• Volume 32, Issue 1-2

March 2011,   pages  1-357

• Praface

• Radio Band Observations of Blazar Variability

The properties of blazar variability in the radio band are studied using the unique combination of temporal resolution from single dish monitoring and spatial resolution from VLBA imaging. Such measurements now available in all four Stokes parameters, together with theoretical simulations, identify the origin of radio band variability and probe the characteristics of the radio jet where the broadband blazar emission originates. Outbursts in total flux density and linear polarization in the optical-to-radio bands are attributed to shocks propagating within the jet spine, in part, based on limited modelling invoking transverse shocks; new radiative transfer simulations allowing for shocks at arbitrary angle to the flow direction confirm this picture by reproducing the observed centimeter-band variations observed more generally, and are of current interest since these shocks may play a role in the 𝛾-ray flaring detected by Fermi. Recent UMRAO multifrequency Stokes V studies of bright blazars identify the spectral variability properties of circular polarization for the first time and demonstrate that polarity flips are relatively common. All-Stokes data are consistent with the production of circular polarization by linear-to-circular mode conversion in a region that is at least partially selfabsorbed. Detailed analysis of single-epoch, multifrequency, all-Stokes VLBA observations of 3C 279 support this physical picture and are best explained by emission from an electron-proton plasma.

• Intra-Day Variability of Sagittarius A* at Multi-Wavelengths

This paper reviews the recent progress in the study of the intra-day variability (IDV) of Sagittarius A* (Sgr A*), the best known supermassive black hole candidates with a dark mass concentration of 4 × 106 𝑀 at the center of our galaxy.

• Models for High-Energy Radiation from Blazars

We discuss on the modelling of blazar jets as emitters of multiwavelength radiation with the implementation of a lepto-hadronic treatment. Assuming that injection of non-thermal electrons and protons can take place at the base of the jet, the stationary particle distributions can be found using an inhomogeneous one-dimensional transport equation with cooling and convection. The goal of this approach is to replace the widely used one-zone purely leptonic approximation by a more realistic model. We argue that the rapid variability observed in emission from blazars can be obtained as a result of interaction of the jet with obstacles, i.e., molecular clouds and stars. Long term variability is likely related to changes in the injection and physical conditions in the acceleration region.

• Peculiar Physical Properties of HST-1 in M87

We report on VLA observations of HST-1 in M87 at 8 GHz from 2003–2007, during which a long major outburst occurs from radio to X-ray wave bands. At the VLA resolution, the flux density of HST-1 rises rapidly from 2003, peaks at the end of 2004, and then falls slowly in subsequent stages, which is similar to that in optical and X-ray wave bands. It appears that HST-1 moves with an apparent speed of 1.23𝑐 ± 0.91𝑐, and the fractional polarization keeps rising through the whole major outburst. The persistent increase in polarization level may mainly be attributed to the formation of a couple of new subcomponents’ of relatively high degree of polarization within HST-1, and the weakening depolarization due to Faraday rotation and/or opacity through the whole major outburst.

• Radio Variability of First 3-Month Fermi Blazars at 5 GHz: Affected by Interstellar Scintillation?

Blazars from the first-three-months Fermi-AGN list were observed with the Urumqi 25-m radio telescope at 5 GHz in IDV (Intra-Day Variability) mode and inter-month observation mode. A significant correlation between the flux density at 5 GHz and the 𝛾-ray intensity for the Fermi-LAT detected blazars is seen. There is a higher IDV detection rate in Fermi detected blazars than those reported for other samples. Stronger variability appears at lower galactic latitudes; IDV appears to be stronger in weaker sources, indicating that the variability is affected by interstellar scintillation.

• X-ray Cavities in Galaxy Groups and Clusters: Central Gas Entropy Excess as Direct Evidence for AGN Feedback

Observations of X-ray jets and cavities in clusters of galaxies observed by Chandra are briefly reviewed. A recent study on the excess of central gas entropy, which can be considered as direct evidence for AGN feedback in galaxy groups and clusters is presented. An expanded account of this study has been presented in RAA (Wang et al. 2010).

• Multi-Wavelength Studies on H2O Maser Host Galaxies

H2O maser emissions have been found in external galaxies for more than 30 years. Main sciences associated with extragalactic H2O masers can be summarized roughly into three parts: maser emission itself, AGN sciences and cosmology exploration. Our work in this field focusses on two projects: X-ray data analysis of individual maser source using X-ray penetrability to explore maser host obscured AGN; multi-wavelength statistical properties of the whole published H2O maser sample. Here their nuclear radio properties were investigated in detail, based on their 6-cm and 20-cm radio observation data. Comparing the radio properties between maser-detected sources and non-detected sources at similar distance scale, we find that: (1) maser host galaxies tend to have higher nuclear radio luminosity; (2) the spectral index of both samples is comparable (∼ 0.6), within the error ranges. In addition, for AGN-maser sources, the isotropic maser luminosity tends to increase with rising radio luminosity. Thus we propose the nuclear radio luminosity as one good indicator for searching AGN-masers in the future.

