利用MUSIC算法分析BL Lac天体S5 0716+714光变周期

将基于多重信号分类的MUSIC谱估计算法引入BL Lac天体光变周期分析中.给出了MUSIC算法的基本原理,利用模拟信号检测了算法的频谱分辨率.从大量文献中收集了BL Lac天体S5 0716+714光学V、R、I 3个波段从1994年到2008年的有效观测数据,用MUSIC算法和平均周期图算法分别计算了它们的光变周期,发现存在两个主要光变周期:一个是(3.33±0.08)yr的周期,另一个是(1.24±0.01)yr的周期.对这两种算法的周期估计性能进行了比较,结果表明,MUSIC谱估计算法对样本长度要求较低,具有良好的分辨特性和抗噪声能力,能提高在样本长度较短情况下光变周期分析的准确性.     

Calculating the Light Period of BL Lac Object S5 0716+714 by Wavelet Analysis Method

A kind of wavelet analysis method for identifying the light period of the BL Lac object S5 0716+714 is introduced. The rather complete observed data in the four optical wavebands B, V, R, I are collected, and the long-term light curves based on 10-day averaging are obtained. On these light curves, the periodicity analysis is performed by using a wavelet analysis method. The result demonstrates that the wavelet analysis method is preferable for searching and identifying the light periods of BL Lac objects. From the contour map of the real part of the wavelet transform coefficient, the periodical light variations of the BL Lac object S5 0716+714 can be precisely identified. By analyzing the wavelet variance curves at the 4 wavebands, it is found that the BL Lac Object S5 0716+174 has a stable light period of 1160 days. This result is consistent with the 3.3-year period given by Raiteri et al. It is predicted that the next outburst in this object will happen around the August of 2011.     

Analyses of the Light Variations of OJ 287, 0716+714 and BL Lacertae

OJ 287 is a BL Lac object which exhibits intense activities of low peak-frequencies. Its energy spectrum in low frequency band is quite similar with those of two other TeV BL Lac objects (i.e., 0716+714 and BL Lacertae). However, the Cerenkov telescope did not detect its TeV rays. By using the observational data of these three heavenly bodies and comparing the discrepan- cies of their minimal periods of light variations and delays at 22 GHz, 37 GHz and B-waveband, we have further investigated the possible reason why the TeV gamma-rays of OJ 287 have not been observed. The results of analyses are as fol- lows. (1) For the minimal periods of light variations, the periods of OJ 287 at 37 GHZ and B-waveband are short. At 22 GHz the results of OJ 287 and 0716+714 are comparable, but the period of OJ 287 is much shorter in comparison with that of BL Lacertae, and this shows that its activity is more intense. However, the TeV gamma-rays of OJ 287 have not been detected, which implies that the radiation of OJ 287 in TeV waveband may have no connection with the minimal periods of light variations in these three low-energy wavebands. (2) In respect of delays, the delay of OJ 287 in the B waveband with respect to 37 GHz is longer than that of 0716+714, but shorter than that of BL Lacertae. Its delay at 37 GHz in respect to 22 GHz is shorter than that of 0716+714. Meanwhile, the delay of BL Lacertae at 37 GHz in respect to 22 GHz is negative, which implies that 22 GHz precedes 37 GHz. Via the comparison and analysis of delays, no obvious differences between OJ 287 and 0716+714 as well as BL Lacertae have been found. On the side of energy spectra, it is quite possible that due to the steep energy spectrum of OJ 287 in TeV waveband, the Cerenkov telescope has not detected the gamma radiation of OJ 287. However, nowadays it is still not clear whether the steep energy spectrum in TeV energy range has some influence on the light variations in low energy realm.     

Computing the Periods of Light Variation of Blazar Objects 3C279 and OJ 287 with Autoregressive Spectral Analysis Method

The light variability is one of the main characteristics of blazar objects. Because of the complexity of their light curves, the present periodicity analysis methods are not yet perfect. Based on the modern spectral estimate theory, this paper has described in details the principles of the maximum entropy spectral estimate and autoregressive (AR) spectral estimate, analyzed the effect of the order number selection on the resultant model. Applying these methods to the periodicity analysis of the quasar 3C 279 and BL Lac object OJ 287, their light periods are obtained to be 7.14 and 11.76 yr, respectively. As is verified by experiments, the AR spectral estimate has a high resolution and is a rather good periodicity analysis method. Finally, the items noteworthy for the application of these spectrum estimation methods to the periodicity analysis of the light variations of blazars are mentioned.     

The Long-term Light Variation of BL Lac Object 1ES 1959+650

According to the data of optical observations of the Tuorla Observatory in Finland, using the power spectrum method, DCF (Discrete Correlation Function) method, and Jurkevich method, respectively, we analyzed the periodicity of the long-term light variation of the BL Lac object 1ES 1959+650, and obtained its light period to be P =1.4±0.3 yr. Assuming that the origin of the periodicity is concerned with the accretion disk, we obtained the region where the instability of this source occurs being R =9.65 R_g, here R_g represents the Schwarzschild radius.     

