arXiv subjects

Yunguo Jiang

Publications and source records attributed to Yunguo Jiang.

At least 19 recordsLinked to original sources

arXiv2026

Effective-potential classification of kink-antikink collision channels in the $\phi^8$ scalar field theory

We study kink-antikink collisions in a $(1+1)$-dimensional $\phi^8$ scalar field theory with multiple degenerate vacua. We derive soliton solutions for different vacuum structures labeled by $n=p_2/p_1$, and focus on the cases $n=2$ and $n=3$. We perform numerical simulations in all topological sectors and for both kink-antikink ($K\bar K$) and $\bar K K$ orderings. In the $(-1/2,1/2)$ sector, the kink-antikink pair annihilates for all initial velocities. To the best of our knowledge, this full-velocity annihilation regime has not been reported in $\phi^8$ kink collisions. We also find fractal multi-bounce windows in the $(-1,-1/2)$, $(-1,-1/3)$, and $(-1/3,1/3)$ sectors. Our main result indicates an effective-potential classification of these collision outcomes. We show that the shape of the effective potential is closely related to the final channel. It determines whether the pair escapes, forms a bion, annihilates, or changes sector. When the solitons pass through each other, the effective potential can change suddenly. This gives a possible mechanism for annihilation and sector change. Our results establish connections among topological structure, spectrum and effective potentials in higher-order scalar field theories.

hep-th↗

arXiv2025

A novel reverberation mapping method for blazars

Reverberation mapping (RM) is the most promising method to measure the masses of supermassive black holes in the center of active galaxy nuclei (AGNs). However, the dominant jet component hinders the application of RM method for blazars. In this work, we present a new algorithm to disentangle the contribution of the accretion disk from that of the relativistic jet in blazars by analyzing the spectral break of the optical spectroscopic data. We applied this method to two flat-spectrum radio quasars (FSRQs), PKS 1510-089 and PKS 0736+017. In PKS 1510-089, the variability of the H$\gamma$ line is delayed with respect to the disk emission by approximately 94 days, while the H$\beta$ line shows a lag of about 111 days relative to the disk. In PKS 0736+017, the H$\gamma$ variability is delayed with respect to the disk by roughly 66 days, and the H$\beta$ line exhibits a lag of about 67 days. Based on these measured time lags, we estimate black hole masses of $\sim1.4\times10^{8}\,M_{\odot}$ for PKS 1510-089 and $\sim8.1\times10^{7}\,M_{\odot}$ for PKS 0736+017. This method paves the way to apply the RM method for blazars, and improves the understanding of disk and jet activities.

astro-ph.HE↗

arXiv2025

Unveiling the Cosmic Dance of Repeated Nuclear Transient ASASSN-14ko: Insights from Multiwavelength Observations

ASASSN-14ko is a periodically repeating nuclear transient. We conducted high-cadence, multiwavelength observations of this source, revealing several recurrent early bumps and rebrightenings in its UV/optical light curves. The energy released during these bumps and rebrightenings shows a diminishing trend in recent UV/optical outbursts, which we monitored through multiwavelength observations. These features can be ascribed to the interaction between stream debris and the expanded disk in the repeated partial tidal disruption event. The X-ray light curve exhibits an inverse pattern compared to the UV/optical bands, displaying sporadic outbursts. Furthermore, our observations demonstrate that the blackbody temperature and radius in each outburst increase with the UV/optical luminosity, and such evolution resembles that observed in X-ray quasiperiodic eruptions, whereas distinguishing it from typical tidal disruption events.

astro-ph.HE↗

arXiv2025

Fractal structure of Christ-Lee model

This paper numerically investigates the dynamical properties of kink and antikink collisions in the Christ_Lee model in the regime of epsilon approaching the phi4 theory. With given epsilon and the initial velocity Vin, we exhibiting the formation of bion, scattering, and n_bounce states. Additionally, we show the self_similar fractal structures in the plot of Vout_Vin with given epsilon. Specially, we find the fractal structure in the plot of Vout versus epsilon, which is not reported previously. We computes the Box_counting dimension for these fractal structures. We find that the Box_dimension is positively correlated with epsilon, and approaches to Hausdorff dimension of the Sierpinski triangle when epsilon is sufficiently large.

