Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： Multi band correlation analysis is of great significance to the study of the physical model and radiation mechanism of Blazars. In order to study the physical model of TeV Blazars, we search and sort out their γ-ray band data and optical band data according to the names and coordinates of their counterparts of 78 TeV Blazars in the 4FGL-DR3 catalogue, and find that there are 56 TeV Blazars with both optical band and γ-ray band data. The Discrete Correlation Function (DCF) is used to calculate the correlation between the optics and γ-ray of each Blazar. The calculation results show that 20 sources show weak γ-ray-optical correlation, 30 sources show strong γ-ray-optical correlation, and 6 sources show no γ-ray-optical correlation. Among sources that exhibit strong correlation. there is also varying degrees of time delay between the optical and γ-ray bands. These results support that the high-energy photons of TeV Blazar mainly come from synchronous self Compton radiation of lepton model. However, we also find that there are some “orphan flares” in both the optical and γ-ray bands, which may indicate that the source of low energy photons is not unique.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： We study the characteristics of radio galaxy (RDG) and Narrow line Seyfert 1 (NLSY1) in the fourth Fermi LAT catalogue, the distribution characteristics of γ-ray flux and the RMS-Flux linear relationship. Based on these two types of active galactic nuclei in the data processing of γ-ray flux, the Gaussian function and log-normal distribution function are used to fit the flux distribution. By K-S test, S-W test, and reduced chi square χ2. It is found that the distributions of RDG and NLSY1 are more consistent with the log-normal distribution than the Gaussian distribution, which indicates that their light variability may have nonlinear and multiplicative properties. In addition, linear fitting is also performed on two different groups of RMS-Flux for these two types of sources, and it is found that RMS-Flux has a strong linear correlation and its slopes are both positive.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： The 1 m New Vacuum Solar Telescope (NVST) is capable of high-resolution imaging observations better than 0.2″, but cannot yet routinely observe high-resolution magnetic fields. Many magnetic structures and solar activity exist at small scales, requiring high-resolution magnetic field observations. NVST offers excellent seeing, and if the magnetometer has fast modulation capabilities and is coupled with statistical reconstruction techniques, it is expected to achieve high-resolution solar magnetic field measurements. The main problems faced by NVST in measuring magnetic fields include time-varying polarisation due to bending-axis optical paths, optical axis shifts due to telescope attitude changes and wind loading, and the effects of turbulence. In this paper, we analyze in detail the requirements for high-resolution observation of the solar magnetic field and the solar magnetic field measurement problems faced by NVST, formulate the basic parameters of the magnetometer, propose the requirements for the polarisation analyzer, and design a high-resolution observation scheme for the photospheric magnetic field. Finally, the optical path for the magnetometer is designed using ZEMAX optical design software, and the results show that the optical design can meet the requirements of high-resolution imaging.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： The classification of gamma-ray bursts (GRBs) is an unsolved hot issue in the field of GRBs. To solve this problem, we collected a samples of X-ray afterglow curves including 180 known redshift GRBs observed by Swift with slow attenuation and subsequent attenuation characteristics, in which there are 172 Long GRBs and 8 Short GRBs. We adopt the smooth broken power law function and the Markov chain Monte Carlo (MCMC) method to fit these X-ray afterglow light curves. After obtaining these light curve characteristic parameters α1 (slow decay index), α2 (normal attenuation index), and Ta (slow attenuation end time in rest frame), we analyze the characteristic parameters of the two types of bursts to check whether there are differences in the distribution of these parameters and whether the two types of storms follow the same correlation. Our research findings are as follows: (1) The distribution range, median value, and average value of the characteristic parameters (α1､α2, Ta) of two types of bursts are very close, and there is no significant difference. The subsequent K-S test further indicates that there is no significant difference in the distribution of parameters between the two types of bursts. (2) The two types of bursts we selected follow the following correlation: Lx –Ta, Lx –Eγ,iso､S-T90､Eγ,iso -T90, and they are not distinguishable on a scatter chart. These statistical results indicate that the optical variability characteristics of the two types of bursts are similar. Therefore, we infer that the two types of GRBs have the same physical origin, and their jet structures may also be the same.