2001, Vol.1, No.4 (August 20, 2001)

Contents      

LETTERS

Is the Variable X-ray Source in M82 due to Gravitational Lensing?
Da-Ming Chen  ................................................................. p.287
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Do Globular Clusters Harbor Black Holes?
Xian-Zhong Zheng  ............................................................. p.291
Abstract | | PDF | PS (*.gz)  | PS (*.zip)
RESEARCH PAPERS


Spectral Reversal and Stratification of the Jet in 3C 273
Shan-Jie Qian, Xi-Zheng Zhang, T. P. Krichbaum, A. Kraus,
A. Witzel and J. A. Zensus  ................................................... p.296
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

VLBI Observations of the Blazar 1611+343 at 5 GHz
Tao An, Xiao-Yu Hong, Wei-Hua Wang, Dong-Rong Jiang and Yong-Jun Chen  .......  p.305
Abstract | | PDF | PS (*.gz) | PS (*.zip)

Timing in the Time Domain: Cygnus X-1
Ti-Pei Li  ..................................................................   p.313
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Vilnius Photometry and Reddening of the Young Open Cluster NGC 6913
Jun-Jie Wang and Jing-Yao Hu  ...............................................   p.333
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

IRAS 19111+2555 (=S Lyr): A Possible Silicate Carbon Star
Pei-Sheng Chen and Xun-Hao Wang  ............................................   p.344
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Hydrodynamic Evolution of GRB Afterglow
Ji-Rong Mao and Jian-Cheng Wang  .............................................  p.349
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Entropy of Dilatonic Black Hole due to Arbitrary Spin Fields
You-Gen Shen and Chang-Jun Gao  ..............................................  p.357
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Harmonic Structures of Gyrosynchrotron Radiation and Cyclotron Maser Instability
Ai-Hua Zhou and Guang-Li Huang  ..............................................  p.365
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Flux Calibration of the BATC Survey and Its Application for Checking the Consistency of the Oke-Gunn Standards
Xu Zhou, Zhao-Ji Jiang, Sui-Jian Xue, Hong Wu, Jun Ma and Jian-Sheng Chen  ...  p.372
Abstract | | PDF | PS (*.gz)  | PS (*.zip)

Abstract

Abstract

We explore the possibility of attributing the recent discovery of the variable hard X-ray source CXO M82 J095550.2+694047 in M82 to the gravitational magnification by an intervening stellar object along the line of sight acting as a microlens. The duration of the event (>84 days) allows us to set robust constraints on the mass and location of the microlensing object when combined with the dynamical properties of the Galactic halo, M82 and typical globular clusters. Except for the extremely low probability, the microlensing magnification by MACHO in either the Galactic halo or M82 halo is able to explain the X-ray variability of CXO M82 J095550.2+694047. It is hoped that the lensing hypothesis can be tested soon by measurement of the light curve.

Key words: X-rays: stars --- Galaxies: individual: M82 --- gravitational lensing

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Abstract

It has been firmly established that there exists a tight correlation between the mass of the central black hole and velocity dispersion (or luminosity) in elliptical galaxies, ``pseudobulges'' and bulges of galaxies, although the nature of this correlation still remains unclear. We explore the possibility of extrapolating such a correlation to less massive, spherical systems like globular clusters. In particular, motivated by the apparent success in the globular cluster M15, we present an estimate of the central black hole mass for a number of globular clusters with available velocity dispersion data.

Key words: black hole physics --- globular clusters: general --- galaxies: general

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Abstract

Quasi-simultaneous VLBI observations at 15-86 GHz have shown that in the classical superluminal radio source 3C 273, the spectral index ( ) has a systematic variation along the jet. For epoch 1995.15, a spectral reversal was observed at core distance of 1.5 mas, where the superluminal knot C12 located. Similarly, for epoch 1997.18, two spectral reversals were observed at core distances of 1.8 mas and 4.2 mas, where superluminal knots C11 and C14 were, respectively. These spectral reversals are associated with local maxima of the jet width. We suggest that this phenomenon may be related to a stratification of the jet structure, i.e., its physical parameters (flow velocity, Doppler factor, electron density and energy, magnetic field strength, etc.) are substantially dependent on the distance from the jet axis. These properties may be naturally formed through gasdynamic processes when the jet expands into a lower pressure ambient medium.

