A Research on the Characteristics of Light Variation of Blazar 3C 273 in 2-10 keV

From the original observed data of RXTE (Rossi X-ray timing explorer), the data of 3C 273 in the X-ray band of 2-10 keV from February 2, 1996 (MJD 50115) to August 27, 2007 (MJD 54339) are analyzed. The photon spectral indexes and corresponding fluxes of the observational data from 1010 observations are obtained in total. The average time of each observation is 1666.76 seconds. By analyzing the spectral variation and behavior of the light variation of 3C 273 in the hard X-ray band of 2-10 keV during observational periods, it is found that there was a significant anti-correlation between the photon spectral index Γ and flux lgF_{2∼10 keV} in February 2000, March and April 2003, February, March and July 2004, as well as 2006 and 2007. During the observational periods in 1999 and from 2000 to 2007, there was also a significant anti-correlation between the monthly average behaviors of Γ and lgF_{2∼10 keV}. From the quantitative analysis of the behavior of light variation in the entire observational period, several relatively large light variations are found. The evidence of the existence of the Fe emission line with average width of 93.85±21.49 eV is also found by fitting a part of the spectra. Through analyzing the intensity of the light variation and features of Fe emission line, it is found that 3C 273 has some characteristics of blazars and Seyfert galaxies simultaneously.     

Spectral variability in hard X-rays and the evidence for a 13.5 years period in the bright quasar 3C273

We report the observation of nearest quasar 3C273 made with LASE instrument on November 20th, 1998 as a part of our continuing programme of balloon borne hard X-ray observations in the 20–200 keV band using high sensitivity Large Area Scintillation counter Experiment. Our data clearly show a steep spectrum in the 20–200 keV with power law spectral indexα = 2.26 ± 0.07. This is in complete contrast to the reported data from OSSE and BeppoSAX which suggest the value of 1.3 to 1.6 for the power law index in the X-ray energy band, but is quite consistent with the value derived for the high energy gamma ray data. A single power law fit in the X-ray and gamma ray energy bands points to a common origin of these photons and the absence of spectral break around 1 MeV as suggested in literature. We have reanalyzed the available data to study the temporal variability of the spectrum in the hard X-ray band. Our analysis reveals that 50 keV flux from the source, shows a strong modulation with a period of about 13.5 years. The analysis of the optical light curve of the source also supports the 5000 day period. We discuss the emission mechanism and the possible sites for X-ray photons along with the implications of the long term periodicity with respect to source geometry.     

Constraints on a soft X-ray excess in the quasar 3C 279

We present the results of a three-week daily monitoring campaign of the quasar 3C 279 by the X-ray satellites RXTE ROSAT . A cross-correlation provides no evidence for any time lag between the very similar soft and hard X-ray light curves, and the source shows no significant spectral variability over the observing period. There is no evidence to support the presence of a soft excess, with a 99 per cent upper limit on any such component of 25 per cent of the total observed luminosity in the 0.1–2 keV band (<3 × 10³⁸ W). This fraction (but not the luminosity) is significantly lower than that of the soft excess observed in 3C 273.     

Multiwavelength XMM–Newton observations of the Laor et al. sample of PG quasars

We present XMM–Newton /EPIC spectra for the Laor et al. sample of Palomar Green (PG) quasars. We find that a power law provides a reasonable fit to the 2–5 keV region of the spectra. Excess soft X-ray emission below 2 keV is present for all objects, with the exception of those known to contain a warm absorber. However, a single power law is a poor fit to the 0.3–10.0 keV spectrum and instead we find that a simple model, consisting of a broken power law (plus an iron line), provides a reasonable fit in most cases. The equivalent width of the emission line is constrained in just 12 objects but with low (<2σ) significance in most cases. For the sources whose spectra are well fitted by the broken-power-law model, we find that various optical and X-ray line and continuum parameters are well correlated; in particular, the power-law photon index is well correlated with the FWHM of the Hβ line and the photon indices of the low- and high-energy components of the broken power law are well correlated with each other. These results suggest that the 0.3–10 keV X-ray emission shares a common (presumably non-thermal) origin, as opposed to suggestions that the soft excess is directly produced by thermal disc emission or via an additional spectral component. We present XMM–Newton Optical Monitor (OM) data, which we combine with the X-ray spectra so as to produce broad-band spectral energy distributions (SEDs), free from uncertainties due to long-term variability in non-simultaneous data. Fitting these optical–UV spectra with a Comptonized disc model indicates that the soft X-ray excess is independent of the accretion disc, confirming our interpretation of the tight correlation between the hard and soft X-ray spectra.     