A Study on the Multi-band Radiation Mechanism of Mark 421

Based on the log-parabolic spectral energy distribution of electrons, and the homogeneous one-zone synchrotron self-Compton (SSC) model, the multiband spectral energy distribution of the BL Lac object S5 0716+714 is calculated. Compared with Paggi's result which is obtained by means of δ-function approximation, it is found that a certain difference exists between our result and Paggi's. The main reason leading to this difference may be that the δ-function approximation on the synchrotron radiation of a single electron loses a part of electron energy, and therefore affects the result of inverse Compton scattering. Applying this model to the results of the multi-band observations made at three different states of Mark 421: high, medium, and low, the results of theoretical calculations are coincident very well with the observational results under the three different states of the object. An analysis indicates that the observed different states of Mark 421 are probably caused by the variation of the electron distribution in the jet.     

OJ 287,0716+714与BL Lacertae的光变分析

OJ 287是存在着剧烈活动的低峰频BL Lac天体,其低频段的能谱与另两个TeV BL Lac天体(0716+714和BL Lacertae)在低频段的能谱很相似,但是切仑科夫望远镜却没能探测到它的TeV射线.利用这3个天体的观测数据,比较它们在22 GHz、37 GHz和B波段的最小光变周期及延迟的异同,进一步寻找没有观测到OJ 287的TeV伽马射线的可能原因.分析结果显示:(1)最小光变周期方面,OJ 287在37 GHz和B波段的周期偏小,在22 GHz,OJ 287与0716+714的结果相当,但与BL Lacertae相比要小很多,OJ 287的周期更短表明其活动性更强,却没有探测到来自OJ 287的TeV伽马射线,这表明OJ 287在TeV波段的辐射与这3个低能波段最小光变周期之间可能没有联系;(2)延迟方面,OJ 287在B波段相对于37 GHz的延迟要长于0716+714,短于BL Lacertae;在37 GHz相对于22 GHz的延迟要短于0716+714,而BL Lacertae在37 GHz相对于22 GHz的时延为负值,表明22 GHz要超前于37 GHz.通过对延迟的比较分析,并没有发现OJ 287与0716+714和BL Lacertae之间存在明显的差异;从能谱来看,很可能是由于OJ 287在TeV波段的能谱较陡造成切仑科夫望远镜没有探测到来自OJ 287的伽马辐射,但TeV能段较陡的能谱对低能段光变的影响目前还不是很清楚.     

Optical Monitoring of bright Blazars with Automatic Telescopes

Well sampled light curves of BL Lac objects are very useful to understand the physical processes responsible for the highly variable emission from this class of AGN. The best way to perform the necessary high number of observations is the use of automatic small aperture telescopes. We present some results of the Perugia-Roma monitoring program concerning the recent active phase of BL Lac and the Intra-Day Variability of S5 0716+714. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectral Evolution of Synchrotron and Inverse Compton Emission in BL Lac Objects

With XMM–Newton observations, the X-ray spectral variations and the derived physical implications for two very high energy gamma-ray BL Lac objects PKS 2155–304 and S5 0716+714 are presented.     

IDV Observations of BL 0716+714 at 5 GHz

A selected sample of intra-day variable AGN had been observed for 3–4 days per month at the Urumqi Observatory. The sample includes 7 target sources and 7 calibrators. The BL Lac object B0716+ 714 shows prominent intraday and long term variations.     

基于自回归方法的Blazar天体3C 279和OJ 287光变周期研究

探索Blazar光变资料中的周期或准周期变化是1个有待深入研究的领域.由于光变资料的复杂性,目前寻找周期的算法还不够完善.文中以现代谱估计为基础,详细论述了自回归(Auto-regressive,AR)模型谱估计方法和最大熵谱估计的基本原理,分析了阶数选择对模型的重要影响,并把这些方法应用到类星体3C 279和BL Lac天体OJ287的光变周期分析中,得到它们的光变周期分别为7.14和11.76yr.通过验证,自回归 模型谱估计方法由于其分辨率高,可以作为1种较好的分析周期的方法.最后指出在应用谱估计分析Blazar天体的光变周期注意事项.     

用Jurkevich方法分析计算BL Lac天体的光变周期

本文介绍一种分析寻找ＢＬＬａｃ天体光变周期的方法,给出了ＢＬＬａｃ天体ＯＪ２８７,ＯＮ２３１,Ｍｒｋ４２１的长光变周期．分析计算表明：当观测样品的数据点很多、观测时间很长（大约１００年左右的光学波段数据）、数据样本不少于６个周期并能从光变曲线的两次大振幅中,看出有若干小振幅的周期时,则能用该方法准确地认证和确定其长周期值．这种方法在寻找周期时,对无规律不等间隔的样品数据有较高的灵敏度,而计算方法简捷实用,结果可靠     

Evolution of optical spectral index and variability properties of S5 0716+714

We analyze the spectral variability and spectral evolution in the optical energy region by using multiband (BVRI) optical observations of S5 0716+714 spanning 1994 to 2005. The spectrum hardens when the source becomes brighter, which is consistent with general BL Lac objects. The spectral evolution parameter implies that the spectral variability is small in optical bands over 10 years. A simple model representing the variability of a synchrotron component can explain the spectral changes. In addition, we em...     

