Core-dominance parameter and polarization for Fermi blazars

We study core-dominance parameter R and polarization for blazars detected by Fermi LAT. Our results are as follows. (i) The blazars detected by Fermi LAT have higher average R and polarizations than those not detected by Fermi LAT. (ii) Compared with BL Lacs, flat-spectrum radio quasars (FSRQs) have lower average R and the ratio of beamed luminosity to the unbeamed luminosity f. (iii) In the diagram of polarization-Doppler factor relations, FSRQs may have p=α+3 and BL Lacs for p=α+2. These results suggest that the high optical polarization is correlated to the beaming effect. High polarization and core-dominance parameters are significantly more common among the LAT sources. The difference in polarization and core-dominance parameters between FSRQs and BL Lacs are due to the difference in their beaming effects and jet model.     

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.     

A unifying view of the spectral energy distributions of blazars

We collect data at well-sampled frequencies from the radio to the γ-ray range for the following three complete samples of blazars: the Slew survey, the 1-Jy samples of BL Lacs and the 2-Jy sample of flat-spectrum radio-loud quasars (FSRQs). The fraction of objects detected in γ-rays ( E  ≳ 100 MeV) is ∼ 17, 26 and 40 per cent in the three samples respectively. Except for the Slew survey sample, γ-ray detected sources do not differ either from other sources in each sample, or from all the γ-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities or of the broad-band spectral indices (radio to optical and radio to X-ray). We compute average spectral energy distributions (SEDs) from radio to γ-rays for each complete sample and for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that (i) the first peak occurs in different frequency ranges for different samples/luminosity classes, with most luminous sources peaking at lower frequencies; (ii) the peak frequency of the γ-ray component correlates with the peak frequency of the lower energy one; (iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of sources and the systematic trends of the SEDs as a function of luminosity favour a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQs. The general implications of this unified scheme are discussed while a detailed theoretical analysis, based on fitting continuum models to the individual spectra of most γ-ray blazars, is presented in a separate paper.     

The optical spectral slope variability of 17 blazars

Many quasi-simultaneous optical observations of 17 blazars are obtained from previous papers published over the last 19 years in order to investigate the spectral slope variability and understand the radiation mechanism of blazars. The long-period dereddened optical spectral slopes are calculated. We analyse the average spectral slope distribution, which suggests that the spectra of flat spectrum radio quasars (FSRQs) and high energy peaked BL Lac objects (HBLs) are probably deformed by other emission components. The average spectral slopes of low energy peaked BL Lac objects(LBLs), which scatter around 1.5, show a good accordance with the synchrotron self-Compton (SSC) loss-dominated model. We present and discuss the variability between the spectral slope and optical luminosity. The spectra of all HBLs and LBLs get flatter when they turn brighter, while for FSRQs this trend does not exist or may even be reversed. This phenomenon may imply that there is a thermal contribution to the optical spectrum for FSRQs. For the FSRQ 1156+295, there is a hint that the slope gets flatter at both the brightest and faintest states. Our result shows that three subclasses locate in different regions in the pattern of slope variability indicator versus average spectral slope. The relativistic jet mechanism is supported by the significant correlation between the optical Doppler factor and the average spectral slope.     

Long-term optical-infrared color variability of blazars

The long-term optical and infrared color variability of blazars has been investigated with monitoring data from the Small and Moderate Aperture Research Telescope System(SMARTS). The sample in this study consists of 49 flat spectrum radio quasars(FSRQs) and 22 BL Lacertae objects(BL Lacs). The fractional variability amplitudes of each source have been calculated in both optical R band and infrared J band. Overall, the variability amplitudes of FSRQs are larger than those of BL Lacs. The results also suggest that the variability amplitude of most FSRQs is larger at a lower energy band(J band) than at a higher one(R band), but the variability amplitude of BL Lacs is larger at the higher energy band. Both types of blazars display color variation along with variability in brightness. However, they show different variation behaviors in general. In the whole data set, 35 FSRQs exhibit redder-whenbrighter trends, and 11 FSRQs exhibit opposite trends; 11 BL Lacs follow bluer-whenbrighter trends, and seven BL Lacs follow opposite trends. A detailed examination indicates that there are 10 blazars showing redder-when-brighter trends in their low state, and bluer-when-brighter or stable-when-brighter trends in their high state. Some more complicated color behaviors have also been detected in several blazars. The nonthermal jet emission and the thermal emission from the accretion disk are employed to explain the observed color behaviors.     

