegenth continuum.

astro-ph↗