An Analysis of Light Periods of BL Lac Object S5 0716+714 with the MUSIC Algorithm

The multiple signal classi?cation (MUSIC) algorithm is introduced to the estimation of light periods of BL Lac objects. The principle of the MUSIC algorithm is given, together with a testing on its spectral resolution by using a simulative signal. From a lot of literature, we have collected a large number of effective observational data of the BL Lac object S5 0716+714 in the three optical wavebands V, R, and I from 1994 to 2008. The light periods of S5 0716+714 are obtained by means of the MUSIC algorithm and average periodogram algorithm, respectively. It is found that there exist two major periodic components, one is the period of (3.33±0.08) yr, another is the period of (1.24±0.01) yr. The comparison of the performances of periodicity analysis of two algorithms indicates that the MUSIC algorithm has a smaller requirement on the sample length, as well as a good spectral resolution and anti-noise ability, to improve the accuracy of periodicity analysis in the case of short sample length.     

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.     

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.     

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.     

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.     

An Analysis of the Radio Light Variations of Blazars With Low Peak Frequencies

The data of light variations of six blazars with low peak frequencies (i.e., BL Lacerta, 0235+164, OQ530, 0716+714, 3C 345, and 3C 273) at 4.8, 8, 14.5, 22 and 37 GHz in the recent thirty years have been collected from immense amount of literature. By using the method of discrete correlation function the correlations and delays of the light curves of these six sources at the 5 wavebands are analyzed. With the method of structural function, the periods and timescales of the light variations of these six sources are analyzed, and their amplitudes of light variations are compared and analyzed. As revealed by the result of analysis, among the six blazars the amplitudes of light variations of 0716+714 and 0235+164 are relatively large, and those of 3C 345 and OQ 530 are less. The amplitudes of light variations of 3C 273 and BL Lacertae are relatively smaller. As shown by the multi-waveband analysis of delays between two neighboring wavebands, 0235+164 exhibits the tendency of variation that the high-frequency wavebands precede the low-frequency wavebands. On the whole, 3C 345 exhibits the tendency that the high-frequency wavebands lag be-hind the low-frequency wavebands. The analyses of the other blazars show that in a part of radio wavebands there appears the tendency of variation that the high-frequency waveband leads the low-frequency waveband. Yet in the other radio wavebands there appears the tendency that the high-frequency waveband lags behind the low-frequency waveband. As revealed by the results of analyses with the method of structural function, the timescale, fitted slope, and period of light variations of 3C 345 are larger than those of the other five blazars with low peak frequencies. This demonstrates that the activity of 3C 345 is comparatively weaker than the other five sources, and implies that in the interior of 3C 345 there may exist some physical processes which are different from those of the other five blazars with low peak frequencies.     

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.     

Chaotic Behaviour of Intra-Day Variability of BL Lac Object S5 0716+714

An optical monitoring shows Blazar object S5 0716+714 has complex Intra-Day Variability (IDV) behaviour. In this paper, we introduce a method of non-linear time series analysis, and calculate the correlation dimension of the IDV light curves of S5 0716+714 over seven nights in the December of 2006. According to our calculations, the correlation dimension D ≈ 1.993 ? 5.178 for all of the observed data, it is implied that the IDV behaviour may be a chaotic system with some additional noise.     

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.     

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.     

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.     

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.     

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...     

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.     

致密射电源短时标变化的相对论效应

本文讨论相对论激波在喷流中传播时,由照明不均匀性所引起的同步加速辐射问题中的某些相对论效应.研究激波的结构和厚度以及不均匀性尺度对于辐射变化的时标和变幅的关系.结果表明,由于激波辐射区的厚度对于光学辐射和射电辐射的不同,可能引起射电变化相对于光学变化的时间迟延,从而对某些观测现象提供了一种解释.     

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.     

Optical Photometric Observations of 7-Ray Loud Blazars

We report results of our optical photometric observations of ten gamma-ray loud blazers, namely: 0219+428 (3C66A), PKS 0420-014 (OA 129), S5 0716+714, 0754+100 (OI 090.4), 0827+243 (OJ248), 1652+398 (Mrk 501), 2200+420 (BL Lacertae), 2230+114 (CTA 102), 2251+158 (3C 454.3) and 2344+514. The observations were carried out in September-October, 2000 using the 70 cm optical telescope at Abstumani Observatory, Georgia. We found intra-day variations in 0420-014, S5 0716+714, BL Lacertae and CTA 102. A variation of 0.3 magnitude over a time scale of about 3 hours was observed in the R passband in BL Lacertae on JD 2451827. We did not detect any variation in 3C 66A, Mrk 501, or 3C 454.3 during our observations. Nor did we detect any clear evidence of variation in 1ES 2344+514 during our two weeks' observing run of the TeV gamma-ray source.     

Synchrotron self-Compton models of high brightness temperature radio sources

We re-examine the maximum brightness temperature that a synchrotron source can sustain by adapting standard synchrotron theory to an electron distribution that exhibits a deficit at low energy. The absence of low energy electrons reduces the absorption of synchrotron photons, allowing the source to reach a higher brightness temperature without the onset of catastrophic cooling. We find that a temperature of ∼10¹⁴ K is possible at GHz frequencies. In addition, a high degree of intrinsic circular polarisation is produced. We compute the stationary, synchrotron and self-Compton spectrum arising from the continuous injection of such a distribution (modelled as a double power-law) balanced by radiative losses and escape, and compare it with the simultaneously observed multi-wavelength spectrum of the BL Lac object S5 0716+714. This framework may provide an explanation of other high brightness-temperature sources without the need for mechanisms such as coherent emission or proton synchrotron radiation.     

AO 0235+164射电波段宽带谱指数周期性变化的研究

收集了AO 0235+164天体射电4.8 GHz和14.5 GHz波段的光变测量数据,并获得了长期的光变曲线,从光变曲线可以看出其活动是非常剧烈的。利用Jurkevich方法和自相关函数方法分别对AO 0235+164射电波段宽带谱指数进行周期性分析,并对流量和谱指数进行相关性分析,研究结果表明:(1)AO 0235+164天体射电波段4.8 GHz～14.5 GHz对应的宽带谱指数,可能存在5.30年的光变周期,与Liu等人用功率谱法在射电波段发现其流量密度可能存在5.59±0.47年的光变周期基本吻合;(2)宽带谱指数与流量密度之间存在相关性。     

Rms-flux relation in the optical fast variability data of BL Lacertae object S5 0716+714

The possibility that BL Lac S5 0716+714 exhibits a linear root mean square (rms)-flux relation in its IntraDay Variability (IDV) is analysed. The results may be used as an argument in the existing debate regarding the source of optical IDV in Active Galactic Nuclei. 63 time series in different optical bands were used. A linear rms-flux relation at a confidence level higher than 65 % was recovered for less than 8 % of the cases. We were able to check if the magnitude is log-normally distributed for eight timeseries and found, with a confidence ≥95 %, that this is not the case.