2002, Vol.2, No.4 (August 20, 2002)


Contents

Invited Review
  • Milestones in the Observations of Cosmic Magnetic Fields   p.293
    Jin-Lin Han and Richard Wielebinski 
    Abstract | | PDF file (1645 KB) | PS file *.gz  (2290 KB) 
Extragalactic astronomy
  • Multifrequency Polarization Variations in the Quasar 0917+624   p.325
    Shan-Jie Qian, A. Kraus, Xi-Zhen Zhang, T. P. Krichbaum, A. Witzel and
    J. A. Zensus
    Abstract | | PDF file (549 KB) | PS file *.gz  (1184 KB) 
  • A Restriction on the Duration and Peak Energy of Gamma-Ray Bursts  p.347
     En-Wei Liang, Yi-Ping Qin, Yun-Ming Dong and Guang-Zhong Xie 
     Abstract | | PDF file (118 KB) | PS file *.gz  (87 KB) 
  • The Variabilities of the Soft and Hard X-ray Components of NGC 7314 and NGC 7582 and the Distribution of Absorbing Matter in Type II AGNs    p.352
    Xiang-Hua Zou and Sui-Jian Xue
     Abstract | | PDF file (267 KB) | PS file *.gz  (365 KB) 
Stars
  • More Emission Cones: Multi-frequency Simulation of the Pulse Profiles of PSR J0437--4715   p.361
    Guo-Jun Qiao, Xu-Dong Wang, Hong-Guang Wang and Ren-Xin Xu  
    Abstract | | PDF file (224 KB) | PS file *.gz  (297 KB)  
  • AD Cancri: A Contact Binary with Components in Poor Thermal Contact   p.369
    Yu-Lan Yang and Qing-Yao Liu 
    Abstract | | PDF file (164 KB) | PS file *.gz  (152 KB) 
  • Equivalent Widths of 15 Extrasolar-Planet Host Stars   p.377
    Gang Zhao, Yu-Qin Chen and Hong-Mei Qiu   
    Abstract | | PDF file (153 KB) | PS file *.gz  (126 KB) 


Abstract

Milestones in the Observations of Cosmic Magnetic Fields

Jin-Lin Han (1) and Richard Wielebinski (2)

Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing, China
             (2) Max-Planck-Institut f¨¹r Radioastronomie, Auf dem H¨¹gel 69,
D-53121, Bonn, Germany

E-mail:  hjl@bao.ac.cn (corresponding author)

Abstract

Magnetic fields are observed everywhere in the universe. In this review, we concentrate on the observational aspects of the magnetic fields of Galactic and extragalactic objects. Readers can follow the milestones in the observations of cosmic magnetic fields obtained from the most important tracers of magnetic fields, namely, the star-light polarization, the Zeeman effect, the rotation measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio polarization observations, as well as the newly implemented sub-mm and mm polarization capabilities.
The magnetic field of the Galaxy was first discovered in 1949 by optical polarization observations. The local magnetic fields within one or two kpc have been well delineated by starlight polarization data. The polarization observations of diffuse Galactic radio background emission in 1962 confirmed unequivocally the existence of a Galactic magnetic field. The bulk of the present information about the magnetic fields in the Galaxy comes from analysis of rotation measures of extragalactic radio sources and pulsars, which can be used to construct the 3-D magnetic field structure in the Galactic halo and Galactic disk. Radio synchrotron spurs in the Galactic center show a poloidal field, and the polarization mapping of dust emission and Zeeman observation in the central molecular zone reveal a toroidal magnetic field parallel to the Galactic plane. For nearby galaxies, both optical polarization and multifrequency radio polarization data clearly show the large-scale magnetic field following the spiral arms or dust lanes. For more distant objects, radio polarization is the only approach available to show the magnetic fields in the jets or lobes of radio galaxies or quasars. Clusters of galaxies also contain widely distributed magnetic fields, which are reflected by radio halos or the RM distribution of background objects. The intergalactic space could have been magnetized by outflows or galactic superwinds even in the early universe. The Zeeman effect and polarization of sub-mm and mm emission can be used for the study of magnetic fields in some Galactic molecular clouds but it is observed only at high intensity. Both approaches together can clearly show the role that magnetic fields play in star formation and cloud structure, which in principle would be analogous to galaxy formation from protogalactic clouds. The origin of the cosmic magnetic fields is an active field of research. A primordial magnetic field has not been as yet directly detected, but its existence must be considered to give the seed field necessary for many amplification processes that have been developed. Possibly, the magnetic fields were generated in protogalactic plasma clouds by the dynamo process, and maintained again by the dynamo after galaxies were formed.

