Methods for the Quasi-Periodic Variability Analysis in Blazars

In this work, four methods are introduced to analyse the unevenly sampled data. The four methods are power spectral density, auto-correlation function, structure function and Jurkevich method. Some interesting mathematical links are derived amongst the four methods. These links show that the four methods have the same performance. For the Jurkevich method, the effect of the width of bins is apparent. If the width is half the time scale, the method has better performance.     

Flare Characteristics from X-ray Light Curves

A new methodology is given to determine basic parameters of flares from their X-ray light curves. Algorithms are developed from the analysis of small X-ray flares occurring during the deep solar minimum of 2009, between Solar Cycles 23 and 24, observed by the Polish Solar Photometer in X-rays (SphinX) on the Complex Orbital Observations Near-Earth of Activity of the Sun-Photon (CORONAS-Photon) spacecraft. One is a semi-automatic flare detection procedure that gives start, peak, and end times for single (“elementary”) flare events under the assumption that the light curve is a simple convolution of a Gaussian and exponential decay functions. More complex flares with multiple peaks can generally be described by a sum of such elementary flares. Flare time profiles in the two energy ranges of SphinX (1.16?–?1.51 keV, 1.51?–?15 keV) are used to derive temperature and emission measure as a function of time during each flare. The result is a comprehensive catalogue – the SphinX Flare Catalogue – which contains 1600 flares or flare-like events and is made available for general use. The methods described here can be applied to observations made by Geosynchronous Operational Environmental Satellites (GOES), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and other broad-band spectrometers.     

Stochastic Resonance of Accretion Disk and the Persistent Low-Frequency Quasi-Periodic Oscillations in Black Hole X-ray Binaries

In this paper, we use a Langevin type equation with a damping term and stochastic force to describe the stochastic oscillations on the vertical direction of the accretion disk around a black hole, and calculate the luminosity and power spectral density (PSD) for an oscillating disk. Then we discuss the stochastic resonance (SR) phenomenon in PSD curves for different parameter values of viscosity coefficient, accretion rate, mass of black hole and outer radius of the disk. The results show that our simulated PSD curves of luminosity for disk oscillation have the same profile as the observed PSD of black hole X-ray binaries (BHXBs) in the lowhard state, and the SR of accretion disk oscillation may be an alternative interpretation of the persistent low-frequency quasi-periodic oscillations (LFQPOs).     

Autoregressive Spectral Estimation for Quasi-Periodic Oscillations

Modern methods of spectral estimation based on parametric time-series models are useful tools in power spectral analysis. We apply the autoregressive (AR) model to study quasi-periodic oscillations (QPOs). An empirical formula to estimate the expectation and standard deviation of the noise AR power densities is derived, which can be used to estimate the statistical significance of an apparent QPO peak in an AR spectrum. An iterative adding-noise algorithm in AR spectral analysis is proposed and applied to studying QPOs in the X-ray binary Cir X-1.     

新近对耀变体(Blazar)的X射线观测

本文综述了ASCA ,RXTE ,BeppoSAX和XMM -NEWTON对TeV耀变体 (Blazar)X射线研究的最新进展。主要集中在X射线资料的时间和光谱分析的最重要的方面 ,包括功率谱密度 ,结构函数 ,带间时间延迟 ,同步峰值能量的漂移和谱演化。对这些新结果的物理意义也进行了简要讨论。     

X-ray Time Lags in TeV Blazars

We use Monte Carlo/Fokker?CPlanck simulations to study the X-ray time lags. Our results show that soft lags will be observed as long as the decay of the flare is dominated by radiative cooling, even when acceleration and cooling time scales are similar. Hard lags can be produced in the presence of a competitive achromatic particle energy loss mechanism if the acceleration process operates on a time scale such that particles are slowly moved towards higher energy while the flare evolves. In this type of scenario, the ??-ray/X-ray quadratic relation is also reproduced.     