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： Based on the long-term monitoring data at 1 mm wavelength from the Submillimeter Array(SMA), we used a Bayesian hierarchical model to fit the light curves of 155 blazars and estimated their radio brightness temperatures and variability Doppler factors. The brightness temperature and Doppler factor distributions between BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs), as well as between Fermi and non-Fermi blazars, were compared using the Wilcoxon rank-sum test. The results show that (1) FSRQs have higher average Doppler factor than BL Lacs; (2) Fermi blazars have higher average brightness temperature and Doppler factor than non-Fermi blazars. After comparing the brightness temperatures and variability Doppler factors at 1 mm and 15 GHz wavelengths, we found a tendency of decreasing towards higher frequencies for these two parameters.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-20 Cooperative journals: 《天文研究与技术》
Abstract： The variability is an important observational feature of Blazars. In order to study the multiband optical variability of Blazar, we collected the light curves of PKS 1424-41 of the gamma-ray band (0.1-100GeV), optical R band, near infrared K band, X band and radio band, released by Fermi LAT, SMARTS, SWIFT (XRT) and Submillimeter Array (SMA). Discrete correlation function is used to analyze the correlation between the light curves. The results show that the gamma-ray band, X-band, optical R-band, near-infrared K-band and radio band are strongly correlated with each other, and there is a time delay between the bands. This result supports the “single region” lepton radiation model. The LSP (Lomb-Scargle Periodogram) method is used to analyze the Quasi-periodic Oscillations (QPO) of PKS 1424-41 for the γ band Light Curve in a flare period (MJD56100-MJD56500). It is found that there are two QPOs in this period: ~75 days and ~50 days, with a ratio of 3∶2. The helical structure of the jet itself and the radiation of high-energy plasma matter moving within it may be the origin of this monthly QPO.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-13 Cooperative journals: 《天文研究与技术》
Abstract： There are two obvious peaks in the spectral energy distribution (SED) of the blazar, of which the low energy peak is the synchrotron radiation peak. There is an inverse correlation between the peak power of the synchrotron radiation peak of the blazar and the peak frequency, so the spectral index plane constructed by the multi-band composite spectral index related to the SED peak can be used as a classifier for the two subclasses of the blazar (flat-spectrum radio quasar (FSRQ) and BL-Lac object). In this paper, the cross matching of multi-wavelength data for the blazars in the Fermi four Catalogue (4FGL-DR3) is carried out through the database of Strasbourg Observatory, and multi-wavelength data set is obtained. Basing on this data set, we find that the distributions of the 8 broad band spectral indices, (αrw1 、αrw2 、αrw3 、αro 、αrγ 、αw1w2 、αw1w3 ）and αw3x , have obvious bimodal structure, and clearly distinguish the two subclasses of blazed variants (FSRQ and BL Lac). Through the support vector machine model in machine learning technology, we further analyze the classification effect of spectral index plane on subclasses of blazar, and find that most of the accuracy rates are above 80%.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-08-30 Cooperative journals: 《天文研究与技术》
Abstract： The spectral energy distributions (SEDs) datas of Mrk421 are collected by our, a total of 73 states as research samples, and the single-region lepton model under the electron energy spectrum of the steady-state transition power law spectrum is applied. Then study the physical properties of Mrk421 jets during the light transition. Our main results are as follows: (1) there is an anticorrelation between magnetic B and Doppler δ in the sample, indicating that magnetic B and Doppler δ are interdependent in the Thomson region.(2) Electron spectral index p1 supports the interpretation of shock wave or magnetic reconnection during light variation of Mrk421.(3) There is a positive correlation between the synchronous peak frequency logνsynpk and the peak luminosity logνsynpkLsynpk, which means that there is an anti-flare variant sequence in the Mrk421 during the light change.(4) According to the equal partition parameter ε=UeUB (the ratio of relativistic electron energy density to magnetic field energy density), the electron energy and magnetic field energy of 26% of the states are nearly equal partition, The electron energy of 63% of the states is an order of magnitude larger than the magnetic field energy, The electron energy of 11% of the states is much larger than the magnetic field energy. This indicates that Mrk 421 is more likely to have the phenomenon that the electron energy is one order of magnitude larger than the magnetic field energy during the light change. It also means that the jets in the Mrk421 are dominated by particles; The relationship from Pe>PB, it is further shown that the Mrk421 jets are particle-dominated, PB≲Pr, meaning that the Poynting flux cannot account for the radiated power, The ranges of Pr/Pe from 0.01 to 0.51, shows that a small fraction of the relativistic electron energy may be used for the observed radiation. (5) Some ranges of the physical parameters of 3C 279 and Mrk421 may be relatively similar, but the physical processes inside the jets of these two sources may not be the same.