• Long-term Periodicity Analysis of Polarization Variation for Radio Sources

We use the database of University of Michigan Radio Astronomy Observatory (UMRAO) at three radio bands (4.8, 8 and 14.5 GHz) to analyse the long-term polarization variation in search of the possible periodicity. Using the power spectral analysis method (PSA), the Jurkevich method and the discrete correlation function (DCF) method, we find that there are 16 sources lying in periodicity. The results show the astrophysically meaningful periodicity covering 2.1 years to 16.2 years at 4.8 GHz, 2.8 years to 16.3 years at 8 GHz, and 1.8 years to 16.6 years at 14.5 GHz.

• Radio Observation of the 11-Month Fermi-AGN at Urumqi Observatory

We carry out flux observation at 5 GHz for 124 sources from the ‘clean’ sample of Fermi catalog 1LAC (The First LAT AGN Catalog) with Urumqi 25 m telescope. We find that it is obvious that there is a correlation between the 𝛾-ray and the radio flux density for blazars. For the subclasses, the correlation for FSRQs is strong, but the correlation for BL Lacs is weak.

• The Eddington Ratio of H2O Maser Host AGN

The Eddington ratio 𝜆 was derived for the entire maser host AGN sample, based on the intrinsic X-ray luminosity, the X-ray bolometric correction 𝐶X and the mass of central black hole. Further the [O III] bolometric correction 𝐶[O III] was estimated for our sample. Possible relations were also investigated between the maser luminosity and the bolometric luminosity – the Eddington ratio.

• A Visual Method of Time Scale Determination using a PC for Radio Sources

Variability is one of the extremely observational properties. In the radio bands, variability is caused by the shock in the jet. In this case, emissions increase rapidly following an exponential curve, and then decrease rapidly also in an exponential curve. The variability time scale is important with regard to the physics carrying on in the jet. However, it is not easy to fit the light curve. In this paper, we proposed a method of light curve fitting on a PC machine, in which the theoretical exponential light curve is adopted to the observations using the least regression method. Using this method, anybody can fit the light curve and get the time scale by moving and clicking themouse.We also used this method to some light curves obtained from the archive and compared our results with those in the literature.

• Radio Observations of the S5 Sample

The S5 sample was monitored on a monthly basis since December 2008 at Urumqi Observatory. Most of the sources are variables and a considerable proportion (about 20%) exhibited a significant inter-month flux variability (modulation index &gt; 4%) during the 1-year observation.

• IDV Observations of BL0716+714 at 5 GHz

A selected sample of intra-day variable AGN had been observed for 3–4 days per month at the Urumqi Observatory. The sample includes 7 target sources and 7 calibrators. The BL Lac object B0716+714 shows prominent intraday and long term variations.

• The Relationship between Radio Luminosity and Core-Dominance Parameter for XBLs

In this work, we investigate the correlation between the luminosity and the core-dominance parameter for a sample of X-ray selected BL Lacertae objects (XBLs), and found that the extended luminosity is strongly anti-correlated with the core-dominance parameter while the core (or the total) luminosity is not correlated with the core-dominance parameter. If this is the case, then we can expect that the lower extended luminosity XBLs and their core luminosity is relatively higher. This can be explained by a relativistic beaming model since in this case, the viewing angle is smaller and the emissions dominate the extended emissions. Therefore, the anti-correlation is in fact the result of the relativistic beaming model.

• Position Measurements of the Core in 3C 66B

It was argued that 3C 66B, a nearby radio galaxy, harbors a supermassive black hole binary (SMBHB). To investigate this, a 4-epoch VLBA phase referencing imaging observation was performed in 2004–2005. Here we present some preliminary results of this project. We found a large position difference compared to previous results.

• Variability of Blazars

Variability is one of the characteristics of blazars. The rapid variability is superposed on the long term variation. In this work, the variability on different time scales, such as intra-day (IDV), short-term (STV) and long-term (LTV) variations are presented for some sources. We also presented our own observations of some selected objects, for which the historical data were compiled for periodicity analysis using several methods. The parameters of the binary black hole system OJ 287 are determined.

• Blazar Observations in Infrared and Optical Regions: Magnetic Field Strength Evaluation

A brief review of the methods to evaluate the strength of magnetic fields in blazars on some examples using observational data is presented.

• 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, autocorrelation 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.

• 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.

• Astronomical Plate Archives and Binary Blazars Studies

There are about 3 million astronomical photographic plates around the globe, representing an important data source for various aspects of astrophysics. The main advantage is the large time coverage of 100 years or even more. Recent digitization efforts, together with the development of dedicated software, enables for the first time, effective data mining and data analyses by powerful computers with these archives. Examples of blazars proposed and/or investigated on the astronomical plates are presented and discussed.