Blazars天体喷流光度和非成束光度的比值(英文)

根据聚束模型 ,利用 3 8个超光速射电源数据 ,估计他们的喷流光度和非成束光度的比值 .平均结果为     

Study of the relation between the jet and accretion-disk emission in Blazars using RATAN-600 multifrequency data

We study the correlation between the emission from the broad-line region (BLR) and the emission in other wavelength ranges (from radio to x-ray) for the sample of 37 blazars (25 flat-spectrum radio quasars (FSRQs) and 10 BLLac blazars). Studying the relation between luminosities in various wavebands and the BLR luminosity is an effective method to examine the connection between the accretion rate and the luminosity of the jet.We used simultaneous RATAN-600measurements of blazar flux densities at six frequencies: 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. The observational data from other bands was taken from the literature. To determine the effect produced by the state of the object on the correlation, for the radio data we used the measurements obtained with the RATAN-600 in two states-namely, the maximum and minimum flux density values.We show that at some frequencies of the radio band, there exists a correlation of emission with the emission in the BLR for two types of blazars. In the FSRQ and BL Lac blazars, the correlation between the flux from the BLR and the flux in the radio band is indistinguishable in all cases, except for the case when a strong flux density variation was considered for the BL Lac-type of blazars (tens of percent). At the same time, the levels of significance for BL Lac (at certain frequencies p is worse than 0.05) in the active state indicate only the probable presence of connection. On the example of the sample, we show that the variability of emission significantly affects the level of correlation. Our results are consistent with the theoretical predictions about the close relationship of the accretion disk and the jet in blazars.     

The broadband spectral energy distributions of SDSS blazars

We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broadband spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars(FSRQs) is larger than that of BL Lacertae(BL Lac) objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties,but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters.     

Characteristics of the Radiation from Blazars

We have collected short-timescale variability data of 47 blazars, estimated the masses of their central black holes and the sizes of their radiation regions at different wavebands, and made a statistical analysis on the calculated results. It is found that the central black hole mass of blazars falls in the range 10⁷M to 10¹⁰M, and that the BL Lac objects and the flat-spectrum radio quasars have very different central black hole masses (the latter being generally greater), while they have very similar sizes of radiation regions in the infrared and γ-ray wavebands. Also, using the collected bolometric luminosity data, we have analyzed the relationship between the bolometric luminosity of blazars and their short-timescale variability, and it is concluded that the radiations from the radio-selected BL Lac objects (RBLs) and flat-spectrum radio quasars (FSRQs) are strongly beam-confined, while the effect of relativistic beaming is relatively small for the X-ray-selected BL Lac objects (XBLs).     

Statistical Properties of a Blazar Sample and Comparison of HBLs, LBLs and FSRQs

Making use of the 2MASS Data Release, we have searched for near-infrared (JHK) counterparts to 268 blazars from Donato et al. and obtained 238 counterparts within 5" in the area covered by 2MASS. It provides us a sample with infrared data several times larger than the previous one of the same kind. Based on our sample and the sample by Donato et al., we have compared in detail the properties of HBLs, LBLs and FSRQs from five aspects and found that HBLs are significantly different from LBLs and FSRQs while LBLs are not obviously different from FSRQs. Our results strongly support the division of BL Lac objects into the high-frequency peaked (HBL) and low-frequency peaked (LBL) objects introduced by Padovani & Giommi and show that HBLs and LBLs are two kinds of blazar having different physical properties.     

