arXiv subjects

Yan-Rong Li

Publications and source records attributed to Yan-Rong Li.

At least 55 records · Page 3Linked to original sources

arXiv2022

Supermassive Black Hole and Broad-line Region in NGC~5548: Results from Five-season Reverberation Mapping

NGC 5548 is one of the active galactic nuclei (AGN) selected for our long-term spectroscopic monitoring with the Lijiang 2.4~m telescope, aiming at investigating the origin and evolution of the broad-line regions (BLRs), accurately measuring the mass of the supermassive black holes (SMBHs), and understanding structure and evolution of the AGN. We have performed five-season observations for NGC~5548 with the median sampling interval ranging from 1.25 to 3 days. The light curves of the 5100~Å continuum and broad emission lines are measured after subtracting contamination of the host galaxy starlight. The time lags of the broad He~{\sc ii}, He~{\sc i}, H$γ$, and H$β$ lines with respect to the 5100~Å continuum are obtained for each season and their mean time lags over the five seasons are 0.69, 4.66, 4.60, 8.43 days, respectively. The H$γ$ and H$β$ velocity-resolved lag profiles in the seasons of 2015, 2018, 2019, and 2021 are constructed, from which an ``M-shaped'' structure is found in 2015 but disappears after 2018. Our five-season reverberation mapping (RM) yields an averaged virial SMBH mass of $M_\bullet/10^7M_\odot=14.22$, with a small standard deviation of $1.89$. By combining the previous 18 RM campaigns and our five-season campaign for NGC~5548, we find that there exists a time lag of 3.5~years between the changes in the BLR size and optical luminosity. In addition, we also construct the BLR radius$-$luminosity relation and the virial relation for NGC~5548.

astro-ph.GA↗

arXiv2022

The LSST era of supermassive black holes accretion-disk reverberation mapping

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will detect an unprecedentedly large sample of actively accreting supermassive black holes with typical accretion disk (AD) sizes of a few light days. This brings us to face challenges in the reverberation mapping (RM) measurement of AD sizes in active galactic nuclei (AGNs) using interband continuum delays. We examine the effect of LSST cadence strategies on AD RM using our metric AGNTimeLagMetric. It accounts for redshift, cadence, the magnitude limit, and magnitude corrections for dust extinction. Running our metric on different LSST cadence strategies, we produce an atlas of the performance estimations for LSST photometric RM measurements. We provide an upper limit on the estimated number of quasars for which the AD time lag can be computed within 0 1000 sources in each Deep Drilling field (DDF, 10 sq. deg) in any filter, with the redshift distribution of these sources peaking at z~1. We find the LSST observation strategies with a good cadence (~ 5 days) and a long cumulative season (~9 yr), as proposed for LSST DDF, are favored for the AD size measurement. We create synthetic LSST light curves for the most suitable DDF cadences and determine RM time lags to demonstrate the impact of the best cadences based on the proposed metric.

astro-ph.IM↗

arXiv2022

Revisiting the Continuum Reverberation Lags in the AGN PKS 0558-504

We present a revised analysis of the photometric reverberation mapping campaign of the narrow-line Seyfert 1 galaxy PKS 0558-504 carried out with the Swift Observatory during 2008--2010. Previously, Gliozzi et al.\ found using the Discrete Correlation Function (DCF) method that the short-wavelength continuum variations lagged behind variations at longer wavelengths, the opposite of the trend expected for thermal reprocessing of X-rays by the accretion disc, and they interpreted their results as evidence against the reprocessing model. We carried out new DCF measurements that demonstrate that the inverted lag-wavelength relationship found by Gliozzi et al.\ resulted from their having interchanged the order of the driving and responding light curves when measuring the lags. To determine the inter-band lags and uncertainties more accurately, we carried out new measurements with four independent methods. These give consistent results showing time delays increasing as a function of wavelength, as expected for the disc reprocessing scenario. The slope of the re-analysed delay spectrum appears to be roughly compatible with the predicted $τ\propto λ^{4/3}$ relationship for reprocessing by an optically thick and geometrically thin accretion disc, although the data points exhibit a large scatter about the fitted power-law trend.