• The Optical Microvariability and Spectral Changes of the BL Lacertae Object S5 0716+714

The BL Lac object S5 0716+714 was monitored in the optical band during October 2008, December 2008 and February 2009. We achieved a best temporal resolution of about 5 min in the 𝐵𝑉𝑅𝐼 bands. The source was active during the whole monitoring campaign. It showed microvariability in 13 days out of 14 days of observation. Four fast flares were observed with amplitudes ranging from 0.3–0.75 mag. The overall amplitude changes during the whole campaign are 𝛥 𝐵 ∼ 0.𝑚 89, 𝛥 𝑉 ∼ 0.𝑚 80, 𝛥 𝑅 ∼ 0.𝑚 73, and 𝛥 𝐼 ∼ 0.𝑚 51. On internight time scales, strong bluer-when-brighter chromatism was found while different spectral behaviours were found on intranight time scales.

• Optical Photometric and Radio Monitoring of Gamma-ray Loud Blazars

We present the results of multi-years optical and radio monitoring of radio-loud quasars 0716+714 and 1633+382, aimed at searching the flux variations and possible correlation at different wave bands. Our radio observations were performed with a 22-m radio telescope of the Crimean Astrophysical Observatory, 14-m radio telescope of the Metsahovi Radio Observatory and 26-m telescope of the Michigan Radio Astronomy Observatory at 4.8, 8.0, 14.5, 22.2 and 36.8 GHz. The optical observations were performed with a Zeiss-1000 reflector of the Special Astrophysical Observatory in the B, V, R filters.

The harmonic analysis performed for the light curves of 0716+714 from 2002–2010 in radio and optical wave bands revealed the presence of an apparent periodical component in the flux variations. The period of the radio light curve is nearly 3.6 years, and coincides within the errors with the period of the optical light curve (nearly 3.4 years). The duration of the flares is approximately the same in radio and optical ranges, and it is about 100–150 days.

• Optical Spectra Evolution of BL Lac Objects

Many quasi-simultaneous optical observations of nine BL Lac objects are obtained from literature. We study the relationship between the optical spectral index and the luminosity of BL Lac objects, and are tempted to exploit spectral evolution in the optical frequency ranges. Our results show that:

1. The optical spectra index of the low-frequency peaked BL Lac objects (LBLs) is steeper than the high-frequency peaked BL Lac objects (HBLs);

2. The spectra tend to be softer when the source becomes brighter for LBLs and the intermediate BL Lac objects (IBLs) (i.e., bluer-when-brighter), and the spectra of HBLs does not vary when the brightness of HBLs changes. Possible explanations are briefly discussed for this phenomenon.

• Multi-Band Spectral Properties of Fermi Blazars

The multi-band data covering optical, X-ray and 𝛾-ray energy regions of 130 Fermi blazars in the First LAT AGN Catalog (1LAC) were collected to investigate the broadband spectral properties. The composite spectral indices show that HBLs have convex optical-to-X-ray continua and concave X-ray-to-𝛾-ray continua, 𝛼𝛾 𝑋𝛾 &gt; 0 and 𝛼𝑋𝑂𝑋 &lt; 0, while FSRQs and LBLs have 𝛼𝛾 𝑋𝛾 &lt; 0. The 𝛼𝑋𝑂𝑋 distribution of FSRQs and LBLs extends from negative to positive values. We suggest 𝛼𝛾 𝑋𝛾 &gt; 0 and 𝛼𝑋𝑂𝑋 &lt; 0 could be considered as a criterion for HBLs. Moreover, HBLs have narrow distribution of peak interval of log $v^{\text{ic}}_{\text{p}}=\log v^{\text{syn}}_{\text{p}}$, and FSRQs have significant anti-correlation between log $v^{\text{ic}}_{\text{p}}-\log v^{\text{syn}}_{\text{p}}$ and $\log v^{\text{syn}}_{\text{p}}$. This indicates that SSC model is responsible for high energy emission of HBLs, while EC for FSRQs. Our results also indicate that FSRQs with larger break energy of electrons have smaller bulk Lorentz factor of dissipation region.

• Re-Analysis of QPO in 3C 273 Light Curve

We have developed analysis tools to search for quasi periodic oscillations in light curves from active galactic nuclei, using the following time series techniques: Wavelets, periodogram, Lomb–Scargle periodogram, structure function and multi-harmonic analysis of variance.

The analysis tools incorporate different noise models with significant levels for all the techniques that is an improvement over the previous work. By looking for consistently high significance, we make the detection of periodicities more robust. We apply this tool to a previously reported QPO (Espaillat et al. 2008) in the X-ray light curve of 3C 273 with a periodicity of ∼ 3300 s and find that the significance is only 74% in the wavelet and fails to show up above 95% significance in the periodogram and multi-harmonic analysis of variance.