耀变体亮温度与黑洞喷流能量的相关性讨论

耀变体(Blazars)的亮温度与黑洞喷流能量和吸积率有重要关系。搜集了53个耀变体源样本,包括22个蝎虎天体(BL Lacs)和31个平谱射电类星体(Flat Spectrum Radio Quasars,FSRQs),研究了耀变体亮温度与黑洞喷流能量的分布,并对子类中亮温度与黑洞喷流能量的相关性进行了讨论。研究结果表明:(1)蝎虎天体与平谱射电类星体的亮温度与黑洞喷流能量的分布存在明显差异,这可能与蝎虎天体与平谱射电类星体的内禀性质有关,也可能与其有无发射线及发射线的强弱有关;(2)蝎虎天体的亮温度与黑洞喷流能量之间的相关性较强,亮温度可以在一定程度上描述蝎虎天体的黑洞喷流能量,亮温度大的蝎虎天体喷流携带的能量也较大;(3)平谱射电类星体的亮温度与黑洞喷流能量之间有弱相关性,平谱射电类星体的亮温度不能清楚地描述黑洞喷流能量,黑洞喷流能量受亮温度影响较小,平谱射电类星体的黑洞喷流能量可能受到其他因素的影响;(4)耀变体的亮温度与黑洞吸积率之间有弱的相关性。     

Long-term optical color behavior of a sample of blazars

We report on the optical color variability of a sample of 24 blazars, consisting of nine flat spectrum radio quasars(FSRQs) and 15 BL Lacertae objects(BL Lacs), on timescales of years using simultaneous V-and R-band observations observed by the Kanata telescope at Higashi-Hiroshima Observatory.The correlations between color indices V-R and magnitudes reveal that 11 BL Lacs and one FSRQ exhibited significant(i.e., r 0.2 and P 0.01) bluer-when-brighter(BWB) trend and two FSRQs followed the redder-when-brighter(RWB) tend, indicating a possibility that the BWB chromatic trend is dominant for BL Lacs and the RWB trend is especially found in FSRQs, which has been presented occasionally in different samples of blazars.The superpositions of the red emission component from the Doppler-boosted relativistic jet and the blue component arising from the accretion disk might be a possible interpretation for the long-term color behaviors.     

Study on the Properties of Blazar Jets

The multi-wavelength quasi-simultaneous data of 55 Fermi blazars are fitted by using the conical jet model, and the physical properties of blazar jets are also investigated. Through the X²-minimization fitting procedure, the best-fit parameters of the conical jet model are obtained. Combined with the other parameters we collected, a statistical analysis is performed. The results of statistical analysis are summarized as follows: (1) The jet power obtained by the spectral energy distribution (SED) fitting is larger than the jet power calculated by using the extended radio luminosity; (2) There is no correlation between the Doppler factor 5 and the magnetic field strength B; (3) There is a correlation between the jet power and the accretion disk luminosity, and the Blandford-Znajek (BZ) mechanism can well explain the energy source of BL Lac jets rather than Flat Spectrum Radio Quasars (FSRQs); (4) The jet power is significantly correlated with the black hole mass.     

The evolutionary sequence of Fermi blazars

Using γ-ray data (α _γ , F _γ ) detected by Fermi Large Area Telescope (LAT) and black hole mass which has been compiled from literatures for 116 Fermi blazars, we calculated intrinsic γ-ray luminosity, intrinsic bolometric luminosity, intrinsic Eddington ratio and studied the relationships between all above parameters and redshift, between α _γ and L _γ . Furthermore, we obtained the histograms of key parameters. Our results are the following: (1) The main reason for the evolutionary sequence of three subclasses (HBLs, LBLs, FSRQs) may be Eddington ratio rather than black hole mass; (2) FSRQs occupy in the earlier, high-luminosity, high Eddington ratio, violent phase of the galactic evolution sequence, while BL Lac objects occur in the low luminosity, low Eddington ratio, late phase of the galactic evolution sequence; (3) These results imply that the evolutionary track of Fermi blazars is FSRQs ? LBLs ? HBLs.     

