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 2023-11-27 Cooperative journals: 《天文研究与技术》
Abstract: We find that the optical band light curve of the blazar PKS 0422 + 004 observed by the Transiting Exoplanet Survey Satellite (TESS) has a quasiperiodic oscillation (QPO) of about 7.4 days in sector 32. We use the Lomb-Scargle Periodogram (LSP) method to search for significant periods, and further validate them using the Weighted Wavelet Z-transform (WWZ) method for time-frequency domain analysis. Finally, based on Schwarzschild black hole (a=0) and extreme Kerr black hole (a=0. 998 2) models, we estimate the mass of the central black hole of this blazar. We obtain black hole masses of 1. 11 × 109 M☉ (Schwarzschild black hole) and 7.07 × 109M☉ (extreme Kerr black hole) with a main period of 7.4 days.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-17 Cooperative journals: 《天文研究与技术》
Abstract: The variability is one of the most fundamental observational features of Blazars, the generation of Intra-Day Variability (IDV) is still a controversial issue. In this paper, we combine the 4LAC-DR2 catalog with the fifth Roma-BZCAT catalog to study the characteristics of mid-infrared IDV of different classes of Blazars using data from the ALLWISE project. The results show that: (1) The IDV of Low Synchrotron Peaked Blazars (LSPs) exhibit larger variability amplitudes compared to Intermediate Synchrotron Peaked Blazars (ISPs) and High Synchrotron Peaked Blazars (HSPs); (2) The IDV of Flat Spectrum Radio Quasars(FSRQs) also exhibit larger variability amplitudes compared to BL Lacertae objects (BL Lacs), and the color changes of both tend to become bluer when brighter; (3) The IDV of Fermi-detected Blazars exhibits a smaller variability amplitude compared to Non-Fermi ̄detected Blazars. Based on the study of the above results, we suggest that Blazars′ observed emission in the mid-infrared band may come from a spatial scale range of ~10-4 pc, that its IDV production may be related to physical processes intrinsic the jet, and that the amplitudes of the IDV may be closely related to the synchrotron peak of the Spectral Energy Distribution (SED).
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 2021-11-12 Cooperative journals: 《天文研究与技术》
Abstract:Owens Valley Radio Observatory (OVRO)40米望远镜的观测数据显示了BL Lac 天体 CGRaBS J0141-0928在15 GHz射电波段的剧烈光变. 我们利用Lomb-Scargle-Periodogram (LSP)方法和加权小波Z变换(Weight Wavelet Z-transform,WWZ)方法以及Jurkevich方法分析了CGRaBS J0141-0928的光变周期, 结果显示该天体具有约为649天的准周期振荡(Quasi-Periodic OScillation, QPO), 其置信度为4.4σ, 其准周期振荡可能是由喷流的螺旋运动产生. 我们用双指数函数拟合了其中2 个爆发的过程, 从而得到其光变时标, 进而估算其平均多普勒因子为3.8, 这表明CGRaBS J0141-0928 在射电辐射波段存在显著的聚束效应. 采用DCF(Discrete Correlation Function) 方法对射电波段分别与Gamma-ray、光学 R 波段的光变相关性进行分析, 发现光学光变与射电光变有强相关性,且光学光变超前于射电光变66±40天.
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 2020-07-10 Cooperative journals: 《天文研究与技术》
Abstract:基于Owens Valley Radio Observatory (OVRO) 40米望远镜观测数据,我们收集了耀变体CGRaBS J0835+6835在15GHz射电波段的数据(约12年)。利用Lomb-Scargle periodogram (LSP)方法和加权小波Z变换(Weight Wavelet Z-transform,WWZ)方法,我们检测到了CGRaBS J0835+6835存在一个约560天左右的准周期震荡(Quasi-periodic oscillation,QPO)。我们运用超大质量双黑洞系统中的螺旋喷流模型,估算了它的主黑洞质量M的范围约为3.7×108M⊙~3.5X109 M⊙。为了探究此源是否存在聚束效应,我们使用双指数函数拟合6个爆发过程,发现光变多普勒因子δV的平均值约为10.76。这表明此源的射电辐射存在明显的聚束效应。
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 2019-09-18 Cooperative journals: 《天文研究与技术》
Abstract: 使用了一个具有(准)同时性宽带能谱数据的Fermi耀变体样本,对其进行了同步和逆康普顿峰峰值参量、康普顿主导以及高能谱指数等参量之间的相关性分析。以获得耀变体整体和子类相关性之间差异来源、耀变体喷流中粒子冷却的主导机制,和电子能谱形状等方面的解释。分析结果表明耀变体的整体相关性至少有部分来自于平谱射电类星体和BL Lac天体由于物理性质不同而在参数平面上具有不同分布区域这一特性贡献,因此针对两个子类的相关性分析是必需的。BL Lac天体为快冷却机制。谱指数图的结果支持对数抛物线形状的电子能谱。
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 submitted time 2018-09-13 Cooperative journals: 《天文研究与技术》
Abstract: 本文利用UMRAO数据库的22个耀变体源的偏振数据,根据Lazarian & Pogosyan的理论模型进行分析研究了耀变体射电波段的偏振随波长的变化,得出不同类的耀变体偏振随波长的变化的原因。其结果表明,与Lazarian & Pogosyan的理论模型吻合较好。由此我们得出如下结论:(1)反常去偏振耀变体源中反常法拉第旋光起主导作用,反常去偏振相对较少;(2)热辐射与同步辐射混合作用,高频波段的偏振度就小于低频波段的偏振度(反常去偏振);(3)当被观测波段波长小于吸积盘热辐射所对应的维恩波长时,高频波段的偏振度就大于低频波段的偏振度(常规去偏振)。