• Novel Algorithms for Astronomical Plate Analyses

Powerful computers and dedicated software allow effective data mining and scientific analyses in astronomical plate archives. We give and discuss examples of newly developed algorithms for astronomical plate analyses, e.g., searches for optical transients, as well as for major spectral and brightness changes.

• The Spectral Index and Beaming Effect for Radio Sources

In this paper, we revisited the relationship between the spectral index and the core-dominance parameter using a larger sample of blazars. Conclusively, we explain that the spectral index is associated with the core-dominance parameter using the two-component relativistic beaming model.

• Optical Monitoring of 3C 66A in 1994–2008

3C 66A is one of the most interesting blazar. Our monitoring was carried out with a 1.56-m telescope of the Shanghai Astronomical Observatory (SHAO) from 13 December 1994 to 9 November 2008. Some peaks and gradual brightening of the source up to three times were observed.

• Long-Term Optical Spectra Variability of BL Lacertae Object S5 0716+714

Based on the long-term data from observations, we present an evidence for its spectral index variability behaviour in optical bands for BL Lacertae object S5 0716+714.We find that the spectral index variability period is in agreement with the flux variability period of about 1180 days in optical bands.We also find that the spectral index variability has periods of about 71 and 60 days which cannot be compared with the amplitude of long-term variability.

• Gamma-Ray and Multiwavelength Emission from Blazars

Blazars are now well understood as approaching relativistic jets aligned with the line of sight. The long-time uncertainty about the demographics of blazars is starting to become clearer: since the Fermi blazar sample includes a larger fraction of high-frequency peaked blazars (like the typical X-ray-selected blazars in, say, the Einstein Slew Survey sample) than did the higher-flux-limit EGRET blazar sample, these low-luminosity sources must be more common than their higher luminosity, low-frequency-peaked cousins. Blazar spectral energy distributions have a characteristic two-component form, with synchrotron radiation at radio through optical (UV, X-ray) frequencies and gamma-rays from X-ray through GeV (TeV) energies.Multiwavelength monitoring has suggested that gamma-ray flares can result from acceleration of electrons at shocks in the jet, and there appears to be an association between the creation of outflowing superluminal radio components in VLBI maps and the gamma-ray flares. In many cases, the gamma-ray emission is produced by inverse Compton upscattering of ambient optical-UV photons, although the contribution from energetic hadrons cannot be ruled out. The next few years of coordinated gamma-ray, X-ray, UV, optical, infrared and radio monitoring of blazars will be important for characterizing jet content, structure, and total power.

• Quasi-Periodic Oscillations in the X-ray Light Curves of Blazars

Any quasi-periodic variations discovered in blazar light curves would contain important information on the location and nature of the processes within the emission regions. In non-blazar active galactic nuclei, particularly Seyfert galaxies, any such fluctuations are very likely to be associated with the accretion disks, but in blazars they would almost certainly have to emanate from jets. This brief review summarizes recent claims for the presence of quasi-periodic variability in the X-ray emission of several AGN, focusing on blazars. Although no individual claim of the presence of a QPO in AGN X-ray light curves is absolutely convincing, there are some good cases for the presence of QPOs, including the Narrow Line Seyfert 1 galaxy, RE J1034+396, the quasar, 3C 273 and the BL Lac, PKS 2155−304.

• 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.

• Spectral Evolution of Synchrotron and Inverse Compton Emission in BL Lac Objects

With XMM–Newton observations, the X-ray spectral variations and the derived physical implications for two very high energy gamma-ray BL Lac objects PKS 2155–304 and S5 0716+714 are presented.

• Fermi-LAT View of Bright Flaring Gamma-Ray Blazars

The Fermi LAT provides a continuous and uniform monitoring of the Universe in the gamma-ray band. During the first year many gamma-ray blazar flares, some unidentified transients and emission by the Sun while in a quiet state were promptly detected. This is mainly due to the design of the mission, featuring a detector, the LAT with a wide field of view, and to the operation of the spacecraft itself, that can cover every region of the sky every 3 hours. Nevertheless, the scientific exploitation of this monitoring is more fruitful when early information about transients reaches a broader community. In this respect, the indefatigable activity of flare advocates, who worked on weekly shifts to validate the results and quickly broadcast information about flares and new detections, was the key to most scientific results.

• 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 𝐾𝛼 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.

• Chandra and XMM–Newton Observations of H2O Maser Galaxy Mrk 266

For H2O megamaser galaxy Mrk 266, its Chandra and XMM–Newton data are analyzed here. It shows existence of two obscured nuclei (separation is ∼ 5''). Our preferred model, the high energy reflected model can fit the hard component of both nuclei spectra well.

• X-ray Time Lags in TeV Blazars

We use Monte Carlo/Fokker–Planck 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 𝛾-ray/X-ray quadratic relation is also reproduced.