Comparison and Analysis of the Light Variations of 3C 273, 3C 279 and 3C 345

The blazar 3C 345 is quite similar to the γ-ray blazar 3C 279 in respect of redshift, spectral energy distribution from the radio to the X-ray wave band, and so on. However, it was not detected by EGRET. We compared the differences and similarities between 3C 345 and the γ-ray sources 3C 279 and 3C 273 in respect of variation amplitudes (in the 8 GHz, 22 GHz, 37 GHz and B band), the smallest variation time scales in the optical and the time lags between different bands to search possible reason for the lack of the γ-ray radiation in 3C 345. From our analyses it is found that the variation amplitudes in the radio band for 3C 345 and 3C 279 are quite similar; the variation amplitudes in the optical wave band gradually decrease in the order 3C 279, 3C 345 and 3C 273, and variations on the order of days are found in these three sources. It is also found that the time lag in 3C 345 is much longer than that in 3C 279 and is approximately the same as that in 3C 273. Based on the similarity of other observational properties between 3C 345 and 3C 273, such as the presence of the big blue bump and their comparable infrared luminosities, it is proposed that the spectral energy distribution and the luminosity in the γ-ray band for 3C 345 are similar to those for 3C 273. It is indicated by our simple calculations that if 3C 273 has a similar redshift to that of 3C 345, then even at the burst state, EGRET could not detect any radiations from 3C 273. This might be the reason why 3C 345 had never been detected by EGRET.     

Diagnostics of the Low-Cutoff Energy of Nonthermal Electrons in Solar Microwave and Hard X-Ray Bursts

The low-cutoff energy has a strong effect on the relationship between the radiation and electron spectral indices in both nonthermal gyrosynchrotron and bremsstrahlung theories. Hence, we have to calculate or fit the low-cutoff energy together with the electron spectral index as two independent parameters. Theoretical calculations of nonthermal gyrosynchrotron and bremsstrahlung radiations suggest a new method to obtain the exact solutions of the low-cutoff energy and the electron spectral index from the observable photon spectral indices at two adjacent energy or frequency bands (double power law). One flare on 10 June 2000 was studied as an example of the hard X-ray and microwave diagnostics for the low-cutoff energy and the electron spectral index. The results showed some differences between hard X-ray and microwave diagnostics.     

Chaotic Feature in the Light Curve of 3C 273

Some nonlinear dynamical techniques, including state-space reconstruction and correlation integral, are used to analyze the light curve of 3C 273. The result is compared with a chaotic model. The similarities between them suggest there is a low-dimension chaotic attractor in the light curve of 3C 273.     

ASCA and ROSAT observations of the Seyfert 1 galaxy RX J0437.4−4711

Results of ASCA and ROSAT observations of the Seyfert 1 galaxy RX J0437.4−4711 are presented. The X-ray continuum spectrum can be described by the sum of a power law with photon index 2.15 ± 0.04 and a soft emission component characterized by a blackbody with temperature 29 ± 2 eV. The total luminosity of the soft component is larger than that of the power-law component if the power law is cut off around a few hundred keV. A weak absorption edge with τ = 0.26 ± 0.13 at the rest-frame energy of E  = 0.83 ± 0.05 keV and an Fe Kα line with EW = 430 ± 220 eV at an energy E  = 6.47 ± 0.15 keV are also detected. The X-ray flux showed a 47 per cent increase between two ASCA observations 4 months apart, but no spectral variability was seen. We argue that reprocessing of the hard X-ray emission cannot produce all the soft X-ray emission, since the total luminosity of the soft component is larger than that of the integrated power-law component. Similarities with some stellar black hole candidates are briefly discussed.     

Spectral analysis of Swift long gamma-ray bursts with known redshift

We study the spectral and energetics properties of 47 long-duration gamma-ray bursts (GRBs) with known redshift, all of them detected by the Swift satellite. Due to the narrow energy range (15–150 keV) of the Swift -BAT detector, the spectral fitting is reliable only for fitting models with two or three parameters. As high uncertainty and correlation among the errors is expected, a careful analysis of the errors is necessary. We fit both the power law (PL, two parameters) and cut-off power law (CPL, three parameters) models to the time-integrated spectra of the 47 bursts, and we present the corresponding parameters, their uncertainties and the correlations among the uncertainties. The CPL model is reliable only for 29 bursts for which we estimate the  ν f _ν  peak energy E _pk. For these GRBs, we calculate the energy fluence and the rest-frame isotropic-equivalent radiated energy,   E _γ,iso  , as well as the propagated uncertainties and correlations among them. We explore the distribution of our homogeneous sample of GRBs on the rest-frame diagram   E '_pk  versus   E _γ,iso  . We confirm a significant correlation between these two quantities (the 'Amati' relation) and we verify that, within the uncertainty limits, no outliers are present. We also fit the spectra to a Band model with the high-energy PL index frozen to −2.3, obtaining a rather good agreement with the 'Amati' relation of non- Swift GRBs.     

