arXiv subjects

Shuang-Liang Li

Publications and source records attributed to Shuang-Liang Li.

At least 19 recordsLinked to original sources

arXiv2026

Quasi-periodic Eruptions from Recurrent Satellite Black Hole Transits through Magnetized Galactic Nucleus Accretion Disks

Quasi-periodic eruptions (QPEs) are recurrent soft X-ray flares from galactic nuclei, but their origin remains uncertain. The delayed ultraviolet (UV) counterpart detected in ZTF19acnskyy provides a new constraint on viable models. We present a two-channel model in which a satellite black hole (sBH) repeatedly crosses a nuclear accretion disk threaded by a large-scale magnetic field. Gravitational focusing and dynamical drag generate hot, optically thick ejecta whose expansion and photon diffusion power the soft X-ray QPE. For fiducial Bondi-scale parameters, the model yields a characteristic X-ray duration of $\sim10^3\ \mathrm{s}$ and luminosity of $\sim10^{42}\ \mathrm{erg\,s^{-1}}$. For ZTF19acnskyy, the model reproduces the observed day-scale X-ray duration and energetics. Simultaneously, the sBH motion compresses and bends the background magnetic field, triggering in-disk reconnection. The reconnection channel provides the energy budget and photon-diffusion delay required for the variable UV component. Unfavorable magnetic fields or diffusion times longer than the QPE recurrence period can weaken or smear out the UV signal, potentially explaining the lack of clear UV counterparts in other QPE sources.

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arXiv2026

The physical mechanism for two rapid changing-look AGNs: SDSS J0225+0030 and SDSS J1723+5504

SDSS J0225+0030 and SDSS J1723+5504 are two turn-on changing-look active galactic nuclei (CL AGNs) with transition timescales shorter than one year. Such short timescales pose a challenge for the current physical models of CL AGNs. We investigate this issue by exploring two possible mechanisms in this work. First, we consider the effect of a large-scale magnetic field on the viscous timescale, which can increase the radial velocity of the accretion disk. However, it is found that the timescale given by this model remains significantly longer than one year. Second, we improve the model of \citet{2025ApJ...988..207L}, which proposed that the inner thin disk in the bright state may form through the collapse of an advection-dominated accretion flow (ADAF) in the dim state, rather than being replaced by the advection of the outer thin disk. We re-estimate the transition radius $R_{\rm tr}$ between the inner ADAF and the outer thin disk through the observed variation of optical flux between the bright state and dim state. It is found that $R_{\rm tr}$ can be significantly reduced in these two objects owing to the lower gas temperature in the inner disk region (of the order of $10^4$ K), resulting from their large black hole masses ($\sim 10^9 M_{\odot}$) and small Eddington-scaled mass accretion rates ($\sim 0.01$). The cooling timescales given by the revised model in these two objects are found to be comparable to the observed transition timescales.

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arXiv2025

Disk Instability Model for Quasi-Periodic Eruptions: Investigating Period Dispersion and Peak Temperature

Quasi-periodic eruptions (QPEs) are a class of X-ray repeating burst phenomena discovered in recent years. Many models have been proposed to study this phenomenon, there remains significant debate regarding the physical origin of QPEs. In our previous work, we developed a disk instability model with a large-scale magnetic field and successfully reproduced the light curves and spectral characteristics of several QPE sources. We further investigate the model in this work, aiming to explain two key observational features: the dispersion in eruption periods and the peak temperatures during eruptions. The model reveals critical thresholds ($\dot{M}_{\rm crit}$, $β_{1,\rm crit}$) that separate systems into stable regimes with minimal period variations and unstable regimes where periods are highly sensitive to accretion rate and magnetic field parameter, while peak temperatures remain nearly constant across the parameter space. This framework successfully explains both the regular eruptions observed in sources like GSN 069 and the stochastic behavior in sources like eRO-QPE1, and simultaneously accounting for the observed temperature stability during long-term QPEs evolution.

