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Correlations between γ-ray luminosity and magnetization of the jet as well as relativistic electron injection power:cases for Mrk 421, 3C 454.3 and 3C 279

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arXiv 2021年

作者： Hu, Wen Yan, Da-Hai Hu, Qiang-Lin Department of Physics Jinggangshan University Ji’anJiangxi Province343009 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories Chinese Academy of Sciences Kunming650011 China

By fitting high-quality and simultaneous multi-wavelength (MWL) spectral energy distributions (SEDs) at multiple epochs with a one-zone leptonic jet model, we study jet properties of the three famous blazars Mrk 421, 3C 454.3 and 3C 279. In the jet model, the emitting electron energy distributions (EEDs) are calculated by solving the kinetic equation of electron injection, escape, adiabatic and radiative energy losses. To explore multi-dimensional parameter space systematically, we employ a Markov chain Monte Carlo (MCMC) fitting technique. The properties of emission regions we derived here are consistent with those in previous studies, e.g., the particle-dominated and low-magnetization jet. The new finding is that there is a tight correlation between γ-ray luminosity and electron injection power and an anti-correlation between γ-ray luminosity and jet magnetization parameter. The results suggest that same energy-dissipative mechanism (like a shock) could be operating in the jets of different types of blazars, and the origin of γ-ray flares is associated with the particle acceleration process. Copyright © 2021, The Authors. All rights reserved.

关键词： Energy dissipation

One Fits All: A Unified Synchrotron Model Explains GRBs with FRED-Shaped Pulses

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arXiv 2023年

作者： Yan, Zhen-Yu Yang, Jun Zhao, Xiao-Hong Meng, Yan-Zhi Zhang, Bin-Bin School of Astronomy and Space Science Nanjing University Nanjing210093 China Key Laboratory of Modern Astronomy and Astrophysics Nanjing University Ministry of Education China Yunnan Observatories Chinese Academy of Sciences Kunming China Center for Astronomical Mega-Science Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China Purple Mountain Observatory Chinese Academy of Sciences Nanjing210023 China

The analysis of gamma-ray burst (GRB) spectra often relies on empirical models lacking a distinct physical explanation. Previous attempts to couple physical models with observed data focus on individual burst studies, fitting models to segmented spectra with independent physical parameters. However, these approaches typically neglect to explain the time evolution of observed spectra. In this study, we propose a novel approach by incorporating the synchrotron radiation model to provide a self-consistent explanation for a selection of single-pulse GRBs. Our study comprehensively tests the synchrotron model under a unified physical condition, such as a single injection event of electrons. By tracing the evolution of cooling electrons in a decaying magnetic field, our model predicts time-dependent observed spectra that align well with the data. Using a single set of physical parameters, our model successfully fits all time-resolved spectra within each burst. Our model suggests that the rising phase of the GRB light curve results from the increasing number of radiating electrons, while the declining phase is attributed to the curvature effect, electron cooling, and the decaying magnetic field. Our model provides a straightforward interpretation of the peak energy's evolution, linked to the decline of the magnetic field and electron cooling due to the expansion of the GRB emission region. Our findings strongly support the notion that spectral and temporal evolution in GRB pulses originates from the expansion of the GRB emission region, with an initial radius of approximately 1015 cm, and synchrotron radiation as the underlying emission mechanism. Copyright © 2023, The Authors. All rights reserved.

关键词： Synchrotron radiation

A quasi-periodic oscillation in the γ-ray emission from the non-blazar active galactic nucleus PKS 0521-36

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arXiv 2021年

作者： Zhang, Haiyun Yan, Dahai Zhang, Pengfei Yang, Shenbang Zhang, Li Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatory Chinese Academy of Sciences Kunming650011 China

Long-term γ-ray variability of a non-blazar Active Galactic Nucleus (AGN) PKS 0521-36 is investigated by using Fermi-LAT pass 8 data covering from 2008 August to 2021 March. The results show that the histogram of the γ-ray fluxes follows a log-normal distribution. Interestingly, in the analysis of ∼5.8-year (from MJD 56317 to 58447) LAT data between two outbursts (occurring during 2012 October and 2019 May respectively), a quasi-periodic oscillation (QPO) with a period of ∼ 1.1 years (∼ 5σ of significance) is found in the Lomb-Scargle Periodogram (LSP), the Weighted Wavelet Z-transform (WWZ) and the REDFIT results. This quasi-periodic signal also appears in the results of Gaussian process modeling the light curve. Therefore, the robustness of the QPO is examined by four different methods. This is the first γ-ray QPO found in a mildly beamed jet. Our results imply that the γ-ray outbursts play an important role in the formation of the γ-ray QPO. © 2021, CC BY.

