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).     

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.     

A theoretical unifying scheme for gamma-ray bright blazars

The phenomenology of γ-ray bright blazars can be accounted for by a sequence in the source power and intensity of the diffuse radiation field surrounding the relativistic jet. Correspondingly, the equilibrium particle distribution peaks at different energies. This leads to a trend in the observed properties: an increase of the observed power corresponds to: (i) a decrease in the frequencies of the synchrotron and inverse Compton peaks, and (ii) an increase in the ratio of the powers of the high- and low-energy spectral components. Objects along this sequence would be observationally classified respectively as high-frequency BL Lac objects, low-frequency BL Lac objects, high-polarization quasars and low-polarization quasars.   The proposed scheme is based on the correlations among the physical parameters derived in the present paper by applying to 51 γ-ray loud blazars two of the most accepted scenarios for the broad-band emission of blazars, namely the synchrotron self-Compton and external Compton models. This also explains the observational trends presented by Fossati et al., dealing with the spectral energy distributions of all blazars. This gives us confidence that our scheme applies to all blazars as a class.     

The Deep X-Ray Radio Blazar Survey (DXRBS) – II. New identifications

We have searched the archived, pointed ROSAT Position Sensitive Proportional Counter data for blazars by correlating the WGACAT X-ray data base with several publicly available radio catalogues, restricting our candidate list to serendipitous X-ray sources with a flat radio spectrum ( α _r≤0.70, where S _ν ∝ ν ^{− α} ). This makes up the Deep X-ray Radio Blazar Survey (DXRBS). Here we present new identifications and spectra for 106 sources, including 86 radio-loud quasars, 11 BL Lacertae objects, and nine narrow-line radio galaxies. Together with our previously published objects and already-known sources, our sample now contains 298 identified objects: 234 radio-loud quasars [181 flat-spectrum quasars: FSRQ ( α _r≤0.50) and 53 steep-spectrum quasars: SSRQ], 36 BL Lacs and 28 narrow-line radio galaxies. Redshift information is available for 96 per cent of these. Thus our selection technique is ∼90 per cent efficient at finding radio-loud quasars and BL Lacs. Reaching 5-GHz radio fluxes ∼50 mJy and 0.1–2.0 keV X-ray fluxes a few ×10⁻¹⁴ erg cm⁻² s⁻¹, DXRBS is the faintest and largest flat-spectrum radio sample with nearly complete (∼85 per cent) identification. We review the properties of the DXRBS blazar sample, including redshift distribution and coverage of the X-ray-radio–power plane for quasars and BL Lacs. Additionally, we touch upon the expanded multiwavelength view of blazars provided by DXRBS. By sampling for the first time the faint end of the radio and X-ray luminosity functions, this sample will allow us to investigate the blazar phenomenon and the validity of unified schemes down to relatively low powers.     

Gamma-Ray and VLBI Radio Emission from Gamma-ray-loud Blazars

Based on the γ-ray data of 51 γ-ray-loud blazars in the third EGRET catalog and VLBI radio data at 2.29 GHz in high state. we studied the correlations between the VLBI and γ-rayluminosities and the fluxes using the partial correlation analysis method. The results show that there is a strong correlation between γ-ray and VLBI radio fluxes and a significant correlation between γ-ray and VLBI radio luminosities. These results are likely to provide a possible support for self-Compton model of the γ-ray emission in blazars. It also shows that the γ-ray radiation may come from the region within the order of 1 pc which is consistent with the results given by luminosity variation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The blazar sequence: validity and predictions

The “blazar sequence” posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively small synchrotron peak frequencies, ν _peak, and that the least powerful such objects should have the highest ν _peak values. This would have strong implications for our understanding of jet formation and physics and the possible detection of powerful, moderately high-redshift TeV blazars. I review the validity of the blazar sequence by using the results of very recent surveys and compare its detailed predictions against observational data. I find that the blazar sequence in its simplest form is ruled out. However, powerful flat-spectrum radio quasars appear not to reach the ν _peak typical of BL Lacs. This could indeed be related to some sort of sequence, although it cannot be excluded that it is instead due to a selection effect.      