Key words: magnetic fields --- polarization --- ISM: magnetic fields --- galaxies: magnetic fields --- pulsars

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Multifrequency Polarization Variations in the Quasar 0917+624   

Shan-Jie Qian (1,2), A. Kraus (2), Xi-Zhen Zhang (1), T. P. Krichbaum (2), A. Witzel (2) and J. A. Zensus (2)

 Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing, China
             (2) Max-Planck-Institut für Radioastronomie, Auf dem Hüel 69,
D-53121, Bonn, Germany

E-mail:  rqsj@class1.bao.ac.cn    (corresponding author)

Abstract

We present a detailed analysis of multi-frequency observations of linear polarization in the intraday variable quasar 0917+624 (z = 1.44). The observations were made in May 1989 at five frequencies (1.4, 2.7, 5.0, 8.3 and 15 GHz) with the VLA and the Effelsberg 100 m-telescope and in December 1988 at two frequencies (2.7 and 5.0 GHz) with the latter. It is shown that the relationship between the variations of the polarized and total flux density is highly wavelength dependent, and the multi-frequency polarization behavior may be essential for investigating the mechanisms causing these variations. It is shown that the variations observed at 20 cm can be interpreted in terms of refractive interstellar scintillation. However, after subtracting the variation due to scintillation, three `features' emerged in the light-curve of the polarized flux density, indicating an additional variable component. Interestingly, these features are shown to be correlated with the variations at 2–6 cm, thus indicating that these features and the associated variations are due to some intrinsic causes. Moreover, a very rapid polarization angle swing of $\sim$180° observed in December 1988 which cannot be explained by refractive interstellar scintillation, may also be produced by an intrinsic mechanism. Accordingly, we use a shock model to explain the polarization variations observed at the higher frequencies, although scintillation could also exist. The shock model can explain not only the variation of intensity, but also the time variation of its degree and angle of polarization, including the rapid swing of the polarization angle. It is shown that the degree and angle of polarization of the shock need only vary slightly in order to account for the observed complicated behaviour of polarization.

Key words: radio continuum: galaxies --- polarization --- quasars: individual (QSO 0917+624)

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A Restriction on the Duration and Peak Energy of Gamma-Ray Bursts

En-Wei Liang (1,2), Yi-Ping Qin (1), Yun-Ming Dong (1) and Guang-Zhong Xie (1)

 Affiliation: (1) Yunnan Observatory, National Astronomical Observatories, CAS (NAOC), Kunming 650011, China
             (2) Physics Department, Guangxi University, Nanning 530004, China

E-mail:  qinyp@public.km.yn.cn   (corresponding author)

Abstract

Two dimensional distributions of T90 versus Epeak (or Ebreak) for three bright GRB samples have been investigated. The result shows that although both T90 and Epeak (or Ebreak) each span over a wide range, they are restricted to the region  log (T90) $\leq$  log (Epeak)+5.24. This cannot be explained by the current fireball model. It may represent a constraint on the fireball model.

Key words: gamma rays: bursts

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The Variabilities of the Soft and Hard X-ray Components of NGC 7314 and NGC 7582 and the Distribution of Absorbing Matter in Type II AGNs

Xiang-Hua Zou (1) and Sui-Jian Xue (2)

 Affiliation: (1) Department of Astronomy, Peking University, Beijing 100871
             (2) National Astronomical Observatories, CAS (NAOC), Beijing, China
                          
E-mail:  zxh@bac.pku.edu.cn  (corresponding author)

Abstract

ASCA observations of the two Type II AGNs, NGC 7314 and NGC 7582, show clear variations in the broad X-ray band (0.4 –10 keV) on short timescales $\sim$104 s. Spectral analysis indicates that they both have an absorbed hard X-ray component and an unabsorbed soft ``excess" component. To clarify the origin of the latter, we made a cross-correlation analysis of the two components. The results show that, for NGC 7314, the soft X-ray variability is proportional to that of the hard X-ray component. This indicates that the active nucleus of NGC 7314 must be partially covered and so the soft emission is a ``leaking" of the variable hard component. For NGC 7582, there is no detectable variability in the soft component, although there is a definite one in the hard component. This indicates that the variable nucleus of NGC 7582 must be fully blocked by absorbing matter, and the soft emission is most likely the scattered component predicted by the AGN unified model.

