ChJAA -- 2005, Vol.5, No.5

A New Method of Identifying 3D Null Points in Solar Vector Magnetic Fields

Hui Zhao, Jing-Xiu Wang, Jun Zhang and Chi-Jie Xiao

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 zhaohui@ourstar.bao.ac.cn

Abstract
Employing the Poincaré index of isolated null-points in a vector field, we worked out a mathematical method of searching for 3D null-points in coronal magnetic fields. After introducing the relevant differential topology, we test the method by using the analytical model of Brown & Priest. The location of null-point identified by our method coincides precisely with the analytical solution. Finally we apply the method to the 3D coronal magnetic fields reconstructed from an observed MDI magnetogram of a super-active region (NOAA 10488). We find that the 3D null-point seems to be a key element in the magnetic topology associated with flare occurrence.

Key Words: Sun: flares -- Sun: corona -- Sun: magnetic fields

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Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

Shao-Guang Luo^1,2 - Xue-Bing Wu¹

¹ Department of Astronomy, Peking University, Beijing 100871; luo@vega.bac.pku.edu.cn

² Shenzhen Graduate School, Peking University, Shenzhen 518055

Abstract
By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4GHz and the far-infrared (FIR) luminosity for 468 ``normal" galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the ``normal" galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 ``normal" galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index $\alpha\rm (25 \mu m, 60 \mu m)$ . These galaxies may be classified as ``AGN-powered". For ``normal" galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in ${\it heating}$ the cosmic-ray electrons.

Key Words: galaxies: active - galaxies: Seyfert - galaxies: starburst - radio continuum: galaxies - infrared: galaxies

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Separation of Different Contributions to the Total X-ray Luminosity in Gamma-ray Loud Blazars

Jun-Hui Fan^{1, 2}, Gustavo E. Romero³, Yong-Xiang Wang⁴ and Jiang-Shui Zhang¹

¹ Center for Astrophysics, Guangzhou University, Guangzhou 510400; fjh@gzhu.edu.cn

² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

³ Instituto Argentino de Radioastronomía, C.C.5, (1894) Villa Elisa, Bs. As., Argentina

⁴ College of Science and Trade, Guangzhou University, Guangzhou 511442

Abstract
The relativistic beaming model has been successfully used to explain many of the observational properties of active galactic nuclei. In this model the total emission is formed by two components, one beamed, one unbeamed. However, the exact contribution from each component in unresolved sources is still not clear. In the radio band, the core and extended emissions are clearly separated. We adopt the method proposed by Kembhavi to separate the two contributions in the X-ray emissions in a sample of 19 gamma-ray loud blazars. It is clearly shown that the beamed emission dominates the X-ray flux and the unbeamed X-ray emission is correlated with the extended radio emission of the considered objects. We also find that the ratio of the beamed to the unbeamed X-ray luminosity is correlated with the X-ray spectral index, an effect that should be a consequence of the underlying X-ray emission mechanism.

Key Words: galaxies: active-galaxies -- jets -- X-rays: galaxies

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Estimates of AGN Black Hole Mass and Minimum Variability Timescale

Guang-Zhong Xie^1,2, Luo-En Chen^1,4,5, Huai-Zhen Li^1,5, Li-Sheng Mao^1,5, Hong Dai^1,2,5, Zhao-Hua Xie³, Li Ma^1,3,5 and Shu-Bai Zhou¹

¹ National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Science, Kunming 650011; gzxie@public.km.yn.cn

² Yunnan Astrophysics Center, Yunnan University, Kunming 650091

³ Physics Department, Yunnan Normal University, Kunming 650091

⁴ Physics Department, Yuxi Normal College, Yuxi 653100

⁵ Graduate University of Chinese Academy of Sciences, Beijing 100049

Abstract
Black hole mass is one of the fundamental physical parameters of active galactic nuclei (AGNs), for which many methods of estimation have been proposed. One set of methods assumes that the broad-line region (BLR) is gravitationally bound by the central black hole potential, so the black hole mass can be estimated from the orbital radius and the Doppler velocity. Another set of methods assumes the observed variability timescale is determined by the orbital timescale near the innermost stable orbit around the Schwarzschild black hole or the Kerr black hole, or by the characteristic timescale of the accretion disk. We collect a sample of 21 AGNs, for which the minimum variability timescales have been obtained and their black hole masses ( $M_\mathrm{\sigma}$ ) have been well estimated from the stellar velocity dispersion or the BLR size-luminosity relation. Using the minimum variability timescales we estimated the black hole masses for 21 objects by the three different methods, the results are denoted by Ms, Mk and Md, respectively. We compared each of them with $M_\mathrm{\sigma}$ individually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between $M_\mathrm{\sigma}$ and Mk, none exceeding one order of magnitude, and the mean difference between them is about 0.53 dex; (2) using the minimum variability timescale with the Schwarzschild black hole theory leads to somewhat larger difference between $M_\mathrm{\sigma}$ and Ms: larger than one order of magnitude for 6 of the 21 sources, and the mean difference is 0.74 dex; (3) using the minimum variability timescale with the accretion disk theory leads to much larger differences between $M_\mathrm{\sigma}$ and Md, for 13 of the 21 sources the differences are larger than two orders of magnitude; and the mean difference is as high as about 2.01 dex.