The contribution of unresolved radio-loud AGN to the extragalactic diffuse gamma-ray background

We present a calculation of the blazar contribution to the extragalactic diffuse γ -ray background (EGRB) in the EGRET energy range. Our model is based on inverse-Compton scattering as the dominant γ -ray production process in the jets of flat spectrum radio quasars (FSRQs) and BL Lac objects, and on the unification scheme of radio-loud AGN. According to this picture, blazars represent the beamed fraction of the Fanaroff–Riley radio galaxies (FR galaxies).
The observed log  N –log  S distribution and redshift distribution of both FSRQs and BL Lacs constrain our model. Depending slightly on the evolutionary behaviour of blazars, we find that unresolved AGN underproduce the intensity of the extragalactic background radiation. With our model only 20–40 per cent of the extragalactic background emission can be explained by unresolved blazars if we integrate to a maximum redshift of Z _max=3. For Z _max=5, blazars could account for 40–80 per cent of the EGRB. Roughly 70–90 per cent of the AGN contribution to the EGRB would result from BL Lacs. While the systematic uncertainties in our estimate for the FSRQ contribution appear small, in the case of BL Lacs our model parameters are not consistent with the results from studies in other wavelength regimes, and therefore may have larger systematic uncertainties. Thus we end up with two possibilities, depending on whether we underpredict or overpredict the BL Lac contribution: either unresolved AGN cannot account for the entire EGRB, or unresolved BL Lacs produce the observed background.
We predict a significant flattening of the γ -ray log  N –log  S function in the next two decades of flux below the EGRET threshold.     

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.     

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。     

Intermediate BL Lac objects

The 200-mJy sample, defined by Marchã et al., contains about 60 nearby, northern, flat-spectrum radio sources. In particular, the sample has proved effective at finding nearby radio-selected BL Lac objects with radio luminosities comparable to those of X-ray-selected objects, and low-luminosity flat-spectrum weak emission-line radio galaxies (WLRGs). The 200-mJy sample contains 23 BL Lac objects (including 6 BL Lac candidates) and 19 WLRGs. We will refer to these subsamples as the 200-mJy BL Lac sample and the 200-mJy WLRG sample, respectively. We have started a systematic analysis of the morphological pc-scale properties of the 200-mJy radio sources using VLBI observations.
This paper presents VLBI observations at 5 and 1.6 GHz of 14 BL Lac objects and WLRGs selected from the 200-mJy sample. The pc-scale morphology of these objects is briefly discussed. We derive the radio beaming parameters of the 200-mJy BL Lac objects and WLRGs and compare them with those of other BL Lac samples and with a sample of FR I radio galaxies. The overall broad-band radio, optical and X-ray properties of the 200-mJy BL Lac sample are discussed and compared with those of other BL Lac samples, radio- and X-ray-selected. We find that the 200-mJy BL Lac objects fill the gap between HBL and LBL objects in the colour–colour plot, and have intermediate α _XOX as expected in the spectral energy distribution unification scenario. Finally, we briefly discuss the role of the WLRGs.     

Host galaxies and the unification of radio-loud AGN

Our HST WFPC2 survey of 110 BL Lac objects, from six complete X-ray-, radio-, and optically-selected catalogs, probes the host galaxies of low-luminosity radio sources in the redshift range 0<z<1.35. The host galaxies are luminous ellipticals, well matched in radio power and galaxy magnitude to FR I radio galaxies. Similarly, the host galaxies of high luminosity quasars occupy the same region of this plane as FR II radio galaxies (matched in redshift). This strongly supports the unification of radio-loud AGN, and suggests that studying blazars at high redshift is a proxy for investigating less luminous (to us) but intrinsically identical radio galaxies, which are harder to find at high z. Accordingly, the difference between low-power jets in BL Lac objects and high-power jets in quasars can then be related to the FR I/FR II dichotomy; and the evolution of blazar host galaxies or their nuclei (jets) should correspond to the evolution of radio galaxies.     

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。     

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.     

Spectral Energy Distribution for Some Fermi Blazarstwo

The observational data from radio to X-ray wavebands were collected from the SSDC (Italian Space Agency Science Data Center) for 68 Fermi blazars, and their spectral energy distributions (SEDs) were calculated by means of the least square fitting with a log-parabolic function. Based on the SED fitting parameters, the correlations of the synchrotron peak frequency, curvature and effective spectral index were discussed, and an empirical formula was also proposed to estimate the synchrotron peak frequencies by using the effective spectral indexes. The main results are as follows: (1) From the linear correlation between the synchrotron peak frequency (lg ν_p) and the curvature (k), we find that the result supports the energy-dependent acceleration probability model for all BL Lac objects, while the result for the BL Lac objects of lg ν_p > 15.3 is consistent with the model of fluctuation of fractional acceleration gain. (2) For the sources of nearly same lg ν_p, a significant correlation between the effective spectral index α_ro of the radio-optical waveband and the curvature is detected, while the effective spectral index α_ox of the optical-x-ray waveband is not correlated with the curvature. According to the effective spectral index α_ro, a relation between the synchrotron peak frequency and the curvature can be defined.     