• Modelling the IDV Emissions of the BL Lac Objects with a Langevin Type Stochastic Differential Equation

In this paper, we introduce a simplified model for explaining the observations of optical intra-day variability (IDV) of the BL Lac Objects. We assume that the source of the IDV are the stochastic oscillations of an accretion disk around a supermassive black hole. The stochastic fluctuations on the vertical direction of the accretion disk are described by using a Langevin type equation with a damping term and a random, white noise type force. Furthermore, preliminary numerical simulation results are presented, which are based on the numerical analysis of the Langevin stochastic differential equation.

• X-ray Radiation Mechanisms and the Beaming Effect of Hot Spots and Knots in AGN Jets

The observed broadband spectral energy distributions (SEDs) of 22 hot spots and 45 knots are modelled with single-zone lepton models. Considering the sources at rest, the X-rays of some hot spots can be explained by the SSC model with magnetic field being consistent with the equipartition magnetic field in magnitude of order 1, but at the same time an unreasonably low magnetic field is required to model the X-rays for all knots. When considering the relativistic bulk motion of the sources, the IC/CMB model well explains the X-ray emission for most of them under the equipartition condition. We show that the ratio of observational luminosity 𝑅𝐿 is tentatively correlated with the co-moving equipartition magnetic field 𝐵'eq and the beaming factor 𝛿. These facts suggest that the observational differences of the X-rays from the knots and hot spots may be mainly due to the differences in the Doppler boosting effect and the co-moving magnetic field of the two kinds of source.

• The Tilt between Acretion Disk and Stellar Disk

The orientations of the accretion disk of active galactic nuclei (AGN) and the stellar disk of its host galaxy are both determined by the angular momentum of their forming gas, but on very different physical environments and spatial scales. Here we show the evidence that the orientation of the stellar disk is correlated with the accretion disk by comparing the inclinations of the stellar disks of a large sample of Type 2 AGNs selected from Sloan Digital Sky Survey (SDSS, York et al. 2000) to a control galaxy sample. Given that the Type 2 AGN fraction is in the range of 70–90 percent for low luminosity AGNs as a priori, we find that the mean tilt between the accretion disk and stellar disk is ∼ 30 degrees (Shen et al. 2010).

• 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 𝛼R𝛾 . The correlations between 𝛼R𝛾 and 𝛾-ray luminosity, and between radio and 𝛾-ray luminosity are also investigated.

• Estimating Black Hole Masses of Blazars

Estimating black hole masses of blazars is still a big challenge. Because of the contamination of jets, using the previously suggested size–continuum luminosity relation can overestimate the broad line region (BLR) size and black hole mass for radio-loud AGNs, including blazars. We propose a new relation between the BLR size and 𝐻𝛽 emission line luminosity and present evidences for using it to get more accurate black hole masses of radio-loud AGNs. For extremely radio-loud AGNs such as blazars with weak/absent emission lines, we suggest the use of fundamental plane relation of their elliptical host galaxies to estimate the central velocity dispersions and black hole masses, if their velocity dispersions are not known but the host galaxies can be mapped. The black hole masses of some well-known blazars, such as OJ 287, AO 0235+164 and 3C 66B are obtained using these two methods and the 𝑀–𝜎 relation. The implications of their black hole masses on other related studies are also discussed.

• Variability of Spectral Energy Distribution of Blazar S5 0716+714

The emission from blazars is known to be variable at all wavelengths. The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra of emitting electrons and/or the physical parameters of the jet. Meaningful modeling of blazar broadband spectra is required to understand the extreme conditions within the emission region. Not only is the broadband SED crucial, but also information about its variability is needed to understand how the highest states of emission occur and how they differ from the low states. This may help in discriminating between models. Here we present the results of our SED modeling of the blazar S5 0716+714 during various phases of its activity. The SEDs are classified into different bins depending on the optical brightness state of the source.

• Unification of Radio Galaxies and their Accretion Jet Properties

We investigate the relation between black hole mass, 𝑀bh, and jet power, 𝑄jet, for a sample of BL Lacs and radio quasars. We find that BL Lacs are separated from radio quasars by the FR I/II dividing line in 𝑀bh-𝑄jet plane, which strongly supports the unification scheme of FR I/BL Lac and FR II/radio quasar. The Eddington ratio distribution of BL Lacs and radio quasars exhibits a bimodal nature with a rough division at 𝐿bol/𝐿Edd ∼ 0.01, which imply that they may have different accretion modes. We calculate the jet power extracted from advection-dominated accretion flow (ADAF), and find that it requires dimensionless angular momentum of black hole 𝑗 ≃ 0.9 - 0.99 to reproduce the dividing line between FR I/II or BL Lac/radio quasar if dimensionless accretion rate $\dot{m} = 0.01$ is adopted, which is required by the above bimodal distribution of Eddington ratios. Our results suggest that black holes in radio galaxies are rapidly spinning.

