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1.
展示活动星系核研究和引力研究中的一些难点,揭示了某些天体的光主存在分形结构的可能性,我们提出了活动星系核的中心黑洞具有某种随机微活动性的假设,该假设在可解释活动星系核的一些观测现象。我们发现Ｗｅｉｅｒｓｔｒａｓｓ函数的分形图形可以用来很地拟合ＯＪ２８７的短时标光变。一个用Ｗｅｉｅｒｓｔｒａｓｓ函数构造的分形曲线与ＯＪ２８７的历史光变的线性相关系数达以了０．７３,我们计算了ＯＪ２８７光变曲线的计盒维 相似文献
2.
分析了１９９３－１９９５年ＢＬＬａｃ、ＯＪ２８７和ＰＫＳ０７３５＋１７８三颗ＢＬＬａｃ天体光变的监测结果,并结合文献上他人发表的资料,发现一些ＢＬＬａｃ天体处于高态时活动性较强,短时标光变频繁发生,而处于低态时活动性较弱,短时标光变很少发生．文中提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型能够解释ＢＬＬａｃ天体短时标光变行为在高态和低态下的差别,并能很好地解释Ｔａｋａｌｏ等人监测ＯＪ２８７时发现的新现象． 相似文献
3.
分析了１９９３－１９９５年ＢＬ Ｌａｃ、ＯＪ２８７和ＰＫＳ０７３５＋１７８三颗ＢＬ Ｌａｃ天体光变的监测结果,并结合文献上他人发表的资料,发现一些ＢＬ Ｌａｃ天体处于高态时活动性较强,短时标光变频繁发生,而处于低态时活动性较弱,短时标光变很少发生。文中提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型能够解释ＢＬ 相似文献
4.
活动星系核有两种主要的光变:不规则的闪耀和比较有规律的周期性光变,不规则光变的典型的时间尺度是10~4—10~5秒,周期性光变的典型的时间尺度是10~6—10~8秒。这篇综述主要讨论基于活动星系核黑洞吸积模型上的一些光变模型。这些讨论表明,活动星系核的短时标光变特征对厚吸积盘模型提供了强有力的支持。对时标较长的周期性光变,尽管现在已有不少模型(“亮斑”、薄盘的不稳定性、双稳定性、自引力吸积盘的脉动等等),但是所有这些模型都不够完善;当然也有些模型是很有希望的(如双稳定性)。 相似文献
5.
宇宙学的基本假设之一是宇宙在大尺度上均匀各向同性.为了验证星系分布在大尺度上的均匀性,分别计算观测样本和观测空间几何体的分形维数,得到SDSS-DR4中星系分布的分形维数.观测空间几何体的分形维数用随机样本来确定.样本中的星系红移z的范围为0.01-0.26.当尺度持续增加至几十个Mpc时,星系分布的分形维数一致地趋向于3.所有的样本均显示了明显的转变尺度,当尺度大于此转变尺度时,星系分布的分形维数D<,G>～3,星系的分布转变为均匀分布.结果支持了宇宙学的基本原理关于宇宙大尺度均匀的假设.样本的转变尺度随着样本的光度增强而变大,说明小尺度上星系的分布不是简单的分形分布,而是多维分形分布.高光度星系的转变尺度非常大,直到100h-1Mpc左右才变得均匀. 相似文献
6.
探索活动星系的快速光变,是研究星系中心致密核结构及辐射机制的强有力手段。NGC4051是在X射线波段具有短时标(分—小时)光变的极少数活动星系之一。为进一验证X射线波段短时标光变的观测结果,也为了探索光学波段是否具有短时标光变及它们的相关性,我们于1985年5月13—15日分别在美国和中国对NGC4051进行了X射线波段及可见光波段的同时性联测。Martin博士和程福臻在美国利用EXOSAT卫星观测了NGC4051的X射线辐射;谢光中等人在云南天文台利用一米RCC望远镜及积分光度计进行了U波段的观测。结果如下:(1)软X射线的流量降低了13倍,而硬X射线的流量已小到探测不到(至少降低了203倍);(2)U波段在13日晚的观测表明NGC4051有一个时标～1200秒、振幅ΔU 0.11(±0.03)的短时标光变。这种光变共有四个事例,且光变曲线十分完整,由于标准误差σ=0.03,可信度已大于3σ。此外,这一结果还与P.E.Marshall等人在X—射线波段所得到的光变时标～1000秒相吻合,这似乎表明两个波段的光变可能具有相关性。 相似文献
7.