astro-ph.GA↗

arXiv2022

Monitoring AGNs with H$β$ Asymmetry. III. Long-term Reverberation Mapping Results of 15 Palomar-Green Quasars

In this third paper of the series reporting on the reverberation mapping (RM) campaign of active galactic nuclei with asymmetric H$β$ emission-line profiles, we present results for 15 Palomar-Green (PG) quasars using spectra obtained between the end of 2016 to May 2021. This campaign combines long time spans with relatively high cadence. For 8 objects, both the time lags obtained from the entire light curves and the measurements from individual observing seasons are provided. Reverberation mapping of 9 of our targets has been attempted for the first time, while the results for 6 others can be compared with previous campaigns. We measure the H$β$ time lags over periods of years and estimate their black hole masses. The long duration of the campaign enables us to investigate their broad line region (BLR) geometry and kinematics for different years by using velocity-resolved lags, which demonstrate signatures of diverse BLR geometry and kinematics. The BLR geometry and kinematics of individual objects are discussed. In this sample, the BLR kinematics of Keplerian/virialized motion and inflow is more common than outflow.

astro-ph.GA↗

arXiv2022

Accretion Disk Size Measurements of Active Galactic Nuclei Monitored by the Zwicky Transient Facility

We compile a sample of 92 active galactic nuclei (AGNs) at z<0.75 with $gri$ photometric light curves from the archival data of the Zwicky Transient Facility and measure the accretion disk sizes via continuum reverberation mapping. We employ Monte Carlo simulation tests to assess the influences of data sampling and broad emission lines and select out the sample with adequately high sampling cadences (3 days apart in average) and minimum contaminations of broad emission lines. The inter-band time delays of individual AGNs are calculated using the interpolated cross-correlation function and then these delays are fitted with a generalized accretion disk model, in which inter-band time delays are a power function of wavelength, black hole mass, and luminosity. A Markov-chain Monte Carlo method is adopted to determine the best parameter values. Overall the inter-band time delays can be fitted with the $τ\ \propto λ^{4/3}$ relation as predicted from a steady-state, optically thick, geometrically thin accretion disk, however, the yielded disk size is systematically larger than expected, although the ratio of the measured to theoretical disk sizes depend on using the emissivity -- or responsivity -- weighted disk radius. These results are broadly consistent with previous studies, all together raising a puzzle about the "standard" accretion disk model.

astro-ph.GA↗

arXiv2022

Spectroastrometry and Reverberation Mapping: the Mass and Geometric Distance of the Supermassive Black Hole in the Quasar 3C 273

The quasar 3C 273 has been observed with infrared spectroastrometry (SA) on broad Pa$α$ line and optical reverberation mapping (RM) on broad H$β$ line. SA delivers information about the angular size and structure of the Pa$α$ broad-line region (BLR), while RM delivers information about the physical size and structure of the H$β$ BLR. Based on the fact that the two BLRs share the mass of the supermassive black hole (SMBH) and viewing inclination, a combination of SA and velocity-resolved RM (SARM) thereby allows us to simultaneously determine the SMBH mass and geometric distance through dynamically modeling the two BLRs. We construct a suite of dynamical models with different geometric configurations and apply a Bayesian approach to obtain the parameter inferences. Overall the obtained masses and distances are insensitive to specific BLR configurations but more or less depend on parameterizations of the vertical distributions. The most probable model, chosen in light of the Bayes factor, yields an angular-size distance of $\log\,(D_{\rm A}/{\rm Mpc}) = 2.83_{-0.28}^{+0.32}$ and SMBH mass of $\log\,(M_\bullet/M_\odot)=9.06_{-0.27}^{+0.21}$, which agrees with the relationships between SMBH masses and bulge properties. The BLRs have an inclination of $5_{-1}^{+1}$ degrees, consistent with that of the large-scale jet in 3C 273. Our approach reinforces the capability of SARM analysis to measure SMBH mass and distance of AGNs even though SA and RM observations are undertaken with different emission lines and/or in different periods.