• Period of Light Variability in BL Lac ON 231

In this paper, the authors have compiled the data of about 100 years in B-band of the BL Lac ON 231 and used this database to analyze periodicity signals in the optical light curve. Two different methods were applied: the wavelet analysis and the Discrete Correlation Function (DCF) method. We revealed the existence of periods of 13.5 years in the source variability.

• Multi-Waveband Emission Maps of Blazars

We are leading a comprehensive multi-waveband monitoring program of 34 𝛾-ray bright blazars designed to locate the emission regions of blazars from radio to 𝛾-ray frequencies. The maps’ are anchored by sequences of images in both total and polarized intensity obtained with the VLBA at an angular resolution of ∼ 0.1 milliarcseconds. The time-variable linear polarization at radio to optical wavelengths and radio to 𝛾-ray light curves allow us to specify the locations of flares relative to bright stationary features seen in the images and to infer the geometry of the magnetic field in different regions of the jet. Our data reveal that some flares occur simultaneously at different wavebands and others are only seen at some of the frequencies. The flares are often triggered by a superluminal knot passing through the stationary core’ on the VLBA images. Other flares occur upstream or even parsecs downstream of the core.

• Multi-Frequency Observations of Gamma-Ray Blazar 1633+382

We perform monthly monitoring of the quasar 1633+382 (4C+38.41) within a sample of 𝛾-ray blazars with the VLBA at 43 GHz along with optical photometric and polarimetric observations. We construct the 𝛾-ray light curve of 1633+382 using data obtained by the Fermi LAT. We find that a high 𝛾-ray state of the quasar starting in 2009 September is simultaneous with an increase of the flux in the mm-wave VLBI core. We resolve a superluminal feature on the VLBA images that appears to be responsible for the mm-wave flux increase. We find a strong correlation between optical and 𝛾-ray light curves with a delay of 𝛾-ray variations of 5 ± 3 days, as well as a strong correlation between optical flux and degree of polarization during the high 𝛾-ray state. Comparison between the optical polarization position angle and that in the VLBI core supports the idea that in the quasar 1633+382 a high 𝛾-ray state is connected with processes originating near the mm-VLBI core.

• Fundamental Plane of FSRQs from SDSS DR5 Quasar Catalogue

In this work, we explore a sample of 362 flat-spectrum radio quasars (FSRQs) to investigate the jet formation. We find that the fundamental plane for our FSRQs can be expressed as 𝐿5\;GHz ∝ 𝑀$^{-0.19}_{\text{bh}}$ 𝐿$^{1.08}_{\text{2\; keV}}$. We also find that the 5 GHz luminosities are tightly related to both black hole mass and Eddington ratio, which is established as 𝐿5\;GHz ∝ 𝑀$^{0.67}_{\text{bh}}$ (𝐿bol/𝐿EDD)1.32.

• On the Superluminal Motion of Radio-Loud AGNs

Apparent superluminal motion of different radio-loud AGNs are similarly related with beaming effect. The cosmological expanding effect would play no part in the superluminal motion of radio galaxies, BL Lacertae objects as well as quasars.Meanwhile, we confirm that estimates for apparent velocity 𝛽app and Doppler boosting factor 𝛿 based on multi-wavelength combination and variability are comparable.

• Variability of Fe II in Two NLS1s, PG 1700+815 and NGC 4051

We analyze the spectral variability for two narrow line Seyfert 1 galaxies, PG 1700+518 and NGC 4051 using the spectral decomposition method. We focus on their optical Fe II variability to investigate the origin of Fe II in AGNs. For PG 1700+518, we find that the Fe II size is about 200 light-days, which is consistent with the H𝛽 size derived from the empirical R–L relation. For NGC 4051, the [O III] 5007 Å flux is strongly correlated with continuum flux, suggesting that we should recalibrate the spectral flux on a scale defined by [O III] flux. The corrected light curves of Fe II, H𝛽, He II, 𝑓𝜆 (5100 Å) are given here. A detailed analysis will be given in the near future.

• Curvature Effect and the Spectral Softening Phenomenon Detected in GRB Afterglows

Detection of radiation from a relativistic fireball would be affected by the so-called curvature effect. I illustrate the expected temporal and spectral behaviours of this effect and show that it can well explain the observed spectral softening in the early GRB afterglows.

• Pumping Mechanisms for SiO Masers around VX Sgr

VX Sgr, a semi-regular variable, is a red giant star with intense SiO maser emission at 43 GHz. The pumping mechanism of the circumstellar SiO masers has been controversial for decades since its discovery. In order to pursue this long-standing problem further, we have carried out simultaneous VLBA observations of two 7 mm SiO masers at five epochs in about two years. We present relatively aligned 𝑣 = 1 and 𝑣 = 2, 𝐽 = 1-0 SiO maser maps and discuss the dominant pumping mechanism, which may be epoch dependent or a combination of both mechanisms.