Subjects: Astronomy >> Astrophysical processes submitted time 2021-06-18 Cooperative journals: 《天文研究与技术》
Abstract：我们利用Lomb-Scargle periodogram方法和加权小波Z变换(Weight Wavelet Z-transform)方法分析了耀变体CGRaBS J0929+5013和 J2146-1525在15 GHz射电和伽马波段约12年的观测数据。分析结果表明耀变体CGRaBS J0929+5013和J2146-1525在射电波段可能存在准周期振荡信号。它们的准周期分别为1435天(3.93年)和1321天(3.62年)，且置信度均>3(99.7%)；而在伽马波段光变周期性较弱。基于超大质量双黑洞系统中的螺旋喷流模型估算了耀变体CGRaBS J0929+5013和J2146-1525的主黑洞质量的分别为4.3×109和2.7×109。为了探讨射电和伽马波段的光变起源，我们用离散相关函数分别计算了耀变体CGRaBS J0929+5013和J2146-1525射电与伽马波段之间的相关性，发现它们之间没有明显的相关性。这表明它们的辐射可能来自不同的区域。
Subjects: Astronomy >> Astrophysical processes submitted time 2020-11-19 Cooperative journals: 《天文研究与技术》
Abstract：太阳高能活动爆发与活动区内的电流结构有着密切的联系，安培（Ampere）定律j_z=〖1/μ_0 (∇×B)〗_z是测量活动区内视向电流密度的理论基础。由于实测的矢量磁场中不可避免地存在随机噪声，因此，应用安培定律的不同形式计算的电流密度存在显著的差异。为了比较不同形式计算结果的差异并从中探索一种实用的电流计算方法，基于太阳动力学天文台(Solar Dynamic Observatory,SDO)/HMI(Helioseismic and Magnetic Imager)在2011年2月15日测量的活动区AR11158的矢量磁图，运用安培定律的微分算法和积分算法分别计算了活动区内视向电流密度的分布图。结果显示，微分算法获得的视向电流密度j_z分布图受随机噪声的影响要远比积分算法获得的结果大，电流分布图中的电流结构没有积分算法获得的结果清晰。另外，在扩大积分环路半径的情况下，所计算的电流分布图里的噪声信号快速降低，从而使计算的视向电流分布图中的电流结构更清晰。但是当继续扩大积分环路半径时，在获得清晰电流分布图的同时，电流分布图的部分精细结构也随之失真。该研究结果论证了适当扩大积分环路计算视向电流分布图可以降低计算结果受随机噪声的影响，从而获得清晰真实的视向电流分布图，但是积分路径的半径过大在消除噪声影响的同时会丢失电流分布中的一些精细结构。因此在实际计算电流的过程中，应该利用高分辨率的矢量磁图，选定合适的积分路径运用安培定律的积分算法来计算活动区的视向电流，从而帮助我们探索耀斑爆发与活动区内电流结构的关系。
Subjects: Astronomy >> Astrophysical processes submitted time 2020-07-28 Cooperative journals: 《天文研究与技术》