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arXiv2025

The physical mechanism of radio-quiet turn-on changing-look active galactic nuclei

It is suggested that the variation of mass accretion rate in accretion disk may be responsible for the occurrence of most changing-look active galactic nuclei (CL AGNs). However, the viscous timescale of a thin disk is far longer than the observed timescale of CL AGNs. Though this problem can be resolved by introducing the large-scale magnetic field, the mechanism for radio-quiet CL AGNs with weak/absent large-scale magnetic field remains a mystery. In this work, we assume that the thin accretion disk is collapsed from the inner advection-dominated accretion flow (ADAF) instead of substituting by the outer thin disk through advection. This idea is tested by comparing the cooling timescale ($t_{\rm cool}$) of an ADAF with the observed timescale ($t_{\rm tran}$) of turn-on CL AGNs. We compile a sample of 102 turn-on CL AGNs from the archived data and calculate the cooling timescale of an ADAF with the critical mass accretion rate based on some conventional assumptions. It is found that $t_{\rm cool}$ is much shorter than $t_{\rm tran}$ in most of the CL AGNs, which validates our assumption though $t_{\rm cool}$ is not consistent with $t_{\rm tran}$ ($t_{\rm cool}<t_{\rm tran}$). However, this is reasonable since most of the CL AGNs were observed only two times, indicating that the observed timescale $t_{\rm tran}$ is the maximum value because the changing-look can indeed happen before the second observation.

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arXiv2025

Reverberation evidence for Stream Collision and Delayed Disk Formation in Tidal Disruption Events

When a star passes through the tidal disruption radius of a massive black hole (BH), it can be torn apart by the tidal force of the BH, known as the Tidal Disruption Event (TDE). Since the observed UV/optical luminosity significantly exceeds the predictions of the compact disk model in classical TDE theory, two competing models, stream collision and envelope reprocessing, have been proposed to address this discrepancy. To distinguish between these models, we investigate the continuum reverberation behaviors for $\sim$30 TDEs with high-quality multi-band light curves. We found that over half of them exhibit a positive lag by a few days in UV/optical bands, indicating that their inferred sizes are significantly larger than the envelope sizes in reprocessing. Moreover, X-ray emissions not only significantly delay relative to the primary UV/optical peak but also lag behind the rebrightening bump by up to several tens of days, completely different from the X-ray illumination reprocessing. Additionally, the anti-correlated UV-optical continuum in ASASSN-15lh further disfavors the reprocessing scenario. In contrast, the model of stream collisions, combined with delayed accretion disk formation, can provide a unified explanation for the diverse TDE observations, e.g., the optical/X-ray population, the frequently observed rebrightening bump. This model describes a unification scheme wherein the UV/optical emission originates from stream collisions during the early-stage of TDE evolution and gradually transitions to being dominated by accretion disk with detectable X-ray emission in the late stage. After transitioning to a quiescent state, recurrent flares may be observed in some cases, possibly related to repeating partial TDEs.

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arXiv2024

Do all the quasars and high-excitation radio galaxies (HERGs) in the 3CRR catalog contain a magnetically arrested disk (MAD)?

Based on the magnetization, an accretion disk with large-scale magnetic field can be separated into either standard and normal evolution (SANE) or magnetically arrested disk (MAD), which are difficult to identify from observations. It is still unclear whether all the radio-loud active galactic nuclei (RLAGNs) with a thin disk and strong radio emissions contain a MAD. We investigate this issue by utilizing the 3CRR catalog. We compile a sample of 35 quasars and 14 high-excitation radio galaxies powered by a thin accretion disk. In order to consistently compare with the MAD sample given by Li et al. (2022), the optical-UV emissions of our sample are all detected by the Hubble Space Telescope (HST). It is found that the average X-ray luminosity ($L_{\rm X}$) of our sample is about 5.0 times higher than that of radio-quiet AGNs (RQAGNs) with matching optical-UV luminosity ($L_{\rm UV}$), in general accord with the factor of 4.5 times in MAD sample within the uncertainty. The relationship between radio (5~GHz) and X-ray (2 keV) luminosities in the 3CRR sources is also found to be consistent with the MAD sample. Furthermore, the jet efficiencies of 3CRR sources are consistent with those from the GRMHD simulations of MAD. Therefore, we suggest that probably all the quasars and at least a fraction of high-excitation radio galaxies in the 3CRR catalog, and perhaps all the RLAGNs with strong radio emissions contain a MAD.