astro-ph.GA↗

arXiv2021

A Pixon-Based Method for Reverberation-mapping Analysis in Active Galactic Nuclei

We present an alternative method for reconstructing a velocity-delay map in reverberation mapping (RM) based on the pixon algorithm initially proposed for image reconstruction by Pina & Puetter (1993). The pixon algorithm allows for a variable pixon basis to adjust resolution of each image pixel according the information content in that pixel, which therefore enables the algorithm to make the best possible use of measured data. The final optimal pixon basis functions would be those that minimize the number of pixons while still providing acceptable descriptions to data within the accuracy allowed by noises. We adapt the pixon algorithm to RM analysis and develop a generic framework to implement the algorithm. Simulation tests and comparisons with the widely used maximum entropy method demonstrate the feasibility and high performance of our pixon-based RM analysis. This paper serves as an introduction to the framework and the application to velocity-unresolved RM. An extension to velocity-resolved cases will be presented in a companion paper.

astro-ph.IM↗

arXiv2021

Search for Continuous Gravitational Wave Signals in Pulsar Timing Residuals: A New Scalable Approach with Diffusive Nested Sampling

Detecting continuous nanohertz gravitational waves (GWs) generated by individual close binaries of supermassive black holes (CB-SMBHs) is one of the primary objectives of pulsar timing arrays (PTAs). The detection sensitivity is slated to increase significantly as the number of well-timed millisecond pulsars will increase by more than an order of magnitude with the advent of next-generation radio telescopes. Currently, the Bayesian analysis pipeline using parallel tempering Markov chain Monte Carlo has been applied in multiple studies for CB-SMBH searches, but it may be challenged by the high dimensionality of the parameter space for future large-scale PTAs. One solution is to reduce the dimensionality by maximizing or marginalizing over uninformative parameters semi-analytically, but it is not clear whether this approach can be extended to more complex signal models without making overly simplified assumptions. Recently, the method of diffusive nested (DNest) sampling shown the capability of coping with high dimensionality and multimodality effectively in Bayesian analysis. In this paper, we apply DNest to search for continuous GWs in simulated pulsar timing residuals and find that it performs well in terms of accuracy, robustness, and efficiency for a PTA including $\mathcal{O}(10^2)$ pulsars. DNest also allows a simultaneous search of multiple sources elegantly, which demonstrates its scalability and general applicability. Our results show that it is convenient and also high beneficial to include DNest in current toolboxes of PTA analysis.

astro-ph.IM↗

arXiv2021

Accretion-modified Stars in Accretion Disks of Active Galactic Nuclei: Gravitational Wave Bursts and Electromagnetic Counterparts from Merging Stellar Black Hole Binaries

The recent advanced LIGO/Virgo detections of gravitational waves (GWs) from stellar binary black hole (BBH) mergers, in particular GW190521, which is potentially associated with a quasar, have stimulated renewed interest in active galactic nuclei (AGNs) as factories of merging BBHs. Compact objects evolving from massive stars are unavoidably enshrouded by a massive envelope to form accretion-modified stars (AMSs) in the dense gaseous environment of a supermassive black hole (SMBH) accretion disk. We show that most AMSs form binaries due to gravitational interaction with each other during radial migration in the SMBH disk, forming BBHs inside the AMS. When a BBH is born, its orbit is initially governed by the tidal torque of the SMBH. Bondi accretion onto BBH at a hyper-Eddington rate naturally develops and then controls the evolution of its orbits. We find that Bondi accretion leads to efficient removal of orbital angular momentum of the binary, whose final merger produces a GW burst. Meanwhile, the Blandford-Znajek mechanism pumps the spin energy of the merged BH to produce an electromagnetic counterpart (EMC). Moreover, hyper-Eddington accretion onto the BBH develops powerful outflows and triggers a Bondi explosion, which manifests itself as a EMC of the GW burst, depending on the viscosity of the accretion flow. Thermal emission from Bondi sphere appears as one of EMCs. BBHs radiate GWs with frequencies $\sim 10^{2}\,$Hz, which are accessible to LIGO.