cond-mat.stat-mech↗

arXiv2025

A sample study on the Fermi-LAT spectral variation behavior of blazars

In this study, we analyze the $\sim 16$ yr Fermi-LAT data of 160 blazars consisting of 92 flat-spectrum radio quasars (FSRQs), 64 BL Lacertae type objects (BL Lacs), and 4 blazar candidates of unknown type objects (BCU), and exhibit their spectral variation. By fitting a linear model ($y = kx + b$) to the monthly binned flux-index plots, we find that most of the FSRQs ($\sim 89\%$) display a harder-when-brighter (HWB) trend ($k>0$), while the majority of BL Lacs ($\sim 64\%$) exhibit a softer-when-brighter (SWB) trend ($k<0$). By plotting their slope ($k$) versus their variability index and inverse Compton (IC) peak frequency, we find a moderate positive correlation between $k$ and the variability index, and we find a moderate negative correlation between $k$ and the IC peak frequency, which we name as the gamma-ray variability sequence of blazars. Additionally, 7 blazars may not follow the linear variation trend, particularly in PKS 0537-441, AP Librae, and PKS 1510-089. Additional very-high-energy gamma-ray emission components may be the cause of the break in the variation trend.

astro-ph.HE↗

arXiv2024

A toy model to explain the missing bounce windows in the kink-antikink collisions

We propose a toy model to reproduce the fractal structure of kink and antikink collisions on one topological sector of $ϕ^6$ theory. Using the toy model, we investigate the missing bounce windows observed in the fractal structure, and show that the coupling between two oscillation modes modulate the emergence of the missing bounce windows. By numerical calculation, we present that the two bounce resonance corresponds to the lower eigenfrequency of the toy model.

hep-th↗

arXiv2024

Solving the Spectral Problem via the Periodic Boundary Approximation in $ϕ^6$ Theory

In $ϕ^6$ theory, the resonance scattering structure is triggered by the so-calls delocalized modes trapped between the $\bar{K}K$ pair. The frequencies and configurations of such modes depend on the $\bar{K}K$ half-separation 2$a$, can be derived from the Schrödinger-like equation. We propose to use the periodic boundary conditions to connect the localized and delocalized modes, and use periodic boundary approximation (PBA) to solve the spectrum analytically. In detail, we derive the explicit form of frequencies, configurations and spectral wall locations of the delocalized modes. We test the analytical prediction with the numerical simulation of the Schrödinger-like equation, and obtain astonishing agreement between them at the long separation regime.

hep-th↗

arXiv2023

A small scale structure model of jet based on the observation of microvariability

We developed a multi-region radiation model for the evolution of flux and spectral index with time. In this model, each perturbation component in the jet produces an independent flare. The model can be used to study the decomposition of microvariability, the structural scale of the perturbed components, and the physical parameters of the acceleration processes. Based on the shock acceleration model in relativistic jet, the influence of acceleration parameters on multiband flare parameters is calculated. We present the results of multiband optical microvariability of the blazar BL Lacertae observed performed during 89 nights in the period from 2009 to 2021, and use them as a sample for model fitting. The results show that both the amplitude and duration of flares decomposed from the microvariability light curves confirm a lognormal distribution. The time delays between the optical bands follow the normal distribution and amount to several minutes, that corroborates with both predictions from the theoretical model and the calculation of the discrete correlation function (DCF). Using the spectral index evolution and the simultaneous fitting of the multiband variability curves, we obtain the acceleration and radiation parameters to constrain and distinguish the origins of different flares. Based on the flare decomposition, we can well reproduce the time-domain evolution trends of the optical variation and energy spectrum, and explain the various redder-when-brighter (RWB) and/or bluer-when-brighter (BWB) behavior.