Abstract：一些窄线赛弗特1型星系被发现具有GeV伽马射线辐射(伽马噪)而受到持续关注。 截至目前, 文献共报道22个伽马噪窄线赛弗特1型星系, 另有3个高置信度候选体。利用广域红外巡天探测器(Wide-field Infrared Survey Explorer，WISE)数据平台，获取了这些源W1(3.4 μm)和W2(4.6 μm)两个红外波段的同时性测光数据(2010年1月至2019年12月)。采用参数V和标准额外方差 方法，分析了它们的长期光变现象。结果表明24个源表现出长期亮度(W1星等)变化，17个源表现出长期颜色(W1-W2)变化。通过研究颜色与星等的相关性，发现7个源表现出变亮变红现象(redder-when-brighter, RWB), 4个源表现出变亮变蓝现象(bluer-when-brighter,BWB)。最后简要讨论了颜色变化的可能解释和暗示。
Subjects: Astronomy >> Astrophysical processes submitted time 2020-07-21 Cooperative journals: 《天文研究与技术》
Abstract：耀变体的亮温度与其黑洞喷流能量和吸积率有重要联系。本文搜集和计算了53个耀变体源样本，包括22个BL Lac天体和31个平谱射电类星体(FSRQs)。研究了该样本耀变体亮温度与黑洞喷流能量的分布，并对其子类中亮温度与黑洞喷流能量的相关性进行了讨论。研究结果表明：（1）BL Lac与FSRQs的亮温度与黑洞喷流能量的分布存在明显差异，这可能与BL Lac与FSRQs的内禀性质的区别有关，也可能与其有无发射线及发射线的强弱有关；（2）BL Lac天体的亮温度与黑洞喷流能量之间的相关性较强，亮温度可以在一定程度上描述BL Lac天体的黑洞喷流能量，亮温度大的BL Lac天体的喷流所携带的能量也较大;（3）FSRQs的亮温度与黑洞喷流能量之间有弱相关性，FSRQs的亮温度不能清楚的描述黑洞喷流能量，其黑洞喷流能量受亮温度影响较小。FSRQs的黑洞喷流能量可能受到其他因素的影响。（4）耀变体的亮温度与黑洞吸积率之间有弱的相关性.
Subjects: Astronomy >> Astrophysical processes submitted time 2020-05-06 Cooperative journals: 《天文研究与技术》
Abstract： 本文利用调整流量基准面的方法修正19个费米Blazars的光学波段流量与色指数，通过对比修正前后色指数与星等相关关系，研究多普勒因子对于色指数变化机制的影响。研究表明：（1）修正前，只有5个源呈现明显的BWB趋势，2个源呈现明显的RWB趋势；（2）经过修正后，有9个源呈现明显的BWB趋势，6个源呈现弱的BWB趋势，只有4个源的色指数与星等不存在相关关系；（3）大约有一半的源的色变机制受到多普勒聚束效应的影响，在修正后，这些源的色指数与星等的相关性增强；（4）多普勒因子的变化可能是造成BWB趋势变弱的原因。通过研究色指数和星等的相关关系，能进一步解释Blazars的辐射机制。
Subjects: Astronomy >> Astrophysical processes submitted time 2019-12-02 Cooperative journals: 《天文研究与技术》
Abstract：欧文斯谷射电天文台(OVRO)的长时间监测数据显示平谱射电类星体B3 0307+380的15 GHz射电光变曲线中表现出多个爆发过程. 基于双指数函数，拟合了12个爆发过程，得到了每个爆发过程的光变幅度和上升、下降时标，进而估算了亮温度 和光变多普勒因子 . 多普勒因子范围为 ，平均值 为 . 这个结果表明此源的射电辐射存在明显的聚束效应，支持主流的相对论性喷流模型. 利用Lomb-Scargle周期图(LSP)方法和加权小波分析(WWZ)方法， 探讨了B3 0307+380是否存在周期性光变, 发现存在一个较高置信度（ ）的约244天的周期，并简要讨论了周期可能的存在原因.