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…     

Ten Years of Monitoring 3C 273 with XMM–Newton

We present ten years optical/UV/X-ray observations of 3C 273 performed using XMM–Newton between 2000 and 2009. The short-time scale variability behaviour of the soft and hard X-ray light curves may suggest different origins of the soft/hard X-ray emissions. We fit well the 0.2–10 keV X-ray spectrum with a hard power-law component plus a soft Comptonization component. The lack of Γ???F correlation of the hard power-law component and the weakness of iron K _α lines may support dominance of the jet component. The soft X-ray excess correlates much better with ultraviolet than with the hard power-law component, strongly suggesting that soft excess emission originates from inverse Comptonization of UV photons.     

Accretion disc variability in the hard state of black hole X-ray binaries

XMM–Newton X-ray spectra of the hard state black hole X-ray binaries (BHXRBs) SWIFT J1753.5−0127 and GX 339−4 show evidence for accretion disc blackbody emission, in addition to hard power laws. The soft and hard band power spectral densities (PSDs) of these sources demonstrate variability over a wide range of time-scales. However, on time-scales of tens of seconds, corresponding to the putative low-frequency Lorentzian in the PSD, there is additional power in the soft band. To interpret this behaviour, we introduce a new spectral analysis technique, the 'covariance spectrum', to disentangle the contribution of the X-ray spectral components to variations on different time-scales. We use this technique to show that the disc blackbody component varies on all time-scales, but varies more, relative to the power law, on longer time-scales. This behaviour explains the additional long-term variability seen in the soft band. Comparison of the blackbody and iron line normalizations seen in the covariance spectra in GX 339−4 implies that the short-term blackbody variations are driven by thermal reprocessing of the power-law continuum absorbed by the disc. However, since the amplitude of variable reflection is the same on long and short time-scales, we rule out reprocessing as the cause of the enhanced disc variability on long time-scales. Therefore, we conclude that the long time-scale blackbody variations are caused by instabilities in the disc itself, in contrast to the stable discs seen in BHXRB soft states. Our results provide the first observational evidence that the low-frequency Lorentzian feature present in the PSD is produced by the accretion disc.     

The origin of the strong soft excess and puzzling iron line complex in Mkn 841

Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM‐Newton for a total cumulated exposure time of ∼108 ks. We present in this paper a broad band spectral analysis of the complete EPIC‐pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5–2 keV soft X‐ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on different timescales. The broad‐band 0.5–10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self‐consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Time Lags between the 22 and 37 GHz Bursts of 48 Radio-loud AGNs

Based on the light curves at 22 and 37 GHz from the Metsahovi monitoring pro-gram, we investigate the time lags between the two radio bands for 48 radio-loud AGNs. DCF and ZDCF analyses are applied to the data. Our results show that there is a strong correlation between the two radio frequencies for all the sources, with the variations in the light curvesat 37 GHz leading the ones at 22 GHz in general. There is no obvious differences between different sub-class AGNs as regards the time lag. In two sources, it was found that the bursts at the lower frequency lead the ones at the higher frequency. One possible explanation is that electron acceleration dominates the light curve until the radiation reaches the maximum. Some sources, such as 3C 273, 3C 279, 3C 345 and 3C 454.3, have good enough data, so we can calculate their lags burst-by-burst. Our calculations show that different outbursts have dif- ferent lags. Some bursts have positive lags, most of bursts have no clear lags, and a few have negative lags. This result means that different bursts are triggered by different mechanisms, and the interpretation for the result involves both an intrinsic and a geometric mechanism. The positive lags are well consistent with the shock model, and we use these lags to calculate the typical magnetic field strength of the radiating region.     

Properties of the continua of eight PG QSOs from ASCA data

We have analyzed the continua of eight PG QSOs, obtained by the ASCA SIS detector with a higher energy resolution and a broader band than by ROSAT/PSPC and attempted to fit the data with a single power law, a double power law and a truncated power law. Four of the objects exhibit soft X excess in 0.4 – 10 keV. They are Mkn 478, PG 1444+407, PG 1543+48 and 3C 273. Furthermore, the ratio of the excess to total flux is the smaller, the greater the optical luminosity is. The presence or otherwise of the soft X-ray excess is unrelated to the radio properties and luminosity of the object.     