astro-ph.HE↗

arXiv2022

Exploration of the origin of 2020 X-ray outburst in OJ 287

Research into OJ 287 has been ongoing for many years. In 2020 April-June, this source underwent the second highest X-ray outburst (second only to the 2016-2017 outburst) and the mechanism of this outburst is still under debate. In this paper, we discuss two scenarios to explore the origin of the outburst: an after-effect of a black hole-disc impact and a tidal disruption event (TDE). We present the weak correlations of the spectral index versus X-ray flux and the hardness ratio (HR) versus the soft X-ray flux during the outburst, and these features are different from the case in the quiescent state. The correlations are compared with those of the 2016-2017 outburst with the highest X-ray flux in monitoring history. Analysis of the outbursts in 2016-2017 and 2020 shows that the expected time of the X-ray outburst, based on the theory of the after-effect of the black hole-disc impact and the estimation of available data, is inconsistent with historical observations. The soft X-ray spectra, the barely temporal evolution of colour, and the evolution of the HR mean that the 2020 outburst shares similar features with the 2016-2017 outburst, which was considered as a possible candidate for a TDE. Additionally, we find that the predictions of full TDEs ($t^{-5/3}$) and partial TDEs ($t^{-9/4}$) for the soft X-ray decay light curve are well fitted. Our analysis suggests that the 2020 outburst in OJ 287 is probably related to the TDE candidate.

astro-ph.HE↗

arXiv2021

A possible tidal disruption event candidate in the black hole binary system of OJ 287

The BL Lacertae OJ 287 is a supermassive black holes binary (SMBHB) system with complex physics of its irregular flares. During 2016 October -- 2017 April period, a surprising outburst in the X-ray, UV and optical bands was detected, while no variability was seen in the $γ$-ray light curve. During the outburst, the X-ray light curves were dominated by the soft X-rays, whose peak in the luminosity was $\sim$ $10^{46}\text{erg}~\text{s}^{-1}$ -- more than 10 times higher than the mean level before the outburst -- and a "softer-when-brighter" phenomenon was exhibited. These above phenomena have been reported by some previous works. The hardness ratio showed negligible evolution with flare time and soft X-ray luminosity. Critically, the luminosity of the soft X-rays decayed following a power law of $t^{-5/3}$ which occurs in most tidal disruption events (TDEs), and similar trend can be seen in UV and optical bands during the soft X-ray declining period. Helium and oxygen narrow emission lines are strengthened prominently in the optical spectra of postoutburst epochs, that could be attributed to the surrounding gas appeared due to TDE. We discuss three possible origins of the event, including the jet's precession, the aftereffect of the black hole-disk impaction and the TDE. Our results show that the TDE is the more likely scenario to explain the outburst.

astro-ph.HE↗

arXiv2021

The X-ray outburst of PG 1553+113: A precession effect of two jets in the supermassive black hole binary system

Blazar PG 1553+113 is thought to be a host of supermassive black hole binary (SMBHB) system. A 2.2-year quasi-periodicity in the $γ$-ray light curve was detected, possibly result of jet precession. Motivated by the previous studies based on the $γ$-ray data, we analyzed the X-ray light curve and spectra observed during 2012--2020. The 2.2-year quasi-periodicity might be consistent with the main-flare recurrence in the X-ray light curve. When a weak rebrightening in the $γ$-ray was observed, a corresponding relatively strong brightening in the X-ray light curve can be identified. The "harder-when-brighter" tendency in both X-ray main and weak flares was shown, as well as a weak "softer-when-brighter" behavior for the quiescent state. We explore the possibility that the variability in the X-ray band can be interpreted with two-jet precession scenario. Using the relation between jets and accretion discs, we derive the primary black hole mass $\simeq 3.47\times 10^8M_{\odot}$ and mass of the secondary one $\simeq 1.40\times 10^8M_{\odot}$, and their mass ratio $\sim 0.41$.