Key Words: galaxies: active -- galaxies: nuclei -- galaxies: fundamental parameters

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Statistical Properties of a Blazar Sample and Comparison of HBLs, LBLs and FSRQs

Li-Sheng Mao^{1, 2}, Guang-Zhong Xie^1,3, Jin-Ming Bai¹, and Hong-Tao Liu^1,2

¹ Yunnan Observatory, National Astronomical Observatories, Chinese Academy of Sciences, Kunming 650011; maolisheng1981@126.com

² Graduate University of Chinese Academy of Sciences, Beijing 100049

³ Yunnan Astrophysics Center, Yunnan University, Kunming, 650091

Abstract
Making use of the 2MASS Data Release, we have searched for near-infrared (JHK) counterparts to 268 blazars from Donato et al. and obtained 238 counterparts within 5'' in the area covered by 2MASS. It provides us a sample with infrared data several times larger than the previous one of the same kind. Based on our sample and the sample by Donato et al., we have compared in detail the properties of HBLs, LBLs and FSRQs from five aspects and found that HBLs are significantly different from LBLs and FSRQs while LBLs are not obviously different from FSRQs. Our results strongly support the division of BL Lac objects into the high-frequency peaked (HBL) and low-frequency peaked (LBL) objects introduced by Padovani & Giommi and show that HBLs and LBLs are two kinds of blazar having different physical properties.

Key Words: BL Lacertae objects: general-- infrared: galaxies -- methods: statistical

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Fallback Disk-Involved Spin-Down of Young Radio Pulsars

Zi-Bo Jiang and Xiang-Dong Li

Department of Astronomy, Nanjing University, Nanjing 210093; lixd@nju.edu.cn

Abstract
Disks originating from supernova fallback have been suggested to surround young neutron stars. Interaction between the disk and the magnetic field of the neutron star may considerably influence the evolution of the star through the so called propeller effect. There are many controversies about the efficiency of the propeller mechanism proposed in the literature. We investigate the fallback disk-involved spin-down of young pulsars. By comparing the simulated and measured results of pulsar evolution, we present some possible constraints on the propeller torques exerted by the disks on neutron stars.

Key Words: stars: magnetic fields -- stars: neutron -- pulsars: individual: PSRs B0532+21, B0833+45, B0540-69, B1509-58

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Autoregressive Spectral Estimation for Quasi-Periodic Oscillations

Li Chen¹ and Ti-Pei Li^2,3

¹ Department of Astronomy, Beijing Normal University, Beijing 100875; chenli@bnu.edu.cn

² Center for Astrophysics, Tsinghua University, Beijing 100084 Key Lab. of Particle Astrophysics, Inst. of High Energy Physics, Chinese Academy of Sciences, Beijing 100039

Abstract
Modern methods of spectral estimation based on parametric time-series models are useful tools in power spectral analysis. We apply the autoregressive (AR) model to study quasi-periodic oscillations (QPOs). An empirical formula to estimate the expectation and standard deviation of the noise AR power densities is derived, which can be used to estimate the statistical significance of an apparent QPO peak in an AR spectrum. An iterative adding-noise algorithm in AR spectral analysis is proposed and applied to studying QPOs in the X-ray binary Cir X-1.

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

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Observational Characteristics of Radio Emission Related to Multi-polar Magnetic Configuration

Min Wang¹, Rui-Xiang Xie¹, Chun Xu¹, Shuo-Biao Shi¹ and Yi-Hua Yan²

¹ National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; wm@ynao.ac.cn
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Abstract
We present a large complex radio burst and its associated fast time structures observed on 2001 April 10 in the frequency range of 0.65-7.6GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar (a `bipolar + remote unipolar'), and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a `Y-type' reconnection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type III bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a `three-legged' structure, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the `inverted Y-type' (bipolar) and the `three-legged' structures (tripolar or quadrupolar).