• Solar Cycle Phase Dependence of Supergranular Fractal Dimension

We study the complexity of supergranular cells using the intensity patterns obtained from the Kodaikanal Solar Observatory during the 23rd solar cycle. Our data consists of visually identified supergranular cells, from which a fractal dimension 𝐷 for supergranulation is obtained according to the relation 𝑃 ∝ 𝐴𝐷/2, where 𝐴 is the area and 𝑃 is the perimeter of the supergranular cells. We find a difference in the fractal dimension between active and quiet region cells in the ascending phase, during the peak and in the descending phase which is conjectured to be due to the magnetic activity level.

• Estimation of Black Hole Masses from Steep Spectrum Radio Quasars

In this work, we employ a sample of 185 steep-spectrum radio quasars (SSRQs) to estimate their black hole masses from broad emission lines. Our black hole masses are compared with the virial black hole masses estimated by Shen (2010). We find that there is a large deviation between the two kinds of values if the black hole masses are estimated from broad emission line of CIV. However, both values are in agreement if the black hole masses are estimated from broad emission line of MgII or H𝛽.

• The Size of Narrow Line Region and [OIII] Luminosity Analyzed from SDSS DR7 Quasar Catalogue

In this work, we constructed a sample of 4002 quasars from SDSS DR7 quasar catalogue to calculate the electron density and size of narrow line region. We find that the electron densities are ∼ 103/cm3, and the sizes are between 27 and 775 pc. We also find that, in the ionization cone, the sizes are tightly correlated with the luminosities of [OIII]𝛾5007.

• Identification of MgII Absorption Line Systems from SDSS Quasar Catalogue

• Variability of GPS Radio Sources at 5 GHz

We carry out flux monitoring on a sample of 169 Gigahertz Peaked Spectrum (GPS) radio sources at 5 GHz and find that about one-third of them show considerable Inter-Month Variability (IMV), and these IMV phenomena are likely to be caused by interstellar scintillation (ISS). Furthermore, we find that those showing IMV tend to be point-like or core-jet structures at VLBI scale.

• Possible Outflow Formation in the Central Engine of GRBs

We investigate the vertical structure of neutrino-dominated accretion flows in spherical coordinates. In our calculation, the empty funnel along the rotation axis can naturally explain the neutrino annihilable ejection. The outflow is possible due to the positive Bernoulli function, and the luminosity of neutrino annihilation is enhanced by one or two orders of magnitude.

• Effects of Black Hole Spin on the Limit-Cycle Behaviour of Accretion Disks

We present a spatially 1.5-dimensional, time-dependent numerical study of accretion disks around Kerr black holes. Our study focuses on the limit-cycle behavior of thermally unstable accretion disks. We find that maximal luminosity may be a more appropriate probe of black hole spin than the cycle duration and influence radius.

• Effects of Toroidal Magnetic Fields on the Thermal Instability of Thin Accretion Disks

The standard thin disk model predicts that when the accretion rate is moderately high, the disk is radiation–pressure-dominated and thermally unstable. However, observations indicate the opposite, namely the disk is quite stable. We present an explanation in this work by taking into account the role of the magnetic field which was ignored in the previous analysis.

• Chandra Data Analysis of H2O Megamaser Galaxy NGC 4258

Chandra observations of NGC 4258 were analyzed to investigate the circumnuclear environment of the H2O megamaser galaxy. Its adaptively-smoothed image shows a bright nucleus and another weak source nearby. For the maser host nucleus, our preferred fitting of its spectra gives the absorption of ∼ 7 × 1022cm-2.

• Constraint on Parameters of Inverse Compton Scattering Model for PSR B2319+60

Using the multifrequency radio profiles of pulsar PSR B2319+60, two parameters of inverse Compton scattering model, the initial Lorentz factor and the factor of energy loss of relativistic particles are constrained.

• Cosmic Rays Accelerated at Cosmological Shock Waves

Based on hydrodynamic numerical simulations and diffusive shock acceleration model, we calculated the ratio of cosmic ray (CR) to thermal energy. We found that the CR fraction can be less than ∼ 0.1 in the intracluster medium, while it would be of order unity in the warm-hot intergalactic medium.

• Measurement of Plasma Ion Temperature and Flow Velocity from Chord-Averaged Emission Line Profile

The distinction between Doppler broadening and Doppler shift has been analysed, the differences between Gaussian fitting and the distribution of chord-integral line shape have also been discussed. Local ion temperature and flow velocity have been derived from the chord-averaged emission line profile by a chosen-point Gaussian fitting technique.

• Relationship among FR-I, FR-II(Q) and FR-II(G) Radio Galaxies

Based on a sample of radio galaxies, the effective spectrum index 𝛼RO (178 MHz to 0.54 𝜇m), the radio and the V-band optical luminosities are investigated for FR-I, FR-II(G) and FR-II(Q).

• Is GRB 100418A a Cosmic Twin of GRB 060614?