Key words: galaxies: active --- galaxies: compact --- quasars: individual: 3C 273 --- galaxies: jets --- radio continuum: galaxies --- radiation mechanisms: non-thermal

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Abstract

Quantities characterizing temporal property, e.g., power density, coherence, and time lag, can be defined and calculated directly in the time domain without using the Fourier transformation. Spectral hardness, variability duration, and correlation between different characteristic quantities on different time scale can be studied in the time domain as well. The temporal analysis technique in the time domain is a powerful tool, particularly in studying rapid variability on short time scales (or in high frequencies). Results of studying variabilities of X-rays from Cyg X-1 with the analysis technique in the time domain and RXTE data reveal valuable clues to understanding production and propagation processes of X-rays and structure of accretion disk in the black hole system.

Key words: methods: data analysis --- stars: individual (Cygnus X-1) --- X-rays: stars

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Abstract

87 stars in the NGC 6913 field with both UBV and Vilnius photometry are selected to be the sample. The membership probability of the stars is greater than 50%. The correlation among Vilnius photometry, UBV photometry and reddening in the cluster is reviewed. It is found that the photometry in the Vilnius X, Y and Z bands can be used to make rough spectral classification. The values of E(B-V) are well correlated with the Vilnius colors of X-Y, Y-Z, Z-V and V-S in NGC 6913. The ratio of (V-S)/(Y-Z) of the MPCM (Most Possible Cluster Members) is a constant (1.30 0.06), and has no effect on the values of E(B-V), (B-V)₀ and V₀. Comparing with the observational data of all the stars of NGC 6913 region, we propose that the value of (V-S)/(Y-Z) can probably be used to select the preliminary candidates of one open cluster. In addition, 12 variable stars are discovered in the NGC 6913 region, in which star #155 has a variation with an amplitude of 4.25 mag.

Key words: Galaxy: open clusters and associations --- ISM: dust, extinction

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Abstract

The properties and classification of IRAS 19111+2555 have so far not been well determined. We collect all the available information and data of this star, and take the data obtained by IRAS LRS and ISO SWS to discuss its properties and classification. The star is found to have a 3.1m feature in absorption and a 10m feature in emission, so it is possibly a new silicate carbon star.

Key words: stars: AGB and post-AGB --- stars: carbon --- infrared: stars

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Abstract

Using the membrane model based on the brick-wall model, we calculate the free energy and entropy of dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a numerical coefficient between them.

Key words: black hole physics --- entropy --- spin

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Abstract

The harmonic structures of the gyrosynchrotron radiation are studied and compared with the results of the electron cyclotron maser instability. The structures only appear at lower harmonics (s < 10), and their peaks deviate by a small amount from integer harmonic numbers. The amplitudes of harmonic structures of the extraordinary modes are usually larger than that of the ordinary modes. The numbers and amplitudes of harmonic structures increase with increasing electron energy spectral index and propagation angle . All the properties of harmonic structures are consistent with the predictions of the electron cyclotron maser instability in an extremely magnetized plasma on the basis of Maxwell and Vlasov equations. The physical relations between gyrosynchrotron radiation and cyclotron maser instability and a possible application of the properties of the harmonic structures are discussed.

Key words: Sun: activity --- Sun: radio radiation --- Sun: magnetic fields

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Abstract

Four Oke-Gunn (OG) standards, HD 19445, HD 84937, BD+26 2606 and BD+17 4708 are used as standard stars for flux calibration in the BATC project. They are also widely used in the visual wavelength region in many other photometric projects. Over the years we have observed on 58 good photometric nights, and the data obtained are used for flux calibration. Normally two or three OG standards are observed in every photometric night. The data are used for getting the atmospheric extinction coefficients and instrumental magnitude zero point. We also use these data to make inter-comparisons among the magnitudes of these standard stars. As a result, we found the magnitudes of HD 19445, HD 84937 and BD+17 4708 to agree well with those estimated in previous work to within 0.03 magnitude. However, BD+26 2606 shows a larger deviation especially at short wavebands. Possible reasons are analyzed and the revised magnitudes are obtained for these standards. It is shown that the quality of flux calibration of the BATC fields is significantly improved by applying the new magnitudes.

Key words: techniques: photometric: calibration

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