Luminosity function of high-mass X-ray binaries and anisotropy in the distribution of active galactic nuclei toward the Large Magellanic Cloud

In 2003?C2012, the INTEGRAL observatory has performed long-term observations of the Large Magellanic Cloud (LMC). At present, this is one of the deepest hard X-ray (20?C60 keV) surveys of extragalactic fields in which more than 20 sources of different natures have been detected. We present the results of a statistical analysis of the population of high-mass X-ray binaries in the LMC and active galactic nuclei (AGNs) observed in its direction. The hard X-ray luminosity function of high-mass X-ray binaries is shown to be described by a power law with a slope ?? 1.8, that in agreement with the luminosity function measurements both in the LMC itself, but made in the soft X-ray energy band, and in other galaxies. At the same time, the number of detected AGNs toward the LMC turns out to be considerably smaller than the number of AGNs registered in other directions, in particular, toward the source 3C 273. The latter points to the nonuniformity of the distribution of matter in the local Universe.     

Low frequency quasi-periodic oscillations in the hard x-ray emission from cygnus x-1

The observations of the black hole binary Cygnus X-l were made in the energy band of 20–100keV with a balloon-borne Xenon-filled multiwire proportional counter telescope on 5th April 1992. Timing analysis of the data revealed the presence of Quasi-Periodic Oscillations (QPO) in the hard X-ray emission from the source. The QPO feature in the power density spectrum is broad with a peak at a frequency of 0.06 Hz. This result is compared with similar reports of QPOs in Cyg X-l in soft and hard X-rays. Short time scale random intensity variations in the X-ray light curve are described with a shot noise model.     

X-ray spectral complexity in narrow-line Seyfert 1 galaxies

We present a systematic analysis of the X-ray spectral properties of a sample of 22 'narrow-line' Seyfert 1 galaxies for which data are available from the ASCA public archive. Many of these sources, which were selected on the basis of their relatively narrow H β linewidth (FWHM ≤2000 km s⁻¹), show significant spectral complexity in the X-ray band. Their measured hard power-law continua have photon indices spanning the range 1.6–2.5 with a mean of 2.1, which is only slightly steeper than the norm for 'broad-line' Seyfert 1s. All but four of the sources exhibit a soft excess, which can be modelled as blackbody emission ( T _bb≈100–300 eV) superposed on the underlying power law. This soft component is often so strong that, even in the relatively hard bandpass of ASCA , it contains a significant fraction, if not the bulk, of the X-ray luminosity, apparently ruling out models in which the soft excess is produced entirely through reprocessing of the hard continuum.
Most notably, six of the 22 objects show evidence for a broad absorption feature centred in the energy range 1.1–1.4 keV , which could be the signature of resonance absorption in highly ionized material. A further three sources exhibit 'warm absorption' edges in the 0.7–0.9 keV bandpass. Remarkably, all nine 'absorbed' sources have H β linewidths below 1000 km s⁻¹, which is less than the median value for the sample taken as a whole. This tendency for very narrow linewidths to correlate with the presence of ionized absorption features in the soft X-ray spectra of NLS1s, if confirmed in larger samples, may provide a further clue in the puzzle of active galactic nuclei.     

基于EMD-AR谱的3C 273光变周期分析

光变是Blazar最显著的观测特征之一,有的光变呈准周期性. Blazar周期光变可能为其中心黑洞和吸积盘等内部物理结构提供重要信息.因此,周期分析对于讨论Blazar的光变有重要意义.结合经验模态分解(Empirical Mode Decomposition, EMD)和自回归(Auto-regressive, AR)模型谱估计方法的优点,提出了一种基于EMD-AR谱的组合光变周期分析新方法.先对观测数据进行EMD分解,得到各阶模态分量,并计算其与原始光变曲线的相关系数,再取相关度高的分量求和后估算AR谱,最后将此功率谱的周期分析方法用于天体的光变数据分析.讨论了EMD-AR谱方法的原理和应用步骤,并用此方法对类星体3C 273在1887—2016年的观测数据进行了分析,得到3C 273的长时标周期分别为:21.23、13.51、11.02、5.51、4.69、3.79、2.76 yr,与文献中常用方法的分析结果有很好的一致性;短时标周期分别为:(30±1)、(15±0.3)、(7.5±0.2)、(10±0.1)、(5±0.6)、(6±0.4)和(3±0.5) min,此结果未见相关...