Key words: galaxies: individual (NGC 7314, NGC 7582) --- galaxies: X-rays --- galaxies: variabilities

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More Emission Cones: Multi-frequency Simulation of the Pulse Profiles of PSR J0437--4715
Guo-Jun Qiao, Xu-Dong Wang, Hong-Guang Wang and Ren-Xin Xu

Affiliation:  Department of Astronomy and CAS-PKU Joint Beijing Astrophysics Center, Peking University, Beijing 100871, China

E-mail:  gjn@pku.edu.cn   (corresponding author)
  
Abstract

Pulsar radio emission beams have been studied observationally for a long time, and the suggestion is that they consist of the so-called core and conal components. To reproduce these components is a challenge for any emission model, and that the pulse profile of pulsars changes with frequency presents even a greater challenge. Assuming a local surface magnetic structure (to produce the core or central beam) and a global dipole magnetic field (to produce the conal beams), Gil & Krawczyk (1997) applied curvature radiation to the pulse profile simulation of PSR J0437-4715 (hereafter the GK model). Here we present an alternative multi-frequency simulation of the same profiles within the framework of the Inverse Compton Scattering (ICS) model. It is obtained from our simulation (1) that besides the core, the inner cone and the outer cone, there is an outer-outer cone; (2) that the emission components of the core and cones evolve strongly with frequency. Some important differences between the ICS model and the GK model are discussed, which need to be tested by further observations.

Key words: pulsar: general --- radiation mechanisms: ICS --- pulsar: individual (PSR J0437--4715)

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AD Cancri: A Contact Binary with Components in Poor Thermal Contact

Yu-Lan Yang and Qing-Yao Liu (1,2)

Affiliation: (1) Yunnan Observatory, National Astronomical Observatories, CAS (NAOC), Kunming 650011, China
             (2) United Laboratory of Optical Astronomy, CAS
                         
E-mail:  bily@public.km.yn.cn    (corresponding author)

Abstract

We present the light curve and photometric solutions of the contact binary AD Cnc. The light curve appears to exhibit a typical O'Connell effect, with Maximum I brighter than Maximum II by 0.010 mag. in V. From 1987 to 2000, the light curve showed changes of shape: the depth of the primary eclipse increased by about 0m.056 while that of the secondary eclipse decreased by about 0m.032, so the difference between the primary and the secondary eclipses increased by about 0m.088, while there was no obvious variation in the O'Connell effect. Using the present and past times of minimum light, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of AD Cnc has continuously increased at a rate of dP/dt =4.4×10-7 d yr-1. The light curve is analyzed by means of the latest version of the Wilson-Devinney code. The results show that AD Cnc is a W-subtype contact binary with a small mass ratio of 0.267 and the two components are in poor thermal contact. AD Cnc has a component temperature difference exceeding 500 K, and exhibits a shallow contact of 3.6%. The asymmetry of the light curves is explained by the star spot model.

Key words: binaries: eclipsing --- stars: starspots

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Equivalent Widths of 15 Extrasolar-Planet Host Stars

Gang Zhao, Yu-Qin Chen and Hong-Mei Qiu 
Affiliation:  National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
                    
E-mail: gzhao@bao.ac.cn     (corresponding author)

Abstract

We present the equivalent widths of 15 extrasolar-planet host stars. These data were based on the high-resolution, high signal-to-noise ratio spectra obtained with the 2.16 m telescope at Xinglong station. The error in the Xinglong equivalent width is estimated by a comparison of these data with those given in previous studies of common stars.

Key words: stars: planetary systems --- stars: late-type

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ChJAA, 2002, Vol.2, No.4

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

Copyright 2001--2008 All rights reserved. The National Astronomical Observatories of 
Chinese Academy of Sciences, P.R. China. This Journal or parts thereof, may not be
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