关键词： Gamma rays

Mean-squared displacement and variance for confined Brownian motion

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arXiv 2023年

作者： Liao, Yi Hao, Yu-Zhou Gong, Xiao-Bo Department of Materials Science and Engineering College of Engineering Southern University of Science and Technology Shenzhen518055 China Department of Physics College of Science Southern University of Science and Technology Shenzhen518055 China State Key Laboratory for Mechanical Behavior of Materials School of Materials Science and Engineering Xi’an Jiaotong University Xi’an710049 China Yunnan Observatory Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China

For one-dimension Brownian motion in the confined system with the size L, the mean-squared displacement(MSD) defined by 〈(x − x0)2〉 should be proportional to tα(t). The power α(t) should range from 1 to 0 over time, and the MSD turns from 2Dt to cL2, here the coefficient c independent of t, D being the diffusion coefficient. The paper aims to quantitatively solve the MSD in the intermediate confinement regime. The key to this problem is how to deal with the propagator and the normalization factor of the Fokker-Planck equation(FPE) with the Dirichlet Boundaries. Applying the Euler-Maclaurin approximation(EMA) and integration by parts for the small t, we obtain the MSD being (Formular presented), with (Formular presented), t and the power α(t) being 1-0.18√ξ /1-0.18√ξ. Further, we analysis the MSD and the power for the d-dimension system with γ-dimension confinement. In the case of γ 2〉. In the finite system, the variance is not necessarily the same as MSD. The initial conditions are essential to characterize the diffusion behavior described by the FPE, especially in the finite system. Under the initial condition referring to the different probability density function(PDF) being p0(x), MSD and PV should exhibit different dependencies on time, which reflect corresponding diffusion *** examples, the paper discusses the representative initial PDFs reading p0(x) = δ(x − x0), with the midpoint x0 = L/2 and the endpoint x0 = ∊(or 0+). In the case of midpoint, the MSD(equal to PV) reads 2Dt(1 − 5π3Dt)/L2 for the small t, which reflects a kind of sub-diffusion, with D being the diffusion coefficient. In the case of endpoint, the MSD(equal to PV) reads 4/π (2Dt)[1 + 2√πDt/L ] for the small t, which reflects a kind of super-diffusion. © 2023, CC BY.

关键词： Diffusion

ASAS J174406+2446.8 is identified as a marginal-contact binary with a possible cool third body

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Research in Astronomy and Astrophysics 2020年第6期20卷 265-272页

作者： Xiang-Dong Shi Sheng-Bang Qian Lin-Jia Li Wei-Wei Na Xiao Zhou Yunnan Observatories Chinese Academy of SciencesKunming 650216China University of Chinese Academy of Sciences Beijing 100049China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China Yuxi Normal University Yuxi 653100China

ASAS J174406+2446.8 was originally found as aδScuti-type pulsating star with the period P=0.189068 d by ASAS ***,the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the log g-T diagram ofδScuti pulsating *** understand the physical properties of the variable star,we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan ***-color light curves in B,V,R_c and I_c bands were obtained and are analyzed by using the W-D *** is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781 d rather than aδScuti *** is a W-subtype contact binary with a mass ratio of 1.135(±0.019)and a fill-out factor of 10.4%(±5.6)%.The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn,ⅡPer and GW *** of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation *** linear ephemeris was corrected by using 303 new determined times of light *** is detected that the O-C curve shows a sinusoidal variation that could be explained by the light-travel-time effect via the presence of a cool red *** present investigation reveals that some of theδScuti-type stars beyond the red edge of pulsating instability strip on the log g-T diagram are misclassified eclipsing *** understand their structures and evolutionary states,more studies are required in the future.

关键词： stars binaries close-stars binaries eclipsing-stars δScuti-stars individual(ASAS J174406+2446.8)

On the narrow spectral feature at ∼3 TeV in the MAGIC spectrum of Mrk 501

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arXiv 2021年

作者： Hu, Wen Yan, Dahai Department of Physics Jinggangshan University Jiangxi Province Ji'an343009 China Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Observatories Chinese Academy of Sciences Kunming650011 China

Using a time-dependent one-zone leptonic model that incorporates both shock acceleration and stochastic acceleration processes, we investigate the formation of the narrow spectral feature at ∼ 3 TeV of Mrk 501 which was observed during the X-ray and TeV flaring activity in July 2014. It is found that the broadband spectral energy distribution (SED) can be well interpreted as the synchrotron and synchrotron-self-Compton emission from the electron energy distribution (EED) that is composed by a power-law (PL) branch and a pileup branch. The PL branch produces synchrotron photons which are scattered by the electrons of the pileup branch via inverse-Compton scattering and form the narrow spectral feature observed at the TeV energies. The EED is produced by two injection episodes, and the pileup branch in EED is caused by shock acceleration rather than stochastic acceleration. Copyright © 2021, The Authors. All rights reserved.