astro-ph.HE↗

arXiv2021

Reverberation Mapping of Two Luminous Quasars: the Broad-line Region Structure and Black Hole Mass

We report the results of a multi-year spectroscopic and photometric monitoring campaign of two luminous quasars, PG~0923+201 and PG~1001+291, both located at the high-luminosity end of the broad-line region (BLR) size-luminosity relation with optical luminosities above $10^{45}~{\rm erg~s^{-1}}$. PG~0923+201 is for the first time monitored, and PG~1001+291 was previously monitored but our campaign has a much longer temporal baseline. We detect time lags of variations of the broad H$β$, H$γ$, Fe {\sc ii} lines with respect to those of the 5100~Å continuum. The velocity-resolved delay map of H$β$ in PG~0923+201 indicates a complicated structure with a mix of Keplerian disk-like motion and outflow, and the map of H$β$ in PG~1001+291 shows a signature of Keplerian disk-like motion. Assuming a virial factor of $f_{\rm BLR}=1$ and FWHM line widths, we measure the black hole mass to be $118_{-16}^{+11}\times 10^7 M_{\odot}$ for PG~0923+201 and $3.33_{-0.54}^{+0.62}\times 10^7 M_{\odot}$ for PG~1001+291. Their respective accretion rates are estimated to be $0.21_{-0.07}^{+0.06} \times L_{\rm Edd}\,c^{-2}$ and $679_{-227}^{+259}\times L_{\rm Edd}\,c^{-2}$, indicating that PG~0923+201 is a sub-Eddington accretor and PG~1001+291 is a super-Eddington accretor. While the H$β$ time lag of PG~0923+201 agrees with the size-luminosity relation, the time lag of PG~1001+291 shows a significant deviation, confirming that in high-luminosity AGN the BLR size depends on both luminosity and Eddington ratio. Black hole mass estimates from single AGN spectra will be over-estimated at high luminosities and redshifts if this effect is not taken into account.

astro-ph.GA↗

arXiv2021

AGN STORM 2: I. First results: A Change in the Weather of Mrk 817

We present the first results from the ongoing, intensive, multi-wavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this AGN was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura-Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission line variability. The correlation recovers in the next 42 days of the campaign, as Mrk 817 enters a less obscured state. The short CIV and Ly alpha lags suggest that the accretion disk extends beyond the UV broad line region.

astro-ph.HE↗

arXiv2021

Geometric Distances of Quasars Measured by Spectroastrometry and Reverberation Mapping:Monte Carlo Simulations

Recently, GRAVITY onboard the Very Large Telescope Interferometer (VLTI) first spatially resolved the structure of the quasar 3C 273 with an unprecedented resolution of $\sim 10μ$as. A new method of measuring parallax distances has been successfully applied to the quasar through joint analysis of spectroastrometry (SA) and reverberation mapping (RM) observation of its broad line region (BLR). The uncertainty of this SA and RM (SARM) measurement is about $16\%$ from real data, showing its great potential as a powerful tool for precision cosmology. In this paper, we carry out detailed analyses of mock data to study impacts of data qualities of SA observations on distance measurements and establish a quantitative relationship between statistical uncertainties of distances and relative errors of differential phases. We employ a circular disk model of BLR for the SARM analysis. We show that SARM analyses of observations generally generate reliable quasar distances, even for relatively poor SA measurements with error bars of $40\%$ at peaks of phases. Inclinations and opening angles of BLRs are the major parameters governing distance uncertainties. It is found that BLRs with inclinations $\gtrsim 10^{\circ}$ and opening angles $\lesssim 40^{\circ}$ are the most reliable regimes from SARM analysis for distance measurements. Through analysis of a mock sample of AGNs generated by quasar luminosity functions, we find that if the GRAVITY/GRAVITY+ can achieve a phase error of $0.1^{\circ}$ per baseline for targets with magnitudes $K \lesssim 11.5$, the SARM campaign can constrain $H_0$ to an uncertainty of $2\%$ by observing $60$ targets.