本文综述了活动星系核 ,特别是blazar天体的研究现状 ,对blazar天体的多波段与多波段能谱特性研究进行了较为详细的评述。主要的研究工作包括以下内容 :(一 )γ噪blazar天体的短时标光变研究 ,通过对 1 6个γ噪blazar天体 (其中包括全部已证认和观测到VHEγ射线爆发的可能甚高能γ射线源 )自 1 998年的光学观测及光变分析研究表明 ,短时标光变 (小时量级 )是GeVγ噪blazar天体的普遍特性 ,光变幅度通常可达 0 .6mag/h ,对PKS 1 51 0 -0 89类星体的观测发现在一个小时内对象变暗 2个星等 ,对如此激烈的光变变暗目前的理论还不能很好的解释 ,但它同样反映了辐射区域的内部结构 ;而对TBLs的监测表明 ,其光学波段的短时标光变没有其他对象激烈 ,出现的频度和振幅变化都较小 ;(二 )在研究γ噪blazar天体光变时 ,研究了寄主星系对光变的影响 ,得到了 1ES 2 3 44 + 51 4的光变与PSF的FWHM的关联 ,表明随着大气视宁度的下降 (即FWHM变大 ) ,对象变暗 ,即由于寄主星系的影响从而导致假光变的产生 ;(三 )引进两个多波段复合谱指数 ,αxox=αox-αx 及αoro=αor-αo。对样本的统计研究表明 ,RBLs是能谱特性界于XBLs和OVVs之间的一类中间态 ,所得结果支持了Sambrunaetal.( 1 996)大样本多波段能谱分布特性的统计研 相似文献
8.
活动星系核中的铁K线辐射可由X射线照射的冷物质 ,热等离子体产生 ,它提供了活动星系核从非常核心到核周围的物质分布 ,物理状态 ,以及中心黑洞强引力场的重要诊断手段。本文我们评述活动星系核中铁K线形成的物理和最近的观测进展 相似文献
9.
密度波理论中星系激波的解大都假设为局部的,并且往往不考虑星际气体自引力的影响。本文取消了上述两个假设条件,求解了二维不定常气体动力学方程组,其中包括了星际气体的自引力效应。研究了在外加扰动螺旋引力场的作用下,轴对称气体盘中星系激波的形成过程。得到了星系激波的运动和密度分布特征。与非自洽的局部激波解相比,两者的定性特征相似,但定量结果有较大差别。计算表明,星系激波宏图的图样速度随时间和空间而变化,变化的大小甚致超过了外加密度波的图样速度。形成星系激波的特征时间约为5×10~8年。由于激波宏图与外加密度波宏图的相对缠卷,难于维持准稳恒的星系密度波,但每一具体时刻仍有大尺度的星系激波宏图。 相似文献
10.
耀变体是一类喷流与视线方向近似平行的活动星系核,高偏振是其区别于其他活动星系核的一个典型特征。耀变体的偏振一般认为是由喷流中相对论电子的同步辐射产生的。通过对光学偏振的观测,可以充分约束喷流性质,也给其他波段的光变信息提供补充。主要介绍耀变体光学偏振的研究情况:首先介绍耀变体及其偏振的一些背景;随后介绍耀变体偏振产生的原因、耀变体的去偏振效应、耀变体偏振随波长变化的研究,以及高能耀发与光学偏振相关性研究;最后,对耀变体光学偏振研究进行展望。 相似文献
11.
We have studied the optical historical light curves of two Active Galactic Nuclei (AGNs): OJ287 and 3C345. We find a linear
dependence between the magnitude and the logarithm of the length of the time the objects stay below this magnitude. The relation
may originate from a fractal structure of the light curve.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
A Fourier series fitting of order 10 to the historical light curve of OJ287 (3648 data points) is presented with correlation
coefficient ∼ 0.73. It is found that the Weierstrass function may be used to imitate the short time scale variability of OJ287.