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arXiv2023

Time-dependent global simulations of a thin accretion disc: the effects of magnetically-driven winds on thermal instability

According to the standard thin disc theory, it is predicted that the radiation-pressure-dominated inner region of a thin disc is thermally unstable, while observations suggest that it is common for a thin disc of more than 0.01 Eddington luminosity to be in a thermally stable state. Previous studies have suggested that magnetically driven winds have the potential to suppress instability. In this work, we implement one-dimensional global simulations of the thin accretion disc to study the effects of magnetically driven winds on thermal instability. The winds play a role in transferring the angular momentum of the disc and cooling the disc. When the mass outflow rate of winds is low, the important role of winds is to transfer the angular momentum and then shorten the outburst period. When the winds have a high mass outflow rate, they can calm down the thermal instability. We also explore the parameter space of the magnetic field strength and the mass loading parameter.

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arXiv2023

Application of the disk instability model to all Quasi-Periodic Eruptions

After the first quasi-periodic eruptions (QPEs, GSN069) was reported in 2019, four other sources have been identified as QPEs or its candidate. However, the physics behind QPEs is still unclear so far, though several models have been proposed. Pan et al. (2022) proposed an instability model for the accretion disk with magnetically driven outflows in the first QPEs GSN 069, which is able to reproduce both the light curve and the evolution of spectrum fairly well. In this work, we exploit this model to all the QPEs. We imporve the calculations of the spectrum of disk by introducing a hardening factor, which is caused by the deviation of opacity from the blackbody. We find that the light curves and evolution of the spectra of the four QPEs or candidate can all be well reproduced by our model calculations.

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arXiv2022

Constraining X-ray emission of magnetically arrested disk (MAD) by radio-loud AGNs with extreme ultraviolet (EUV) deficit

Aims. Active galactic nuclei (AGNs) with EUV deficit are suggested to be powered by a MAD surrounding the black hole, where the slope of EUV spectra ($α_{\rm EUV}$) is found to possess a well positive relationship with the jet efficiency. In this work, we investigate the properties of X-ray emission in AGNs with EUV deficit for the first time. Methods. We construct a sample of 15 objects with EUV deficit to analyse their X-ray emission. The X-ray luminosity in 13 objects are newly processed by ourself, while the other 2 sources are gathered from archival data. Results. It is found that the average X-ray flux of AGNs with EUV deficit are 4.5 times larger than that of radio-quiet AGNs (RQAGNs), while the slope of relationship between the optical-UV luminosity ($L_{\rm UV}$) and the X-ray luminosity ($L_{\rm X}$) is found to be similar with that of RQAGNs. For comparison, the average X-ray flux of radio-loud AGNs (RLAGNs) without EUV deficit is about 2-3 times larger than that of RQAGNs. A strong positive correlation between $α_{\rm EUV}$ and radio-loudness ($R_{\rm UV}$) is also reported. However, there is no strong relationship between $L_{\rm X}$ and the radio luminosity ($L_{\rm R}$). Conclusions. Both the excess of X-ray emission of RLAGNs with EUV deficit and the strong $α_{\rm EUV}$-$R_{\rm UV}$ relationship can be qualitatively explained with MAD scenario, which can help to constrain the theoretical model of MAD.

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arXiv2022

A disk instability model for the quasi-periodic eruptions of GSN 069

GSN 069 is a recently discovered QPE (Quasi-periodic eruptions) source recurring about every 9 hours. The mechanism for the QPEs of GSN 069 is still unclear so far. In this work, a disk instability model is constructed to explain GSN 069 based on Pan et al. (2021) (PLC21), where the authors proposed a toy model for the repeating changing-look (CL) active galactic nuclei (AGN). We improve the work of PLC21 by including a non-zero viscous torque condition on the inner boundary of disk and adopting a general form for the viscous stress torque in Kerr metric. It is found that the 0.4-2 keV light curves, the light curves at different energy bands and the phase-resolved X-ray spectrum of GSN 069 can all be qualitatively reproduced by our model. Furthermore, the profiles of light curve in QPEs can be significantly changed by the parameter μin viscous torque equation, which implies that our model may also be applied to other QPEs.