astro-ph.GA↗

arXiv2020

Monitoring AGNs with Hβ Asymmetry. II. Reverberation Mapping of Three Seyfert Galaxies Historically Displaying Hβ Profiles with Changing Asymmetry: Mrk 79, NGC 3227, and Mrk 841

We report the results of reverberation mapping three bright Seyfert galaxies, Mrk 79, NGC 3227, and Mrk 841, from a campaign conducted from December 2016 to May 2017 with the Wyoming Infrared Observatory (WIRO) 2.3-meter telescope. All three of these targets have shown asymmetric broad H$β$ emission lines in the past, although their emission lines were relatively symmetric during our observations. We measured Hβ time lags for all three targets and estimated masses of their black holes -- for the first time in the case of Mrk 841. For Mrk 79 and NGC 3227, the data are of sufficient quality to resolve distinct time lags as a function of velocity and to compute two-dimensional velocity-delay maps. Mrk 79 shows smaller time lags for high-velocity gas but the distribution is not symmetric, and its complex velocity-delay map could result from the combination of both inflowing and outflowing Hβ emitting disks that may be part of a single larger structure. NGC 3227 shows the largest time lags for blueshifted gas and the two-dimensional velocity-delay map suggests a disk with some inflow. We compare our results with previous work and find evidence for different time lags despite similar luminosities, as well as evolving broad line region structures.

astro-ph.GA↗

arXiv2020

Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129

We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2m telescope from July 2017 to February 2020. Significant variations in the fluxes of the continuum and broad-emission lines, including H$β$ and He II, were observed in the first and third years, and clear time lags between them are measured. The broad H$β$ line profile consists of two Gaussian components: an intermediate-width H$β_{\rm IC}$ with a full width at half-maximum (FWHM) of 1964$\pm$18 $\rm km~s^{-1}$ and another very broad H$β_{\rm VBC}$ with a FWHM of 7570$\pm$83 $\rm km~s^{-1}$. H$β_{\rm IC}$ has long time lags of $\sim$40--60 days in the rest frame, while H$β_{\rm VBC}$ shows nearly zero time delay with respect to the optical continuum at 5100 Å. The velocity-resolved delays show consistent results: lags of $\sim$30--50 days at the core of the broad H$β$ line and roughly zero lags at the wings. H$β_{\rm IC}$ has a redshift of $\sim$400 $\rm km~s^{-1}$ which seems to be stable for nearly 30 years by comparing with archived spectra, and may originate from an infall. The root mean square (rms) spectrum of H$β_{\rm VBC}$ shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H$β_{\rm VBC}$ comes from a region associated with the part of the accretion disc that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total H$β$ line, and a virial factor of 1.5, we obtain a virial mass of $2.89_{-0.69}^{+0.60} \times10^7 M_{\odot}$ for the central black hole in this quasar.

astro-ph.GA↗

arXiv2020

Gravitational Test Beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole

The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.

gr-qc↗

arXiv2020

A parallax distance to 3C 273 through spectroastrometry and reverberation mapping