Subjects: Astronomy >> Astrophysical processes submitted time 2019-05-13 Cooperative journals: 《天文研究与技术》
Abstract： 基于Swift/BAT所观测的活动星系核(AGN)在硬X射线波段光变曲线数据，通过离散傅利叶变换法,分析了塞弗特1（Seyfert 1）、塞弗特2（Seyfert 2）、平谱射电类星体（FSRQ）、 BL Lac天体功率谱的幂律指数（α）的分布特征。发现Seyfert 2与 I型 AGN 的α 分布有显著差异,而I型AGN 各子类之间的α 分布差异性不显著。Seyfert 2 的硬X射线可能来源于吸积盘内区及热冕，而Seyfert 1 的硬X射线主要来自有外流的冕。我们发现来自相对论性喷流或者外流冕的硬X射线在统计上有更大的幂律指数，而来自吸积盘热冕的硬X射线幂律指数较小。
Subjects: Astronomy >> Astrophysical processes submitted time 2019-04-26 Cooperative journals: 《天文研究与技术》
Abstract： 通过收集数据，用标准吸积盘方法，短时标光变法，连续波混响滞后法，微引力透镜法分析了活动星系核吸积盘辐射区半径，并对四种方法进行分析讨论。结果表明:（1）将耀变体和类星体参数比较，发现两子类的中心黑洞质量、光度和吸积盘辐射区半径都没有明显差别。本文选择了高光度源进行研究，因此出现了两子类以上参数无明显区别的情况；（2）短时标光变法得到的吸积盘辐射区半径比和黑洞质量没有明显的相关性；（3）连续波混响滞后法得到的吸积盘辐射区半径比对黑洞质量的依赖性高于标准α盘模型法，对于无法确定中心黑洞质量的源，可以利用连续波混响滞后法得到吸积盘辐射区半径；（4）微引力透镜法得到的吸积盘辐射区半径比和黑洞质量没有明显的相关性，且该方法只适用于存在微引力透镜效应的类星体，（5）这些方法从观测上证明了吸积盘辐射区半径与黑洞质量存在相关性，验证了标准模型成立。为进一步在观测上寻找这四种方法所需要的源提供了理论上的指导。对活动星系核的吸积盘辐射区半径研究有重要意义。
Subjects: Astronomy >> Astrophysical processes submitted time 2018-05-21 Cooperative journals: 《天文研究与技术》
Abstract： 在收集大量数据的基础上，用时间补偿离散傅里叶变换、Jurkevich方法和离散相关分析法分析了PKS 0735+178的B波段和V波段光变周期，发现该天体具有（4.330.41） 年的光变周期，其中心黑洞质量的下限为0.22106Mʘ。
Subjects: Astronomy >> Astrophysical processes submitted time 2017-09-26 Cooperative journals: 《天文研究与技术》
Abstract：在收集大量数据的基础上，用时间补偿离散傅里叶变换、Jurkevich方法和离散相关分析法分析了PKS 0735+178的B波段和V波段光变周期，发现该天体具有年的光变周期，其中心黑洞质量的下限为。
Subjects: Astronomy >> Astrophysical processes submitted time 2017-09-26 Cooperative journals: 《天文研究与技术》
Abstract：收集了126个BL Lac天体在高能段和甚高能段的观测谱指数，利用数学模型分析其能谱拐折（甚高能与高能观测谱指数之差）。目的是确定河外星系背景光（EBL）吸收是否是导致大红移BL Lac天体能谱拐折的主要原因。统计分析结果为，。统计结果表明，BL Lac天体能谱拐折不仅起源于河外星系背景光吸收，还与其它物理过程有关。
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