GRB 100418A is a long burst at 𝑧 = 0.624 without detection of associated supernova (SN).We present a detailed analysis on this event and discuss possible origins of its multi-wavelength emission. The temporal features of this event is similar to GRB 060614, a well-known nearby long GRB without SN association (possibly a Type I GRB), indicating that the two events may be cosmic twins. However, both the circumburst medium density and the GRB classification based on the gamma-ray energy and spectrum suggest that GRB 100418A would be a Type II GRB. These results make a great puzzle on the progenitors of this kind of events, if they belong to the same population.

• Correlation between the Flux Density and Polarization for Flat Spectrum Radio Quasars

In this paper, using the preliminary database of the University of Michigan Radio Astronomy Observatory (UMRAO) at the radio frequencies, we calculated the weighted polarization at 8 GHz and investigated the correlation between the polarization and the flux density for 92 flat spectrum radio quasars (FSRQs). We found that the two observations are closely and positively correlated for FSRQs. This is perhaps from a relativistic beaming effect.

• Measurement of Black Hole Mass Radio-Loud Quasars

In this work, we construct a sample of 1585 radio-loud quasars to measure their black hole masses using broad emission lines. We compare our black hole masses with the virial black hole masses measured by Shen et al. (2010).We find that there is a large deviation between them if our black hole mass is measured from the CIV broad emission line. Whereas, if our black hole mass is measured from broad emission line of Mg II or H𝛽, both the values are consistent.

• N(HI) and Jet Power/Emission in AGNs

Neutral hydrogen (HI) 21-cm absorption has been detected against very powerful radio jets. In this paper, based on Gupta’s sample (Gupta et al. 2006), we present our preliminary study of the correlations between the HI column density N(HI) and the jet power, N(HI) versus the low frequency luminosity at 408 MHz, and N(HI) versus the radio luminosity at 1400 MHz.

• Black Hole Entropy Calculation in a Modified Thin Film Model

The thin film model is modified to calculate the black hole entropy. The difference from the original method is that the Parikh–Wilczek tunnelling framework is introduced and the self-gravitation of the emission particles is taken into account. In terms of our improvement, if the entropy is still proportional to the area, then the emission energy of the particles will satisfy 𝜔 = 𝑇/360.

• Multi-Wavelength Variability in PKS 2155-304

We study multi-wavelength variability in BL Lacertae object PKS 2155-304 in the frame of the time dependent one-zone synchrotron self-Compton (SSC) model, where stochastic particle acceleration is taken into account. In this model, a homogeneously and isotropically spherical structure is assumed, the Fokker–Planck type equation which describes the evolution of the particles energy is numerically solved, and the synchrotron and self-Compton components from the spherical blob are calculated. Our results can reproduce observed spectra energy distribution (SED) and give definite predictions for the flux and spectral variability of PKS 2155-304.We find that particle injection rate, magnetic field and Doppler factor in the acceleration zone are important parameters for explaining its flaring behaviour.

• Astronomy Education for Physics Students

Astronomy is a very interesting subject for undergraduate students studying physics. In this paper, we report astronomy education for undergraduate students in the Physics Department of Guangzhou University, and how we are teaching astronomy to the students. Astrophysics has been rapidly developing since 1994, when the center for astrophysics was founded. Now, astrophysics has become a key subject in Guangdong Province, and the Astronomy Science and Technology Research Laboratory one of the key laboratories of the Department of Education of the Guangdong Province. Many undergraduate students, working under the tutorship of faculty members completed their thesis at the Center for Astrophysics in Guangzhou.

• Phase-Resolved Spectra of PSR B0525+21 and PSR B2020+28

Using the published data of multi-frequency time-aligned pulse profiles from Kuzmin et al. (1998), we calculate the phase-resolved spectra of PSRs B0525+21 and B2020+28. The results reveal that conaldouble pulsars have common M’-shaped phase-resolved spectra.

• Scintillation Velocity of PSR B0329+54

We monitored PSR B0329+54 for one year using the Nanshan 25-m radio telescope, the scintillation velocity VISS shows evidence of systematic variation with the day of the year. States of interstellar medium (ISM) are discussed.

• Multiwavelength Emission from Blazars – Conference Summary

Presentations at the Guangzhou Conference on Multiwave-length Emission from Blazars confirmed our understanding of blazars as relativistic jets closely aligned with the line of sight. Powerful new studies have been enabled by the Fermi gamma-ray satellite and new ground-based TeV facilities, which are an order of magnitude more sensitive than their predecessors. Combining gamma-ray data with VLBA radio and with optical/IR photometry has shed new light on the emission mechanisms and the jet geometry. This conference summary sets the context for the 4th blazar conference and presents some of the highlights from the meeting, as well as the questions that remain outstanding.

• List of Participants

• Author Index

• Journal of Astrophysics and Astronomy

Current Issue
Volume 40 | Issue 3
June 2019

• Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.