A fractal curve constructed by the function possesses the similar correlation coefficient to the light curve as the regression
curve. We also calculate the capacity-dimension, information-dimension and correlation-dimension of the light curve. The calculations
indicate that their values > 1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Considering the shortages of classical methods in periodicity analysis, the method of empirical mode decomposition (EMD) for processing nonlinear and non-stationary signals is applied to the V-band fluxes of OJ 287 from 1891 to 2010, 10 intrinsic mode functions with different timescales and a residual function are obtained from the light curve. The result shows that there exists a period of 12.34 yr in the V-band light variation of OJ 287, where the contribution rate of variance is maximal, and confirms that OJ 287 has a long-period variability in the V-band, and that the mean flux of OJ 287 tends to gradually decrease with time. 相似文献
14.
Jurkevich方法通常用来发现光变曲线的周期 ,并且根据V2 m 极小值的大小来验证所发现的光变周期可靠性。但是 ,这种验证方法又带有一定的不确定性 ,最佳的方法是把所发现的周期与观测光变曲线拟合 ,得出每一个周期的振幅 ,以振幅大小来验证所发现的光变周期的可靠性。将此方法用于OJ2 87的历史光变曲线 ,得到其最主要的周期为 11.9年 ,与其它结果相符合。 相似文献
15.
Karen M. Leighly 《Astrophysics and Space Science》2005,300(1-3):137-142
Significant (marginal) detections of periodic signals have been recently reported in 3 (4) Active Galactic Nuclei. Three of
the detections were obtained from long EUVE light curves of moderate-luminosity Seyfert galaxies; the fourth was discovered
in Chandra data from the low-luminosity Seyfert 1 galaxy NGC 4395. When compared with Cyg X-1, I find that the period is related
to the luminosity as P∝ L2/3 rather than the expected one-to-one relationship. This result might be explained if the QPO is associated with the inner
edge of the optically thick accretion disk, and the inner-edge radius depends on the source luminosity (or black hole mass).
A discussion of uncertainties in the period detection methodology is also discussed. 相似文献
16.
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. 相似文献
17.
Recent observations provide strong evidence for the BL Lac object OJ287 exhibiting a 11.6±0.5 yr periodicity with a double-peaked
maxima in its optical flux variations. Several models have been proposed for the optical behavior. The 2005 November outburst
in OJ287 gives us a surprising result since calculation based on the periodicity was predicting such an outburst in late 2006.
Here we suggest a new model, it can not only explain the optical quasi-periodic behavior, but also the radio flares behavior
which is and simultaneous with the optical flares. We propose that OJ287 is a binary pair of super-massive black holes, both
of them creating a jet. The quasi-periodic double peaks would be due to the relativistic beaming effect on the emission coming
from the double helix jets. We used “core flares” to explain the large lags between light curves at different frequencies,
and the assumption of two jets appear to be merged with each other partly in the radio frequency emitting regions provides
a viable interpretation that we can see only a broad maximum which contains two radio flares that we cannot distinguish. 相似文献
18.
Sun Yu-Tao Liu Jie-Ying Liu Jin-zhong Ai Yan-Li Zhou Ming Qiao Er-lin 《Chinese Astronomy and Astrophysics》2011,35(2):103
The research on quasar OJ 287 has lasted over 100 years. OJ 287 exhibits the phenomenon of periodic two-peak outbursts with the eruptive period of 12 years. Observations are rather well interpreted with the black hole binary model. In this model, the secondary black hole moves around the primary black hole and crashes against the accretion disk of the primary black hole, causing outbursts. This model reasonably explains the light curves of OJ 287 and correctly predicts the time of future outbursts. These indirectly justify the precessional effect of general relativity and the existence of gravitational waves. The massive black hole in the center of galaxy is an important kind of gravitational wave source. However, the number of the galaxies with precisely determined kinematical equations of inner components is quite small. The precise kinematic orbits of black holes are provided by the black hole binary model, so the radiation of gravitational waves can be studied on the basis of these kinematic orbits. Based on the existing work, the evolutionary relations of the radiation power and waveform of gravitational waves with time are first derived by using the post-Newtonian approximation method. According to the current progress of the detection equipment of gravitational waves, i.e., IPTA (International Pulsar Timing Array), the direct detection of gravitational waves from OJ 287 may be possible within the future decade. 相似文献
19.
Matteo Guainazzi 《Astrophysics and Space Science》2009,320(1-3):129-134
I briefly review in this paper the main observational properties of relativistically broadened X-ray spectral lines in Galactic Black Holes and Active Galactic Nuclei, and the (scanty) estimates of their frequency in the corresponding parent populations. The available measurements allow us to derive some constraints on the black hole spin and mass, and on the accretion disk geometry and illumination. 相似文献
20.
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. 相似文献