Transient quasi-periodic oscillations (QPOs) are extremely interesting observational phenomena. However, the precise physical mechanisms leading to their generation are still hotly debated. We performed a systematic search for transient QPO signals using Weighted Wavelet Z-transforms on the gamma-ray light curves of 134 bright blazars with peak flux exceeding $1\times10^{-6}$~ph~cm$^{-2}$~s$^{-1}$ as monitored by Fermi-LAT. Artificial light curves were generated from the power spectral density and probability distribution functions of the original light curves to assess the significance level of transient QPO. We discuss several physical mechanisms that produce transient QPOs, with the helical jet model providing the best explanation. This study identified four new transient QPO events. Interestingly, repetitive transient QPOs are observed in PKS 0537-441, and nested transient QPOs are detected in PKS 1424-41. Additionally, we find that transient QPOs tend to occur in the flare state of the blazar. Finally, we estimate the incidence of transient QPO events to be only about 3\%.

The blazar PG 1553+113 is hypothesized to harbor a supermassive black hole binary system, a scenario that aligns with its observed physical characteristics. In this study, we re-examine the authenticity of the periodicity of PG 1553+113 by conducting a comprehensive analysis of multi-wavebands periodic light variations, using the updated light curve data of more than 15 years. We used two methods to search for the light curves data of this blazar in gamma-ray, X-ray, optical and radio bands. The multi-wavebands analysis approach enables a thorough verification of the observed periodic patterns. The result of gamma-ray detection showed a quasi-periodic oscillation (QPO) of 2.16 years, which verified the results given by Ackermann et al. (2015). And the optical band shows a QPO of 2.24 years. We analyzed the correlation among gamma-ray, optical and radio bands, and we found that there is a strong correlation among them, and the emission of different bands coming from the same region (the same electron group). Finally, we estimated the black hole mass of PG 1553+113 to be M similar or equal to 4.3 x 10(9) M-circle dot based on the binary black hole model.

光变是耀变体(Blazar)的重要观测特征.为了研究耀变体的多波段光变特征,收集了 Fermi(LAT),中小型口径研究望远镜系统(Small and Moderate Aperture Research Telescope System,SMARTS),SWIFT(XRT)和亚毫米波阵列(Submillimeter Array,SMA)发布的PKS 1424-41 在γ波段(0.1～100 GeV)、光学R波段、近红外K波段、X波段和射电波段的流量或星等值.用离散相关函数(Discrete Correlation Function,DCF)对各个波段光变曲线间进行相关性分析,结果表明,γ波段、X波段、光学R波段、近红外K波段和射电波段彼此间存在强相关性,各波段之间存在时间延迟.该结果支持同步辐射模型.利用 LSP(Lomb-Scargle Periodogram)方法分析了PKS 1424-41 的γ波段在一个爆发时间段(MJD 56100-56500)的光变曲线准周期振荡(Quasi-Periodic Oscillations,QPO),发现它在这个时间段具有～75 天和～50 天两个准周期振荡,比值为3∶2.喷流自身的螺旋结构及在其中运动的高能等离子体团块的辐射,可能是这类月量级准周期振荡的起源.

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,(α rw1 , α rw2 , α rw3 , α ro , α rγ , α w1w2 , α w1w3 ) and α w3x , 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%.

凌日系外行星巡天卫星(Transiting Exoplanet Survey Satellite，TESS)观测到的耀变体PKS 0422+004(α =04 24 46. 8421990080，δ =+00 36 06. 329375028)的光学波段光变曲线在第32扇区存在约7.4天的准周期振荡( Quasiperiodic Oscillation, QPO)。 使用LSP( Lomb Scargle Periodogram)方法寻找显著性周期，并用加权小波Z变换(Weight Wavelet Z-transform，WWZ)方法进行时频域分析进一步验证。最后，基于施瓦西黑洞(a =0)和极端克尔黑洞(a =0. 998 2)两种模型，估算了这个耀变体中心黑洞的质量。以7. 4天为主周期， 得到黑洞质量分别为1. 11 × 109M☉(施瓦西黑洞)和7. 07 × 109M☉(极端克尔黑洞)。

We systematically search for quasiperiodic oscillatory (QPO) signals on the month timescale among the 1525 sources given in the Fermi Large Area Telescope Light Curve Repository. We find a transient QPO of 31.3 ± 1.8 days in the gamma-ray band light curve of the TeV blazar S5 0716+714, which has seven cycles (MJD 55918–56137) for the first time by weighted wavelet Z-transform and Lomb–Scargle periodogram methods. Monte Carlo simulations based on the power spectral density and probability distribution function were used to evaluate the confidence level of the QPO, and the result is ∼4.1σ. Seasonal autoregressive integrated moving average modeling of the light curve revealed it is a significant physical QPO. The physical models to explain the sporadic month-timescale QPOs in the blazar were discussed. Our studies indicate that the helical jet model and blob move helically in a curved jet model to properly explain this kind of transient QPO.

利用LSP（Lomb-Scargle Periodogram）方法和加权小波Z变换（Weight Wavelet Z-transform, WWZ）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1 435天（3.93年）和1 321天（3.62年）,且置信度均＞3σ（99.7%）,而在伽马波段的光变周期性较弱。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M分别为4.3×10~9M ⊙ 和2.7×10~9M ⊙ 。为了探讨射电和伽马波段的光变起源，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，表明它们的辐射可能来自不同的区域。