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arXiv2021

The origin of X-ray emission in 3CRR sources: hints from mid-infrared Spitzer observations

Whether X-ray emission in radio-loud (RL) active galactic nuclei (AGNs) originates from disk coronae or jets is still under debate. For example, the positive relationships in radio-quiet (RQ) AGNs (such as the optical to X-ray spectral index $α_{\rm {OX}}$ and Eddington ration $λ_{\rm {O}}$ as well as the X-ray photon index $Γ$ and $λ_{\rm {O}}$) are not detected in RLAGNs. We intend to further investigate this issue in this work. A sample of 27 luminous sources (including 16 quasars and 11 high-excitation radio galaxies) was selected from the 3CRR catalog to reinvestigate the origin of X-ray emission in RLAGNs, where the X-ray and mid-infrared fluxes are observed by Chandra/XMM-Newton and Spitzer, respectively. It is found for the first time that there is a significant relationship between the mid-infrared to X-ray spectral index $α_{\rm {IX}}$ and $λ_{\rm {IR}}$ for whole sample, while there is no relationship between $α_{\rm {OX}}$ and $λ_{\rm {O}}$ in quasars. There are strong positive relationships between both $L_{\rm {R}}$-$L_{\rm {X}}$ and $L_{\rm {UV}}$-$L_{\rm {X}}$ panels, which can be well fitted by the disk-corona model. However, there is no significant relationship between $Γ$ and $λ_{\rm {IR}}$. The possible reason is related to the effects of the large-scale magnetic field in RLAGNs. We suggest that the X-ray emission in high-excitation RLAGNs originates from a disk-corona system.

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arXiv2021

The effects of large-scale magnetic fields on the model for repeating changing-look AGNs

Periodic outbursts are observed in several changing-look (CL) active galactic nuclei (AGNs). \citet{sniegowska_possible_2020} suggested a model to explain the repeating CL in these AGNs, where the periodic outbursts are triggered in a narrow unstable zone between an inner ADAF and outer thin disk. In this work, we intend to investigate the effects of large-scale magnetic fields on the limit cycle behaviors of CL AGNs. The winds driven by magnetic fields can significantly change the structure of thin disk by taking away the angular momentum and energy of the disk. It is found that the period of outburst in repeating CL AGNs can be substantially reduced by the magnetic fields. Conversely, if we keep the period unchanged, the outburst intensity can be raised for several times. These results can help to explain the observational properties of multiple CL AGNs. Besides the magnetic fields, the effects of transition radius $R_{\rm tr}$, the width of transition zone $ΔR$ and Shakura-Sunyaev parameter $α$ are also explored in this work.

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arXiv2019

A nearby luminous AGN sample optically selected from Hubble Space Telescope (HST)

In this work, a nearby luminous AGN sample is selected from HST, where only sources with both X-ray emission observed by \textit{Chandra/XMM-Newton} and radio flux detected by VLA/VLBA/VLBI/MERLIN are adopted to keep high precision. We get a sample of 30 luminous AGNs finally, which consist of 11 RLAGN and 19 RQAGN. It is found that the relationship between $R_{\rm {UV}}$ and $α_{\rm {ox}}$, which was firstly reported by Li & Xie (2017) in LLAGN, and other relationships are all absent in RLAGN, probably due to the complex physical process therein. Our results indicate that the X-ray emission from jet should play an important role in RLAGN and further support the transition of accretion mode between LLAGN and RLAGN. On the other hand, the traditional relationships in RQAGN, such as $α_{\rm {ox}}$ and $λ$, $Γ$ and $λ$, are found to be well consistent with previous works.

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arXiv2018

Black Hole Fundamental Plane in Low-Excitation Radio Galaxies

The radio-X-ray slope in the fundamental plane of radio-loud active galactic nuclei (AGNs) is found to be steeper compared with that of radio-quiet AGNs in previous works. In this work, we reinvestigate the fundamental plane in radio-loud AGNs by compiling a sample of 13 low-excitation radio galaxies (LERG) from the 3CR radio galaxies, for the reason that the accretion mode in LERG is believed to be a radiatively inefficient accretion flow. All the sources in our sample possess the data available at both the 5 GHz core radio luminosity detected by VLA/VLBI/VLBA and the core X-ray luminosity detected by Chandra/XMM-Newton. Surprisingly, we find the slope in the fundamental plane ($\log L_{\rm R}=0.52 \log L_{\rm X}+ 0.84 \log M_{\rm BH} + 10.84$) of LERG is well consistent with that reported by \citet{m2003}. However, the normalization is found to be shifted by about 0.7 dex, which can be due to the difference on magnetic field strength in different objects. A shallower slope of $L_{\rm R}-L_{\rm X}$ relation ($L_{\rm R}\sim L_{\rm X}^{0.63}$) is also given by our sample, which demonstrates that the X-ray emission in LERG may come from accretion disc instead of jets as suggested by previous works.