Blazar 的X射线谱性质

从Donato文献中选择了一个含有69个Blazar的样本，样本中每个源有多个X射线辐射流量数据，用该样本研究了流量密度和谱指数之间的关系，以及研究了三类源（HBL，LBL，FSRQ）的红移和谱指数的分布。结果表明：对于HBLs，谱指数和流量密度之间有一个较好的反相关关系存在，而对于LBLs和FSRQs却没有相关。因此认为HBL的X射线是同步辐射所致，而LBL和FSRQ的X射线辐射较为复杂可能是同步自康普顿过程导致。HBL显示软X射线谱，而FSRQ显示硬X射线谱，LBL居中。在谱图中HBL位于近端，rSRQ位于远端，LBL居中。     

Low-Frequency Quasi-Periodic Oscillations in the X-ray Nova MAXI J1535-571 at the Initial Stage of Its 2017 Outburst

We report the discovery of low-frequency quasi-periodic oscillations (QPOs) in the power spectrum of the X-ray nova MAXI J1535-571 at the initial stage of its outburst in September 2017. Based on data from the SWIFT and INTEGRAL instruments, we have traced the evolution of the QPO parameters (primarily their frequency) with time and their correlation with changes in the X-ray spectrum of the source (changes in the emission flux and hardness). We place constraints on the theoretical QPO generation models.     

UV and X-ray Variability of Blazars

It is well established that the blazars show flux variations in the complete electromagnetic (EM) spectrum on all possible time scales ranging from a few tens of minutes to several years. Here we report the review of various UV and X-ray flux variability properties of blazars. Our analysis show that UV variability amplitude is smaller than X-rays, mostly soft X-rays hardness ratio show correlations with blazar luminosity and different modes of variability might be operating for different time scales and epochs. Quasi periodic oscillations are seen on a few occasions in blazars, higher fraction of high energy peaked blazars show intra day and short term variabilities in X-rays but variability duty cycle is much less in optical bands on intra day time scale compared to low energy peaked blazars. But these results are yet to be established.     

Observational Studies of the X-Ray Quasi-Periodic Oscillations of a Solar Flare

We study an M2.6 flare observed with RHESSI on 22 August 2005. The light curves of the hard X-rays (counts and photon fluxes), the derived number fluxes, as well as the energy fluxes of energetic electrons all presented a damped quasi-periodic oscillation. The modulation depth of the hard X-rays increased with the energies. For the energy fluxes of energetic electrons, the modulation depth can be as high as 90%. During the oscillations, however, the plasma temperature had no apparent change. No correspondence was found between the motions of the flare loops and the quasi-periodic oscillations. We conclude that an oscillation with a high modulation depth for a period of about four minutes cannot be easily explained with the existing mechanisms.     

Peculiar Emission Line Generation from Ultra-Rapid Quasi-Periodic Oscillations of Exotic Astronomical Objects

The purpose of this article is to alert astronomers, particularly those using spectroscopic surveys, to the fact that exotic astronomical objects (e.g. quasars or active galactic nuclei) that send ultra-rapid quasi periodic pulses of optical light would generate spectroscopic features that look like emission lines. This gives a simple technique to find quasi periodic pulses separated by times smaller than a nanosecond. One should look for emission lines that cannot be identified with known spectral lines in spectra. Such signals, generated by slower pulses, could also be found in the far infra-red, millimeter and radio regions, where they could be detected as objects unusually bright in a single narrow-band filter or channel. The outstanding interest of the technique comes from its simplicity so that it can be used to find ultra-rapid quasi-periodic oscillators in large astronomical surveys. A very small fraction of objects presently identified as Lyman \(\alpha \) emitters that do not have other spectral features to confirm the Lyman \(\alpha \) redshift, may possibly be quasi-periodic oscillators. However this is only a hypothesis that needs more observations for confirmation.     

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.     