Distance measurements for extragalactic objects are a fundamental problem in astronomy and cosmology. In the era of precision cosmology, we urgently need better measurements of cosmological distances to observationally test the increasing $H_{0}$ tension of the Hubble constant measured from different tools. Using spectroastrometry, GRAVITY at The Very Large Telescope Interferometer successfully revealed the structure, kinematics and angular sizes of the broad-line region (BLR) of 3C 273 with an unprecedentedly high spatial resolution. Fortunately, reverberation mapping (RM) of active galactic nuclei (AGNs) reliably provides linear sizes of their BLRs. Here we report a joint analysis of spectroastrometry and RM observations to measure AGN distances. We apply this analysis to 3C 273 observed by both GRAVITY and an RM campaign,and find an angular distance of $551.5_{-78.7}^{+97.3}\, {\rm Mpc}$ and $H_{0}=71.5_{-10.6}^{+11.9}\,{\rm km\,s^{-1}\,Mpc^{-1}}$. Advantages of the analysis are 1) its pure geometrical measurements and 2) it simultaneously yields mass of the central black hole in the BLR. Moreover, we can conveniently repeat measurements of selected AGNs to efficiently reduce the statistical and systematic errors. Future observations of a reasonably sized sample ($\sim 30$ AGNs) will provide distances of the AGNs and hence a new way of measuring $H_{0}$ with a high precision $\left(\lesssim 3\%\right)$ to test the $H_{0}$ tension.

astro-ph.CO↗

arXiv2020

Untangling Optical Emissions of the Jet and Accretion Disk in the Flat-Spectrum Radio Quasar 3C 273 with Reverberation Mapping Data

3C 273 is an intensively monitored flat-spectrum radio quasar with both a beamed jet and blue bump together with broad emission lines. The coexistence of the comparably prominent jet and accretion disk leads to complicated variability properties. Recent reverberation mapping monitoring for 3C 273 revealed that the optical continuum shows a distinct long-term trend that does not have a corresponding echo in the Hbeta fluxes. We compile multi-wavelength monitoring data from the Swift archive and other ground-based programs and clearly find two components of emissions at optical wavelength. One component stems from the accretion disk itself and the other component can be ascribed to the jet contribution, which also naturally accounts for the non-echoed trend in reverberation mapping data. We develop an approach to decouple the optical emissions from the jet and accretion disk in 3C 273 with the aid of multi-wavelength monitoring data. By assuming the disk emission has a negligible polarization in consideration of the low inclination of the jet, the results show that the jet contributes a fraction of ~10% at the minimum and up to ~40% at the maximum to the total optical emissions. This is the first time to provide a physical interpretation to the "detrending" manipulation conventionally adopted in reverberation mapping analysis. Our work also illustrates the importance of appropriately analyzing variability properties in cases of coexisting jets and accretion disks.

astro-ph.HE↗

arXiv2020

Supermassive black holes with high accretion rates in active galactic nuclei. XI. Accretion disk reverberation mapping of Mrk 142

We performed an intensive accretion disk reverberation mapping campaign on the high accretion rate active galactic nucleus Mrk 142 in early 2019. Mrk 142 was monitored with the Neil Gehrels Swift Observatory for 4 months in X-rays and 6 UV/optical filters. Ground-based photometric monitoring was obtained from the Las Cumbres Observatory, Liverpool Telescope and Dan Zowada Memorial Observatory in ugriz filters and the Yunnan Astronomical Observatory in V. Mrk 142 was highly variable throughout, displaying correlated variability across all wavelengths. We measure significant time lags between the different wavelength light curves, finding that through the UV and optical the wavelength-dependent lags, $τ(λ)$, generally follow the relation $τ(λ) \propto λ^{4/3}$, as expected for the $T\propto R^{-3/4}$ profile of a steady-state optically-thick, geometrically-thin accretion disk, though can also be fit by $τ(λ) \propto λ^{2}$, as expected for a slim disk. The exceptions are the u and U band, where an excess lag is observed, as has been observed in other AGN and attributed to continuum emission arising in the broad-line region. Furthermore, we perform a flux-flux analysis to separate the constant and variable components of the spectral energy distribution, finding that the flux-dependence of the variable component is consistent with the $f_ν\proptoν^{1/3}$ spectrum expected for a geometrically-thin accretion disk. Moreover, the X-ray to UV lag is significantly offset from an extrapolation of the UV/optical trend, with the X-rays showing a poorer correlation with the UV than the UV does with the optical. The magnitude of the UV/optical lags is consistent with a highly super-Eddington accretion rate.

astro-ph.HE↗