astro-ph.HE↗

arXiv2021

Interpreting the variation phenomena of B2 1633+382 via the two-component model

Blazars are variable targets in the sky, whose variation mechanism remains an open question. In this work, we make a comprehensive study on the variation phenomena of the spectral index and polarization degree (PD) to deeply understand the variation mechanism of B2 1633+382 (4C 38.41). We use the local cross-correlation function (LCCF) to perform the correlation analysis between multi-wavelength light curves. We find that both $γ$-ray and optical $V$-band are correlated with the radio 15 GHz at the beyond 3$σ$ confidence level. Based on the lag analysis, the emitting regions of $γ$-ray and optical locate at $14.2_{-2.4}^{+0}$ pc and $14.2_{-8.3}^{+8.3}$ pc upstream of the core region of radio 15 GHz, and are far away from the broad-line region (BLR). The broad lines in the spectrum indicate the existence of the accretion disk component in the radiation. Thus, we consider the two-component (TC) model, which includes the relative constant background component and the varying jet component to study the variation behaviors. The Markov Chain Monte Carlo (MCMC) procedure is adopted to study the physical parameters of the jet and the background components. To some extent, the study of normalized residuals indicates that the TC model fits better than the linear fitting model. The jet with helical magnetic field is hopeful to explain the variation, and the shock in jet model is not completely ruled out.

astro-ph.HE↗

arXiv2020

A comprehensive study on the variation phenomena of AO 0235+164

The variation mechanism of blazars is a long standing open question. The polarization observation can provide us with more information to constrain models. In this work, we collect the long term multi-wavelength data of AO 0235+164, and make correlation analysis between them by using the local cross-correlation function (LCCF). We found that both $γ$-ray and the optical {\it V}-band light curves are correlated with the radio light curve at beyond 3$σ$ significance level. The emitting regions of the $γ$-ray and the optical coincide within errors, and locate at {$6.6_{-1.7}^{+0.6}$} pc upstream of the core region of 15 GHz, which are beyond the broad line region (BLR). The color index shows the redder when brighter (RWB) trend at the low flux state, but turns to the bluer when brighter (BWB) trend at the high flux state. While, the $γ$-ray spectral index always shows the softer when brighter (SWB) trend. We propose that such complex variation trends can be explained by the increasing jet component with two constant components. The {optical} PD flares and {optical} flux flares are not synchronous. It seems that one flux peak are sandwiched by two PD peaks, which have inverse rotation trajectories in the $qu$ plane. The helical jet model can schematically show these characteristics of polarization with fine tuned parameters. The change of viewing angle is suggested to be the primary variable which lead all these variations, although other possibilities like the shock in jet model or the hadronic model are not excluded completely.

astro-ph.HE↗

arXiv2020

Curvature induced polarization and spectral index behavior for PKS 1502+106

A comprehensive study of multifrequency correlations can shed light on the nature of variation for blazars. In this work, we collect the long-term radio, optical and $γ$-ray light curves of PKS 1502+106. After performing the localized cross-correlation function analysis, we find that correlations between radio and $γ$-ray or $V$ band are beyond the $3σ$ significance level. The lag of the $γ$-ray relative to 15 GHz is $-60^{+5}_{-10}$ days, translating to a distance $3.18^{+0.50}_{-0.27}$ parsec (pc) between them. Within uncertainties, the locations of the $γ$-ray and optical emitting regions are roughly the same, and are away from the jet base within $1.2$ pc. The derived magnetic field in optical and $γ$-ray emitting regions is about $0.36$ G. The logarithm of $γ$-ray flux is significantly linearly correlated with that of $V$ band fluxes, which can be explained by the synchrotron self-Compton (SSC) process, the external Compton (EC) processes, or the combination of them. We find a significant linear correlation in the plot of $\log\prod$ (polarization degree) versus $\log νF_ν$ at $V$ band, and use the empirical relation $Π\sim \sin^n θ'$ ($θ'$ is the observing angle in the comoving frame blob) to explain it. The behaviors of color index (generally redder when brighter at the active state) and $γ$-ray spectral index (softer when brighter) could be well explained by the twisted jet model. These findings suggest that the curvature effect (mainly due to the change of the viewing angle) is dominant in the variation phenomena of fluxes, spectral indices, and polarization degrees for PKS 1502+106.