Variability of Soft X—ray Spectral Shape in Blazars Observed by ROSAT

1 INTRODUCTION Blazars, including BL Lac objects, highly polarized and optically violently variable quasars,and flat-spectrum radio quasars (FSRQs), are characterized by highly variable non-thermalemission which dominates their characteristics from radio to y-ray bands. The mechanismbelieved to be responsible for their broadband emission is synchrotron radiation followed by in-verse Compton (IC) scattering at higher energies (e.g. Blandford & Konigl 1979). Relativisticbeaming of a jet…     

Separation of Different Contributions to the Total X-ray Luminosity in Gamma-ray Loud Blazars

The relativistic beaming model has been successfully used to explain many of the observational properties of active galactic nuclei. In this model the total emission is formed by two components, one beamed, one unbeamed. However, the exact contribution from each component in unresolved sources is still not clear. In the radio band, the core and extended emissions are clearly separated. We adopt the method proposed by Kembhavi to separate the two contributions in the X-ray emissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that the beamed emission dominates the X-ray flux and the unbeamed X-ray emission is correlated with the extended radio emission of the considered objects. We also find that the ratio of the beamed to the unbeamed X-ray luminosity is correlated with the X-ray spectral index, an effect that should be a consequence of the underlying X-ray emission mechanism.     

低质量X射线双星的毫秒级准周期信号——最近的进展

最近对低质量X射线双星中的千赫兹准周期振动的研究表明 ,是辐射压力 ,而不是盘和磁球的相互作用以及处于盘内边界的广义相对论效应在短时标的盘切断机制上起作用。本文给出了一些研究结果及讨论。     

On the Light Curves of GRB Afterglows

We present gamma-ray burst afterglow light curves in X-ray, optical and radio bands for various distributions of accelerated electrons behind the shock. The effects of lateral expansion of the jet and of winds in typical Wolf-Rayet star on the evolution are discussed. The light curves in the radiative case decline more rapidly than those in the adiabatic case. Under the combined effect of jet expansion and wind environment, the light curves have the greatest deviation from those of the standard model. All these results refer to the relativistic phase.     

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.     

A Study on the Light Curves of GRBs

It is generally believed that the complexity and variability of the light curves of gamma-ray bursts (GRBs) are caused by the internal shocks, which would occur when a rapid shell catches up a slower one and collides with it. The electrons in the shock layer are heated by the shocks and radiate via the mechanisms of synchrotron radiation and inverse Compton scattering. Based on relativistic kinematics, a relation between the photon number of the emission from the rapidly moving shock layer and the number of the photons received by an observer is derived. Then, employing the angular spreading of the internal shock emission, the curve equation and profile of a single pulse are obtained, and the shape is typically in the shape of a fast rise and exponential decline. Furthermore, by using the model of the successive collisions of multiple shells under the condition of reasonable parameters, the observed light curves are fitted with a rather good effect. Therefore, by this means, more different types of light curves of GRBs can be explained.     

Microvariability in Blazars

Optically violent variable quasars and BL Lac objects, which form a subclass of active galactic nuclei are termed as Blazars. Blazars show high degree variation in their flux and polarization in a relatively shorter period of time. They are strong radio sources with a non-stellar continuum. Most of the BL Lac objects do not show any emission lines though in some cases very weak lines are observed. They harbour in elliptical galaxies. Some BL Lacs show superluminal motion indicating the flow of matter at relativistic speeds close to the line of sight. It is likely that the enormous energy produced by these objects may be due to a massive black hole with an accretion disc system. Some Blazars have been observed to detect short time variations in their flux and polarization in the visual band. These studies are aimed at understanding the physical processes taking place in the central engine. Detecting shorter period variations assumes significance as they impose restrictions on the total volume from where the huge amount of energy is comming out. To date the recorded shortest period variation in visual band is 6.3 min in OJ 287, a BL Lac object. Attempts are being made to detect shorter period variations, which pose observational challenges. It is generally accepted that the central engine of AGN harbours a massive blackhole with an accretion disc surrounding it. This revised version was published online in July 2006 with corrections to the Cover Date.     

On Methods for the Light Curves Extrema Determination

We present two methods for the determination of moments of extrema and their errors appropriate for the analysis of light variations of variable objects. The method I is suitable for determination of times of extrema of non-periodical variables or objects, whose light curves vary. The method II is apt for O-C analyses of objects whose light curves are more or less repeating. Both methods are displayed on the analysis of BL Cam light variations and compared with the Kwee-van Woerden method.