Active galactic nuclei- the physics of individual sources and the cosmic history of formation and evolution

In this paper we give a brief review of the astrophysics of active galactic nuclei （AGNs）. After a general introduction motivating the study of AGNs, we discuss our present understanding of the inner workings of the central engines, most likely accreting black holes with masses between 106 and 10^10M. We highlight recent results concerning the jets （collimated outflows） of AGNs derived from X-ray observations （Chandra） of kpc-scale jets and ~/-ray observations of AGNs （Fermi, Cherenkov telescopes） with jets closely aligned with the lines of sight （blazars）, and discuss tile interpretation of these observations. Subsequently, we summarize our knowledge about the cosmic history of AGN formation and evolution. We conclude with a description of upcoming observational opportunities.

Tidally disrupted dusty clumps as the origin of broad emission lines in active galactic nuclei

With the support by the National Natural Science Foundation of China,a collaboration led by Prof.Wang Jianmin(王建民)from the Institute of High Energy Physics,Chinese Academy of Sciences proposes a new mechanism for the origin of the broad-line region in Active Galactic Nuclei,which was published

The THU-NAOC transient survey: the performance and results from the first year

The Tsinghua University-National Astronomical Observatories, Chinese Academy of Sciences （NAOC） Transient Survey is an automatic survey that conducts a systematic exploration of optical transients. This project utilizes a 60/90 cm Schmidt telescope at the Xinglong Station of NAOC. This survey repeatedly covers - 1000 square degrees of the northern sky with a cadence of 34 d. With an exposure of 60 s, the survey reaches a limiting unfiltered magnitude of about 19.5 mag, which enables us to discover supernovae in their relatively young stages. We describe the overall performance of our survey during the first year and present some preliminary results.

Detection of a high-confidence quasi-periodic oscillation in radio light curve of the high redshift FSRQ PKS J0805–0111

In this work,we have searched for quasi-periodic oscillations(QPOs)in the 15 GHz light curve of the FSRQ PKS J0805-0111 monitored by the Owens Valley Radio Observatory(OVRO)40 m telescope during the period from 2008 January 9 to 2019 May 9,using the weighted wavelet Z-transform(WWZ)and the Lomb-Scargle Periodogram(LSP)techniques.This is the first time to search for a periodic radio signal in the FSRQ PKS J0805-0111 by these two methods.Both methods consistently reveal a repeating signal with a periodicity of 3.38±0.8 yr(>99.7%confidence level).In order to determine the significance of the periods,the false alarm probability method was applied,and a large number of Monte Carlo simulations were performed.As possible explanations,we discuss a number of scenarios including the thermal instability of thin disks scenario,the spiral jet scenario and the binary supermassive black hole scenario.We expect that the binary black hole scenario,where the QPO is caused by the precession of binary black holes,is the most likely explanation.FSRQ PKS J0805-0111 thus could be a good binary black hole candidate.In the binary black hole scenario,the distance between the primary black hole and the secondary black hole is about 1.71×10^(16) cm.

SDSS J1042-0018:a Broad Line AGN but Misclassified as an HⅡGalaxy in the BPT Diagram by Flux Ratios of Narrow Emission Lines

In this paper,we discuss properties of SDSS J1042-0018 which is a broad line active galactic nucleus(AGN)but misclassified as an H II galaxy in the BPT diagram(SDSS J1042-0018 is called a misclassified broad line AGN).The emission lines around Hαand around Hβare well described by different model functions,considering broad Balmer lines to be described by Gaussian or Lorentz functions.Different model functions lead to different determined narrow emission line fiuxes,but the different narrow emission line fiux ratios lead SDSS J1042-0018 as an H II galaxy in the BPT diagram.In order to explain the unique properties of the misclassified broad line AGN SDSS J1042-0018,two methods are proposed,the star-forming contributions and the compressed narrow emission line regions with high electron densities near to critical densities of forbidden emission lines.Fortunately,the strong star-forming contributions can be preferred in SDSS J1042-0018.The misclassified broad line AGN SDSS J1042-0018,well explained by star-forming contributions,could provide further clues on the applications of BPT diagrams to the normal broad line AGNs.

Superluminal Motion and Polarization in Blazars

A relativistic beaming model has been successfully used to explain the observed properties of active galactic nuclei (AGNs). In this model there are two emission components, a boosted one and an unbeamed one, shown up in the radio band as the core and lobe components. The luminosity ratio of the core to the lobe is defined as the core-dominance parameter (R = (LCore/LLobe)). The de-beamed radio luminosity (Ljetdb) in the jet is assumed to be proportional to the unbeamed luminosity (Lub) in the co-moving frame, i.e., f = (Ljetdb/Lub), and f is determined in our previous paper. We further discuss the relationship between BL Lacertae objects (BLs) and flat spectrum radio quasars (FSRQs), which are subclasses of blazars with different degrees of polarization, using the calculated values of the ratio f for a sample of superluminal blazars. We found 1) that the BLs show smaller averaged Doppler factors and Lorentz factors, larger viewing angles and higher core-dominance parameters than do the FSRQs, and 2) that in the polarization-core dominance parameter plot (P-log R) the BLs and FSRQs occupy a scattered region, but in a revised plot (log (P/c(m)) ? log R), they gather around two different lines, suggesting that they have some different intrinsic properties.

