• J. H. Fan

Articles written in Journal of Astrophysics and Astronomy

• Praface

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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).

• 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.

• Preface

• Relativistic Beaming Effect in Fermi Blazars

The most identified sources observed by Fermi/LAT are blazars, based on which we can investigate the emission mechanisms and beaming effect in the 𝛾-ray bands for blazars. Here, we used the compiled around 450 Fermi blazars with the available X-ray observations to estimate their Doppler factors and compared them with the integral 𝛾-ray luminosity in the range of 1–100 GeV. It is interesting that the integral 𝛾-ray luminosity is closely correlated with the estimated Doppler factor, log 𝑣𝛾 𝐿𝑣𝛾 = (2.95 ± 0.09) log 𝛿 + 43.59 ± 0.08 for the whole sample. When the dependence of the correlation between them and the X-ray luminosity is removed, the correlation is still strong, which suggests that the 𝛾-ray emissions are strongly beamed.

• Possible Lognormal Distribution of Fermi-LAT Data of OJ 287

OJ 287 is a BL Lac object at redshift 𝑧 = 0.306 that has shown double-peaked bursts at regular intervals of 12 yr during the last 40 yr according to previous research. Some of the AGN 𝛾 ray power density shows a white noise process, while some others shows a red noise process. Some AGN flux presents normal or log-normal distribution. The two processes have an intrinsic relationship with centre black hole emission mechanism. We present the results of the analysis of the Fermi-LAT data. We review some problems concerning the random process.

• Correlation between 𝛾-Ray and Radio Bands for 𝛾-Ray Loud Blazars

The most identified sources observed by Fermi are blazars (Flat Spectrum Radio Quasars (FSRQs) and BL Lacertae objects (BLs). In this paper, we obtained 124 𝛾-ray loud blazars with available 𝛾-ray and radio (core and total) data. It is interesting that the 𝛾-ray luminosity have a good correlation with the radio luminosity. This phenomenon exists in the core radio luminosity (𝐿c) and total radio luminosity (𝐿t). The correlation between the 𝛾-ray and the radio luminosities is still stronger even after we eliminated the redshift effect, which suggests that the 𝛾-ray radiations in the 𝛾-ray loud blazars are strongly beamed.

• Spectral Index Changes with Brightness for 𝛾-Ray Loud Blazars

Based on Fermi 1FGL and 2FGL data, a sample of 572 𝛾-ray loud blazars are selected, in which each source has both 𝛾-ray flux and spectral index in 1FGL and 2FGL, respectively. Theoretic relation of spectral index changes depending on 𝛾-ray brightness is obtained. The correlations between the ratio of 𝛾-ray flux densities and the differences of the 𝛾-ray spectral indices are discussed for the three subclasses of HBL, LBL and FSRQs. Results show that the ratio is related with the differences for the three subclasses. It is consistent with the theoretical result and it indicates that the spectrum becomes flat as the source brightens in the 𝛾-ray band.

• Core Dominance Parameter for 𝛾-Ray Loud Blazars

In this paper, we compiled 572 blazars that have known core dominance parameter (log 𝑅), out of which 121 blazars are 𝛾-ray loud blazars. We compared log 𝑅 between 121 blazars and the rest with non 𝛾-ray detections, and found that 𝛾-ray loud blazars showed a different distribution, and their average value of log 𝑅 is greater than that for non 𝛾-ray blazars. Our analysis suggests that the 𝛾-ray emissions are strongly beamed.

• Correlation between Spectral Index and Doppler Factor for a Sample of Fermi Blazars

Relativistic beaming effect is important for blazars. In a very recent work, 𝛾-ray Doppler factors were calculated for a sample of Fermi blazars (Fan et al. 2013). In this work, we investigated the correlation between the Doppler factor and the effective spectral index, 4𝛼OX, and found an anticorrelation between them.

• Relation of Core Dominance Parameter and Extended Spectral Index for Radio Sources

The correlations between differences of two core dominance parameters and core/extended spectral index are investigated. The extended spectral index is associated with the differences very well, while there is a weak relationship between core spectral index and the differences. The average core spectral index tends to be a constant’ ∼ 0.0.

• Training in Astronomy for Physics Students

In this paper, we describe what we have done with regard to astronomy training for physics students. More and more students are interested in astronomy, they spend their summer holidays and spare time in observations and studying the observation data. Some students are familiar with using the telescope for observations, dealing with absorption line features achieved from the observations. Astronomy was selected as the key subject in Guangzhou city and Guangdong province, the laboratory for astronomy science and technology was selected as the key laboratory of Guangzhou city and that for the education department of Guangdong Province. We also provide a master degree programme for astronomy.

• Visual Method for Spectral Energy Distribution Calculation of Blazars

In this work, we propose to use The Geometer’s Sketchpad’ to the fitting of a spectral energy distribution of blazar based on three effective spectral indices, 𝛼RO, 𝛼OX, and 𝛼RX and the flux density in the radio band. It can make us to see the fitting in detail with both the peak frequency and peak luminosity given immediately. We used our method to those sources whose peak frequency and peak luminosity are given and found that our results are consistent with those given in the work of Sambruna et al. (1996).

• Error Analysis on Plane-to-Plane Linear Approximate Coordinate Transformation

In this paper, the error analysis has been done for the linear approximate transformation between two tangent planes in celestial sphere in a simple case. The results demonstrate that the error from the linear transformation does not meet the requirement of high-precision astrometry under some conditions, so the linear approximate transformation should be taken seriously.

• Astronomy Education Project for Guangdong High Schools

Guangdong province is an active area in China for astronomy education and popularization. The current status and problems of astronomy education in high schools are reviewed. To tackle these problems, an astronomy education project for high school teachers and students was initiated by Guangzhou University in 2013. The purpose and key points of the projects are introduced in this paper.

• # Journal of Astrophysics and Astronomy

Current Issue
Volume 40 | Issue 2
April 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.