Computing the Light Periods of Blazars with the Periodogram Spectral Analysis Method

The periodogram spectral analysis method applicable to equallyspaced time series is discussed, and the method is tested first with a simulated data series. It is confirmed that this method is effective for noisy series. Then, applying this method to the analysis of the light periods of the quasars 3C 279 and 3C 345 as well as the BL Lac objects OJ 287 and ON 231, we obtain their light periods to be 7.14 yr, 10.00 yr, 11.76 yr and 6.80 yr, respectively. These results obtained by periodogram spectral analysis are consistent with those obtained by the Jurkevich method in the literature. We have analyzed the effects of different window functions, and commented on their correct selection in practical applications.     

New statistical results on the optical IDV data of BL Lac S5 0716+714

This paper reports on the statistical behavior of the optical Intraday Variability of BL Lac S5 0716+714. Available Intraday Variability data in the optical are tested to see whether or not the magnitude is lognormally distributed. Our results consistently indicate that this is not the case. This is in agreement with a previous discussion about data for the same object but in a different observational period.Simultaneously, the spectral slope of the light curves is calculated. The implications of these findings on models that describe both the location and source of Intraday Variability are presented.     

The Optical Microvariability and Spectral Changes of the BL Lacertae Object S5 0716+714

The BL Lac object S5 0716+714 was monitored in the optical band during October 2008, December 2008 and February 2009. We achieved a best temporal resolution of about 5 min in the BVRI bands. The source was active during the whole monitoring campaign. It showed microvariability in 13 days out of 14 days of observation. Four fast flares were observed with amplitudes ranging from 0.3–0.75 mag. The overall amplitude changes during the whole campaign are ΔB ~ 0. ^m 89, ΔV ~ 0. ^m 80, ΔR ~ 0. ^m 73, and ΔI ~ 0. ^m 51. On internight time scales, strong bluer-when-brighter chromatism was found while different spectral behaviours were found on intranight time scales.     

The Periodicity Analysis of Radio Flux Variability of PKS 1510-089 with the Period04 Method

We have collected the 37 GHz radio data of PKS 1510-089 from 1990 to 2005, and obtained its long-term light curve after making data processing. From the light curve we can find that the activity in PKS 1510-089 is very strong. In this paper, the Period04 method is used for the first time to analyze the light periodicity of PKS 1510-089. The result indicates that its radio emission at 37 GHz has the periods of (1.87±0.13) yr and (0.87±0.07) yr. This result is consistent with the results obtained by Xie et al. in 2004, 2005, 2008, and Wu et al. in 2005 with other methods of data analysis.     

耀变体光学波段的微光变及能谱变化

耀变体在多个波段的微光变和能谱变化多年来是中外天文观测研究的热点课题.耀变体的微光变于20世纪60年代被发现,20世纪80年代以来发现很多源的微光变具有不同的特性,目前对其物理机制的认识和理论、模型的研究还处于发展阶段.该文总结了7个目前观测最多的耀变体(3C 66A,3C 279,3C 454.3,AO 0235+164,BL Lac,OJ 287,S5 0716+714)在光学波段的微光变和能谱变化的观测历史和最新进展,并对其理论模型作了简单介绍.     

Power Spectrum Density of Stochastic Oscillating Accretion Disk

In this paper, we employ a stochastic oscillating accretion disk model for the power spectral index and variability of BL Lac object S5 0716+714. In the model, we assume that there is a relativistic oscillation of thin accretion disks and it interacts with an external thermal bath through a friction force and a random force. We simulate the light curve and the power spectrum density (PSD) at (i) over-damped, (ii) critically damped and (iii) under-damped cases, respectively. Our results show that the simulated PSD curves depend on the intrinsic property of the accretion disk, and it could be produced in a wide interval ranging from 0.94 to 2.05 by changing the friction coefficient in a stochastic oscillating accretion disk model. We argue that accretion disk stochastic oscillating could be a possible interpretation for observed PSD variability.     

Long-Term Optical Spectra Variability of BL Lacertae Object S5 0716+714

Based on the long-term data from observations, we present an evidence for its spectral index variability behaviour in optical bands for BL Lacertae object S5 0716+714. We find that the spectral index variability period is in agreement with the flux variability period of about 1180 days in optical bands. We also find that the spectral index variability has periods of about 71 and 60 days which cannot be compared with the amplitude of long-term variability.