Relations between the IR-UV-X-ray Continuum and Emission Lines for a Large Composite Sample of Narrow Line and Normal Seyfert 1 Galaxies

We report on our research on the UV, optical line parameters and the infrared through UV to soft X-ray continuum parameters for a composite sample of narrow line and normal Seyfert 1 galaxies. The strong correlations among the line width of HB, optical line strength of Fell and the soft X-ray slope are confirmed. We found no correlations between the UV line parameters, the equivalent widths of Lya and CIV and their ratio on one hand and the optical line parameters on the other. The UV and X-ray luminosities strongly correlate with the line widths of HB and the Fe II/HB ratio. No significant correlation is found between the infrared-soft X-my continuum slope aix and the line width of HB.

Black holes as the source of dark energy:A stringent test with high-redshift JWST AGNs

Studies have proposed that there is evidence for cosmological coupling of black holes(BHs)with an index of k≈3;hence,BHs serve as the astrophysical source of dark energy.However,the data sample is limited for the redshifts of≤2.5.In recent years,the James Webb Space Telescope(JWST)has detected many high-redshift active galactic nuclei(AGNs)and quasars.Among the JWST NIRSpec-/NIRCam-resolved AGNs,three are determined to be in early-type host galaxies with a redshift of z~4.5-7.However,their M_(*)and MBH are in tension with the predicted cosmological coupling of black holes with k=3 at a confidence level of~2σ,which challenges the hypothesis that BHs serve as the origin of dark energy.Future work on high-redshift AGNs using the JWST will further assess such a hypothesis by identifying more early-type host galaxies in the higher mass range.

Investigating jet physical properties of Fermi blazars with broad-line emissions

Relativistic outflows often exhibit extreme observational characteristics due to beaming effects, which makes measuring their jet power a challenging task. Although the spectral energy distribution(SED) obtained from multi-wavelength data can constrain the physical parameters of these jets, accurately estimating the Doppler factor remains difficult. To address this challenge, we assemble a comprehensive sample containing available SEDs of synchrotron and inverse Compton(IC) components, monochromatic luminosity, and broad-line region(BLR) emissions. We employ a parabolic equation to fit the synchrotron radiation SEDs,constraining jet physical parameters within the framework of a one-zone leptonic model. Our study delves into the jet properties and Doppler factor estimations, yielding the following key findings:(1) The fitting results of SED data for the entire sample reveal normal distributions of jet physical parameters for two subclasses of blazars.(2) Correlation analysis demonstrates that synchrotron peak luminosity exhibits a proportional relationship with both the radio and the γ-ray luminosities.(3) We introduce a novel method for estimating Doppler factors, which uncovers discrepancies between Doppler factors from this work and others from different techniques.

Estimation of inverse Compton peak frequency for 4FGL Blazars

This study uses a parabolic equation to fit the Inverse Compton (IC) spectral component of 3743 blazars (794 FSRQs,1432 BLLacs,and 1517 BCUs) from the 4FGL-DR3 catalog.Some mutual correlations are investigated,and a Bayesian classification is performed to the IC peak frequencies.Our analyses draw the following conclusions:(1) The Bayesian classification shows two components with a dividing boundary of log(v_(p)^(IC)/Hz)pIC=22.9.Therefore,the 3743 blazars are divided into low IC peak frequency(LCP) blazars and high IC peak frequency (HCP) blazars.(2) A strong linear correlation exists between IC peak frequency(logv_(p)^(IC)) and γ-ray photon spectral index (Γ).The IC peak frequency can be estimated by an empirical relation logv_(p)^(IC)=–4.5·Γ+32.8 for BL Lacs and logv_(p)^(IC)=4.0+31.4pICfor FSRQs,which is consistent with the result by Abdo et al.(3) The ICspectral curvature and IC peak frequency are not as closely related as the synchrotron curvature and the synchrotron peak frequency.(4) An anti-correlation exists between IC peak frequency and IC peak luminosity,implying that as the IC peak frequency in the γ-ray band decreases,the source becomes more luminous.The beaming effect is stronger for the source with a lower IC peak frequency.(5) Positive correlations exist between IC and synchrotron components for both peak frequencies and peak fluxes,but no clear correlation exists between IC curvature and synchrotron curvature.

The central black hole masses for the γ-ray loud blazars

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST) provides an increase in sensitivity and has detected rapid variability of gamma-ray sources.The variability time scales detected from the gamma-ray loud blazars by LAT and EGRET,and gamma-ray luminosity are used to estimate the central black hole masses.In this work,we find that the lower limits of central black hole masses are in a range of (0.3-24)×107M⊙,which are compared with those obtained by other authors.Our results are consistent with other authors' results.Also,the Lorentz factor,Γ,and the propagation angle,θ,are obtained for 18 blazars for which superluminal motions are known.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.