The estimations of four basic parameters for gamma-ray loud blazars

The method used in our previous papers is adopted to estimate four basic pa-rameters (the central black hole mass (M), the boosting factor (or Doppler factor) (δ), the (d)) for 59 γ-ray loud blazars (20 BL Lacertae objects and 39 fiat spectrum radio quasars).The central black hole masses estimated for this sample are in a range of from 107 M⊙to 109 M⊙. In the case of black hole mass, there is no clear difference between BL Lacertae objects and flat spectrum radio quasars, which is consistent with the previous results sug-gesting that the central black hole masses do not play an important role in the evolutionary sequence of blazars.     

A Study of the γ-ray and X-ray Radiations of BL Lac Objects

The X-ray and γ-ray flux densities of 18 γ-loud BL Lac objects as well as their average spectral indices of X-ray wave band (1 keV) and γ-ray wave band (>100 MeV) are collected, and the correlations among the various quantities are examined. The results indicate: (1) The X-ray flux density and the γ-ray flux density exhibit rather strong correlations in all the states, high, low or mediate. (2) Between the mean spectral indices in X-ray and γ-ray wave bands there is a comparatively intense anti-correlation. (3) Between the average spectral indices and the X-ray and γ- flux densities there is no evident correlation either in the high or the mediate state. (4) Between the average spectral index of γ-ray wave band and the flux density of X-rays in low state there is a rather strong anticorrelation. Between the mean spectral index of X-ray wave band and the γ-flux density in low state there also exists a weak correlation. The results of our analysis support the viewpoint that both the X-ray and γ-ray emissions of BL Lac objects come from the synchrotron radiation and synchrotron self Compton (SSC) radiation with one and the same distribution of relativistic electrons.     

Correlation between X-ray and γ-ray for Fermi blazars

Using γ-ray band data detected by Fermi Large Area Telescope (LAT) and X-ray band data for 78 blazars, we find a medium correlation between X-ray flux and γ-ray flux in all states. A medium correlation is also found between X-ray (1 keV) mean spectral index α _x and γ-ray mean spectral index α _γ for BL Lacertae objects (BL Lacs), and there is no correlation for Flat Spectrum Radio Quasars (FSRQs). From these results, we suggest that the most likely radiation mechanism for the high energy gamma-rays would be synchrotron self-Compton (SSC), and that the gamma-ray emission mechanism may be somewhat different for BL Lacs and FSRQs.     

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.     

A Statistical Study of XBLs, RBLs and FSRQs at 1.5 GHz

BL Lac objects are similar to the fiat spectrum radio quasars in many aspects except regarding the emission lines.In order to study their relationship,we selected 56 BL Lacertae objects(33 X-ray-selected,23 radio-selected)and 45 flat spectrum radio quasars,analyzed their radio luminosities and core-dominance parameters.We found that the radio luminosities of the radio selected BL Lac objects located in between the X-ray selected BL Lac objects and the fiat spectrum radio quasars.However,this intermediate position does not bold for the core-dominance parameter:the RBLs have the largest core-dominance parameters.This sug- gests that the core-dominance parameter can not be taken as a sequencing criterion.We also investigated the correlation between the luminosity and the core-dominance parameter for the three subclasses.We concluded that,here,the sequence XBL-RBL—FSRQ still exists.     

The CLASS blazar survey – II. Optical properties

This paper presents the optical properties of the objects selected in the CLASS blazar survey. Because an optical spectrum is now available for 70 per cent of the 325 sources present in the sample, a spectral classification, based on the appearance of the emission/absorption lines, is possible. A wide variety of optical spectral types is found. Besides 'classical' BL Lacs (42), BL Lac candidates (5) and high-power     flat spectrum radio quasars (67), a significant number of 'passive' elliptical galaxies (41) is also found. Moreover, 33 broad emission line objects with a low radio power     are discovered, suggesting that at least a fraction (∼     per cent) of low-power blazars have a broad line region. Finally, 34 objects showing only narrow emission lines, either as a result of some starburst activity in the host galaxy or as a result of the presence of an active galactic nucleus, appear in the sample.