astro-ph.HE↗

arXiv2019

Statistical analysis of micro-variability properties of the blazar S5 0716+714

The typical blazar S5 0716$+$714 is very interesting due to its rapid and large amplitude variability and high duty cycle of micro-variability in optical band. We analyze the observations in I, R and V bands obtained with the $1.0m$ telescope at Weihai observatory of Shandong University from 2011 to 2018. The model of synchrotron radiation from turbulent cells in a jet has been proposed as a mechanism for explaining micro-variability seen in blazar light curves. Parameters such as the sizes of turbulent cells, the enhanced particle densities, and the location of the turbulent cells in the jet can be studied using this model. The model predicts a time lag between variations as observed in different frequency bands. Automatic model fitting method for micro-variability is developed, and the fitting results of our multi-frequency micro-variability observations support the model. The results show that both the amplitude and duration of flares decomposed from the micro-variability light curves confirm to the log-normal distribution. The turbulent cell size is within the range of about 5 to 55 AU, and the time lags of the micro-variability flares between the I-R and R-V bands should be several minutes. The time lags obtained from the turbulence model are consistent with the fitting statistical results, and the time lags of flares are correlated with the time lags of the whole light curve.

astro-ph.HE↗

arXiv2017

Near integrability of kink lattice with higher order interactions

In the paper, we make use of Manton's analytical method to investigate the force between kink and the anti-kink with large distance in $1+1$ dimensional field theory. The related potential has infinite order corrections of exponential pattern, and coefficients for each order are determined. These coefficients can also be obtained by solving the equation of the fluctuation around the vacuum. At the lowest order, the kink lattice represents the Toda lattice. With higher order correction terms, the kink lattice can represent one kind of the generic Toda lattice. With only two sites, the kink lattice is classically integrable. If the number of sites of the lattice is larger than two, the kink lattice is not integrable but a near integrable system. We take use of the Flaschka's variables to study the Lax pair of the kink lattice. These Flaschka's variables have interesting algebraic relations and the non-integrability can be manifested. We also discussed the higher Hamiltonians for the deformed open Toda lattice, which has a similar result as the ordinary deformed Toda.

math-ph↗

arXiv2016

Toda chain from the kink-antikink lattice

In this paper, we have studied the kink and antikink solutions in several neutral scalar models in 1+1 dimension. We follow the standard approach to write down the leading order and the second order force between long distance separated kink and antikink. The leading order force is proportional to exponential decay with respect to the distance between the two nearest kinks or antikinks. The second order force have a similar behavior with the larger decay factor, namely $3\over 2$. We make use of these properties to construct the kink lattice. The dynamics of the kink lattice with leading order force can be identified as ordinary nonperiodic Toda lattice. Also the periodic Toda lattice can be obtained when the number of kink lattice is even. The system of kink lattice with force up to the next order corresponds to a new specific deformation of Toda lattice system. There is no well study on this deformation in the integrable literatures.We found that the deformed Toda system are near integrable system, since the integrability are hindered by high order correction terms. Our work provides a effective theory for kink interactions and a new near or quasi integrable model.

hep-th↗

arXiv2015

The Broad Band Spectral Energy Distributions of SDSS Blazars

We compiled the radio, optical, and X-ray data of blazars from the Sloan Digital Sky Survey (SDSS) database, and presented the distribution of luminosities and broad band spectral indices. The distribution of luminosities shows that the averaged luminosity of flat-spectral radio quasars (FSRQs) is larger than that of BL Lacs objects. On the other hand, the broad band spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects (LBLs) objects have similar spectral properties, but high energy peaked BL Lac objects (HBLs) have a distinct spectral property. This may be due to that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme also is revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameter.

astro-ph.HE↗