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arXiv2017

A strong negative correlation between radio loudness $R_{\rm UV}$ and optical-to-X-ray spectral index $α_{\rm ox}$ in low-luminosity AGNs

It has been argued for years that the accretion mode changes from bright active galactic nuclei (AGNs) to low-luminosity AGNs (LLAGNs) at a rough dividing point of bolometric Eddington ratio $λ\sim 10^{-2}$. In this work, we strengthen this scenario through investigation of the relationship between the radio loudness $R_{\rm UV}$ and the optical-to-X-ray spectral index $α_{\rm ox}$ in LLAGNs with $10^{-6} \lesssim λ\lesssim 10^{-3}$. We compile from literature a sample of 32 LLAGNs, consisting 18 LINERs and 14 low Eddington ratio Seyfert galaxies, and observe a strong negative $R_{\rm UV}$--$α_{\rm ox}$ relationship, with large scatter in both $R_{\rm UV}$ and $α_{\rm ox}$. We further demonstrate that this negative correlation, and the additional two negative relationships reported in literature ($R_{\rm UV}$--$λ$ and $α_{\rm ox}$--$λ$ correlations), can be understood consistently and comprehensively under the truncated accretion--jet model, the model that has been applied successfully applied to LLAGNs. We argue that the scatter in the observations are (mainly) due to the spread in the viscosity parameter $α$ of a hot accretion flow, a parameter that potentially can serve as a diagnose of the strength and/or configuration of magnetic fields in accretion flows.

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arXiv2016

An Accretion Disc-Irradiation Hybrid Model for The Optical/UV Variability in Radio-Quiet Quasars

The optical/ultraviolet (UV) variability of quasars has been discovered to be correlated with other quasar properties, such as luminosity, black hole mass and rest-frame wavelength. However,the origin of variability has been a puzzle so far. In this work, we upgrade the accretion disc model (Li & Cao 2008), which assumed the variability is caused by the change of global mass accretion rate, by constraining the disc size to match the viscous timescale of accretion disc to the variability timescale observed and by including the irradiation/X-ray reprocessing to make the emitted spectrum become steeper. We find this hybrid model can reproduce the observed bluer-when-brighter trend quite well, which is used to validate the theoretical model by several works recently. The traditional correlation between the variability amplitude and rest-frame wavelength can also be well fitted by our model. In addition, a weak positive correlation between variability amplitude and black hole mass is present, qualitatively consistent with recent observations.

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arXiv2015

State transitions triggered by inverse magnetic field: probably applied in high-mass X-ray binaries?

Previous works suggested that the state transitions in an X-ray binary can be triggered by accreting inverse magnetic field from its companion star. A key point of this mechanism is the accretion and magnification of large-scale magnetic fields from outer boundary of a thin disk. However, how such a process can be realized is still an open question. In this work, we check this issue in a realistic X-ray binary system. According to our calculations, a quite strong initial magnetic field $B\sim 10^2-10^3$ G is required in order to assure that the large-scale magnetic field can be effectively dragged inward and magnified with the accretion of gas. Thus, such a picture probably can be present in high-mass X-ray binaries possessing strong stellar magnetic field, e.g., Cyg X-1.

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arXiv2014

The high efficiency jets magnetically accelerated from a thin disk in powerful lobe-dominated FRII radio galaxies

A maximum jet efficiency line $R\sim 25$ ($R=L_{\rm jet}/L_{\rm bol}$), found in FRII radio galaxies by Fernandes et al., was extended to cover the full range of jet power by Punsly. Recent general relativistic magnetohydrodynamic (GRMHD) simulations on jet formation mainly focused on the enhancement of jet power. In this work, we suggest that the jet efficiency could be very high even for conventional jet power if the radiative efficiency of disk were much smaller. We adopt the model of a thin disk with magnetically driven winds to investigate the observational high efficiency jets in FRII radio galaxies. It is found that the structure of a thin disk can be significantly altered by the feedback of winds. The temperature of disk gradually decreases with increasing magnetic field; the disk density, surface density and pressure also change enormously. The lower temperature and higher surface density in inner disk result in the rapid decrease of radiative efficiency. Thus, the jet efficiency is greatly improved even the jet power is conventional. Our results can explain the observations quite well. A theoretical maximum jet efficiency $R \sim 1000$ suggested by our calculations is large enough to explain all the high jet efficiency in observations even considering the episodic activity of jets.

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