Gamma-ray luminosity function of gamma-ray bright AGNs

Detection of γ-ray emissions from a class of active galactic nuclei (viz blazars),has been one of the important findings from the Compton Gamma-Ray Observatory (CGRO). However, their-γ-ray luminosity function has not been well determined. Few at-tempts have been made in earlier works, where BL Lacs and Flat Spectrum Radio Quasars (FSRQs) have been considered as a single source class. In this paper, we investigated the evolution and γ-ray luminosity function of FSRQs and BL Lacs separately. Our investi-gation indicates no evolution for BL Lacs, however FSRQs show significant evolution. Pure luminosity evolution is assumed for FSRQs and exponential and power law evolu-tion models are examined. Due to the small number of sources, the low luminosity end index of the luminosity function for FSRQs is constrained with an upper limit. BL Lac lu-minosity function shows no signature of break. As a consistency check, the model source distributions derived from these luminosity functions show no significant departure from the observed source distributions.     

Spectral Variability of FSRQs

The optical variability of 29 flat spectrum radio quasars in SDSS Stripe 82 region are investigated by using DR7 released multi-epoch data. All FSRQs show variations with overall amplitude ranging from 0.24 mag to 3.46 mag in different sources. About half of FSRQs show a bluer-when-brighter trend, which is commonly observed for blazars. However, only one source shows a redder-when-brighter trend, which implies it is rare in FSRQs. In this source, the thermal emission may be responsible for the spectral behaviour.     

The relation between black hole masses and Lorentz factors of the jet components in blazars

We explore the relationship between black hole mass (MBH) and the motion of the jet components for a sample of blazars. The Very Long Baseline Array (VLBA) 2cm Survey and its continuation: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments (MOJAVE) have observed 278 radio-loud AGNs, of which 146 blazars have reliable measurements of their apparent velocities of the jet components. We calculate the minimal Lorentz factors for these sources from their measured apparent velocities, and their black hole masses ate estimated with their broad-line widths. A sig-nificant intrinsic correlation is found between black hole masses and the minimal Lorentz factors of the jet components. The Eddington ratio is only weakly correlated with the min-imal Lorentz factor, which may imply that the Blandford-Znajek (BZ) mechanism may dominate over the Blandford-Payne (BP) mechanism for the jet acceleration (at least) in blazars.     

The Correlation between γ-Ray and Radio Emissions for the Fermi Blazars

Based upon the Fermi blazars sample, the radio and γ-ray emissions are compiled for a sample of 74 γ-ray loud blazars to calculate the radio to γ-ray effective spectrum index α _{R γ}. The correlations between α _{R γ} and γ-ray luminosity, and between radio and γ-ray luminosity are also investigated.     

The relationship between the radio core dominance parameter and the spectral index in different classes of extragalactic radio sources

Active galactic nuclei(AGNs)have two major classes,namely radio loud AGNs and radio quiet AGNs.A small subset of the radio-loud AGNs is called blazars,which display extreme observational properties,such as rapid variability,high luminosity,high and variable polarization,and superluminal motion.All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight.Observations suggest that the orientation can be expressed by a core-dominance p...     

The dying accretion and jet in a powerful radio galaxy of Hercules A

Hercules A(Her A) is one of a rare class of dying and transition-type objects, which has a pair of giant, powerful radio lobes and a weak radio core. We reduce and analyze the radio data of Her A that were observed by the Expanded Very Large Array(EVLA) during 2010-2011 at C band. The intensity distribution is very smooth along the edge of the lobe front and the intensity also sharply decreases at the edge, which supports that magnetic fields may play an important role in radio lobes. The spectrum of the weak core is very steep and the core flux becomes weaker by about ten percent when compared to what was observed twenty years ago, which suggest that the central engine is still dying quickly. Her A deviates a lot from the relation between [O III] luminosity and low-frequency 178 MHz luminosity(LO III-L178 MHz) as defined by other FR I/II sources. However, when only radio core emission is considered, it roughly follows an LO III-L178 MHzcorrelation. This result supports that the black-hole accretion and large-scale jet in Her A did not evolve simultaneously, and indicates that although the large-scale jet is still powerful, the accretion and inner jet have changed into an inactive state. Based on the estimated Bondi accretion rate, we model the spectrum of Her A with a radiatively inefficient accretion flow and jet model.