关键词： Stochastic systems

Four Changing-Look Active Galactic Nuclei Found From Optical Variations

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arXiv 2024年

作者： Zhu, Li-Tao Li, Jie Wang, Zhongxiang Zhang, Ju-Jia Department of Astronomy School of Physics and Astronomy Yunnan University Kunming650091 China Laboratory for Research in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China Hefei230036 China School of Astronomy and Space Science University of Science and Technology of China Hefei230026 China Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai200030 China Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China

We report the finding of four changing-look (CL) active galactic nuclei (AGN). We selected these sources due to their potential as interesting targets when considering their relatively-large optical flux variations and related mid-infrared flux variations. To identify their CL feature, we use archival spectra from the Sloan Digital Sky Survey (SDSS) taken at least 8 years ago as well as spectra taken recently from the Transient Name Server (TNS) and with the 2.4-m LiJiang telescope (LJT). We study the sources' spectral changes by fitting and determining the H_ and H_ components and verify their CL behavior. When comparing the TNS and/or LJT spectra to the SDSS ones, all four sources showed the appearance of a broad or a stronger broad H_ component and a relatively weak broad H_ component. As two of the four sources are established to have a brighter-and-bluer feature in the photometric data, during the time periods in which the TNS and LJT spectra were taken, this feature likely accompanied the turn-on of the broad components. Thus, we suggest that this brighter-and-bluer feature can be used as a criterion for efficiently finding CL sources among previously spectroscopically classified type 2 AGN, such as from among the sources provided by the SDSS. Copyright © 2024, The Authors. All rights reserved.

关键词： Active Galactic Nuclei

The carbon-to-H2, CO-to-H2 conversion factors and carbon abundance on kiloparsec scales in nearby galaxies

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arXiv 2021年

作者： Jiao, Qian Gao, Yu Zhao, Yinghe Nanjing210023 China Department of Astronomy Xiamen University XiamenFujian361005 China Yunnan Observatories & Key Laboratory for the Structure and Evolution of Celestial Objects CAS Kunming650011 China

Using the atomic carbon [C i] (3P1 → 3P0) and [C i] (3P2 → 3P1) emission (hereafter [C i] (1−0) and [C i] (2−1), respectively) maps observed with the Herschel Space Observatory, and CO (1−0), Hi, infrared and submm maps from literatures, we estimate the [C i]-to-H2 and CO-to-H2 conversion factors of α[CI] (1−0), α[CI] (2−1), and αCO at a linear resolution ∼ 1 kpc scale for six nearby galaxies of M 51, M 83, NGC 3627, NGC 4736, NGC 5055, and NGC 6946. This is perhaps the first effort, to our knowledge, in calibrating both [C i]-to-H2 conversion factors across the spiral disks at spatially resolved ∼ 1 kpc scale though such studies have been discussed globally in galaxies near and far. In order to derive the conversion factors and achieve these calibrations, we adopt three different dust-to-gas ratio (DGR) assumptions which scale approximately with metallicity taken from precursory results. We find that for all DGR assumptions, the α[CI] (1−0), α[CI] (2−1), and αCO are mostly flat with galactocentric radii, whereas both α[CI] (2−1) and αCO show decrease in the inner regions of galaxies. And the central αCO and α[CI] (2−1) values are on average ∼ 2.2 and 1.8 times lower than its galaxy averages. The obtained carbon abundances from different DGR assumptions show flat profiles with galactocentric radii, and the average carbon abundance of the galaxies is comparable to the usually adopted value of 3 × 10−5. We find that both metallicity and infrared luminosity correlate moderately with the αCO whereas only weakly with either the α[CI] (1−0) or carbon abundance, and not at all with the α[CI] (2−1). © 2021, CC BY.

关键词： Galaxies

Nine New Cataclysmic Variable Stars with Negative Superhumps

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arXiv 2023年

作者： Sun, Qi-Bin Qian, Sheng-Bang Zhu, Li-Ying Liao, Wen-Ping Zhao, Er-Gang Li, Fu-Xing Shi, Xiang-Dong Li, Min-Yu Yunnan Observatories Chinese Academy of Sciences Kunming650216 China Department of Astronomy Key Laboratory of Astroparticle Physics of Yunnan Province Yunnan University Kunming650091 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Yuquan Road Shijingshan District Beijing China

Negative superhumps (NSHs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. Based on TESS photometry, we find nine new cataclysmic variable stars (CVs) with NSHs. Three (ASAS J1420, TZ Per, and V392 Hya) of these stars similar to AH Her still have NSHs during dwarf nova outbursts, and the NSH amplitude varies with the outburst. The variation in the radius of the accretion disk partially explains this phenomenon. However, it does not explain the rebound of the NSH amplitude after the peak of the outburst and the fact that the NSH amplitude of the quiescence is sometimes not the largest, and it is necessary to combine the disk instability model (DIM) and add other ingredients. Therefore, we suggest that the variation of NSH amplitude with outburst can be an essential basis for studying the origin of NSHs and improving the DIM. The six (ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF18acakuxo) remaining stars have been poorly studied, and for the first time we determine their orbital periods, NSHs and Superorbital signal (SOR) periods. The NSH periods and amplitudes of ASASSN-V J1137 and ASASSN-17qj vary with the SOR, and based on the comparison of the observations with the theory, we suggest that a single change in tilted disk angle does not explain the observations of the SOR and that other ingredients need to be considered as well. Copyright © 2023, The Authors. All rights reserved.

关键词： Stars