Key Words: Sun: radio radiation -- Sun: activity -- Sun: flares

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Multi-wavelength Diagnostics of Bombardment by Non-thermal Particles in Solar Flares

Zhi Xu¹, Cheng Fang¹, and Wei-Qun Gan²

¹ Astronomy Department of Nanjing University, Nanjing 210093; xuzhi@nju.edu.cn

² Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008

Abstract
Chromospheric lines, including H $\alpha$ , Ly $\alpha$ , Ly $\beta$ and CaII K, CaII 8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Ly $\alpha$ line calculation and a smaller intensity enhancement in the H $\alpha$ line-centers is found than in the previous results of Fang et al.

Key Words: Sun: flare -- Sun: chromosphere

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Polar Coronal Holes During Solar Cycles 22 and 23

Jun Zhang^1,2, J. Woch², S. Solanki²

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 zjun@ourstar.bao.ac.cn

² Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, D-37191, Germany

Abstract
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses and synoptic maps from Kitt Peak are used to analyze the polar coronal holes of solar activity cycles 22 and 23 (from 1990 to end of 2003). In the beginning of the declining phase of solar cycles 22 and 23, the north polar coronal holes (PCHs) appear about one year earlier than the ones in the south polar region. The solar wind velocity and the solar wind ionic charge composition exhibit a characteristic dependence on the solar wind source position within a PCH. From the center toward the boundary of a young PCH, the solar wind velocity decreases, coinciding with a shift of the ionic charge composition toward higher charge states. However, for an old PCH, the ionic charge composition does not show any obvious change, although the latitude evolution of the velocity is similar to that of a young PCH.

Key Words: Sun: coronal -- Sun: particle emission -- Sun: solar wind

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Estimating the Size and Timing of the Maximum Amplitude of Solar Cycle 24

Ke-Jun Li¹, Peng-Xin Gao^1,2 and Tong-Wei Su^1,2

¹ National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; lkj@ynao.ac.cn

² Graduate University of Chinese Academy of Sciences, Beijing 100049

Abstract
A simple statistical method is used to estimate the size and timing of maximum amplitude of the next solar cycle (cycle 24). Presuming cycle 23 to be a short cycle (as is more likely), the minimum of cycle 24 should occur about December 2006 ( $\pm 2$ months) and the maximum, around March 2011 ( $\pm 9$ months), and the amplitude is $189.9\pm 15.5$ , if it is a fast riser, or about 136, if it is a slow riser. If we presume cycle 23 to be a long cycle (as is less likely), the minimum of cycle 24 should occur about June 2008 ( $\pm 2$ months) and the maximum, about February 2013 ( $\pm 8$ months) and the maximum will be about 137 or 80, according as the cycle is a fast riser or a slow riser.

Key Words: Sun: activity -- Sun: sunspot -- Sun: prediction

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A Study on the Paul-Baker System as an Instrument for Multi-object Spectrum Observation

Xiang-Yan Yuan¹, Ding-Qiang Su^{1, 2}, Xiang-Qun Cui¹ and Gen-Rong Liu¹

¹ National Astronomical Observatories, Nanjing Institute of Astronomical Optics & Technology, Chinese Academy of Sciences, Nanjing 210042; xyyuan@niaot.ac.cn

² Department of Astronomy, Nanjing University, Nanjing 210093

Abstract
Paul-Baker systems with 4 flat field and 5 flat field are studied. Their light obstructions under different f/ratios of the primary mirror are analyzed. Due to the strong f/ratio of the system, a focal length extender is designed in order to match the following fiber instrumentation, and two kinds of dispersion prism correctors are designed for correcting the atmospheric dispersion. We compare the designed Paul-Baker system with LAMOST, the national major scientific project now under construction.

Key Words: techniques: telescopes -- instrumentation: miscellaneous

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The OH Maser Line Receiving System for the Urumqi 25m Radio Telescope

Hong-Bo Zhang¹, Jarken Esimbek², Jian-Jun Zhou^1,
2, Xing-Wu Zhen³, Xi-Zhen Zhang¹ and Wen-Jie Yang⁴

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 zhanghb@bao.ac.cn

² Urumqi Astronomical Observatory, National Astronomical Observatories, Chinese Academy of Sciences, Urumqi 830011

³ Department of Astronomy, Nanjing University 210093

⁴ Beijing Institute of Tracking and Telecommunication Technology, Beijing 100094

Abstract
A maser spectral line system is newly implemented on the Urumqi 25m Radio Telescope. The system consists mainly of a cooling receiver and a 4096 channels digital correlation spectrometer. The frequency resolution of the spectrometer at the maximum signal bandwidth of 80MHz is 19.5kHz. After careful calibrations observation at the 1665MHz OH maser emission was made towards a number of sources, including W49N and W75N. The observed results demonstrate that the digital correlation spectrometer is suitable for astronomical spectral line observations.

Key Words: instrumentation: spectrometer -- OH maser

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ChJAA, 2005, Vol.5, No.5

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org

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