Warm CO Gas and Cold Dust in Galaxies

Richard Wielebinski
Max-Planck-Institut für Radioastronomie, Bonn

The recent years have seen the 'closing' of the window between radio astronomy and far infrared observations. Several telescopes exist capable of sub-mm wavelength observations, more are under construction. Radio astronomy at cm wavelengths studies thermal (free-free) emissions from hot gas and non-thermal radiation from magnetic fields and relativistic electrons. When we move into the mm wavelengths range we can study many molecular lines as well as emission from cold dust. At sub-mm wavelengths the lines become a forest and the continuum emission comes from warm dust. In recent years we have made studies of nearby galaxies with the Pico Veleta 30m telescope in the CO(1-0) and CO(2-1) line, as well as in ? = 1.2 mm radio continuum. Some of the studied objects were re-observed with better angular resolution with the Plateau de Bure mm-wave interferometer. The HHT telescope on Mt.Graham was used to make observation in the CO(3-2) and CO(4-3) lines as well as in ? = 870µ radio continuum. The combination of all these data allow us to study warm CO gas and cold dust in these galaxies. A surprising result was the discovery of widely distributed warm gas in galaxies. I will in addition describe the project APEX, a 12m pathfinder radio telescope for sub-mm wavelengths to be constructed on the Chajantor site in Chile at the elevation of 5080m. I will also mention briefly the present status of the ALMA projece

Studies of massive star formation with centimeter-millimeter emission

Yuefang Wu
Astromony department, Peking University

Millimeter-centimeter lines brought us many remarkable discoveries in the regions of massive star formation. Centimeter continuum emission also make it possible for a signpost of massive star forming-UC HII regions tobe clearly established. Owing to the relative distance and complex birth places of massive stars and their rapid evolution, the characteristics of the earliest stage of massive star formation are too difficult to catch. Studies on massive star formation are lagging behind compared to the studies on low-mass star formation. Now because of the advancement of technology the difficult problems for deeply probing the earliest phase of massive stars are being solved. Phenomena of evolution phases earlier than UC HII regions are observed. Studies for massive star formation are in bloom.


Christian Henkel
MPIfR, Bonn

To date five molecular species are known to show maser emission in external galaxies: H2O, OH, H2CO, CH, and SiO. While SiO and CH masers appear to be similar to those observed in the Galaxy, but often more luminous, H2CO, OH, and H2O masers can be principally different. Of particular interest are the water vapor masers that provide the only emission lines from accretion disks that can be directly imaged in active galactic nuclei. The properties of this emission, emphasizing the derivation of phyical parameters including temperature, magnetic field, disk stability, mass accretion rate, heating of the disk, disk orientation, spin direction and degree of warping, will be discussed. Emphasized are also H2O masers associated with nuclear jets. The physics of OH mega-and gigamasers, their association with ultraluminous galaxies, and their high potential relevance for cosmological studies will be another topic of this talk.

A study of megamaser galaxies

Zhiyao Yu
Shanghai Astronomy Observatory

This paper has studied the infrared property of OH megamaser galaxies, and its relationship with the observational character of OH megamaser.

Multiple line study of HH106

Junzhi Wang
Astronomy Department, Peking University

Not available yet!

Feasibility study on the FAST

Rendong Nan

A Five hundred meter Aperture Spherical Telescope, FAST, is proposed to be built in the karst region of southwest China. This project is also an effort for the international cooperation in the Kilometer Square Array - SKA. The feasibility study on the FAST concept with theoretical analysis and model experiments were funded in 1999, and its results has been evaluated to be successful at the end of 2001 by the CAS. Study phase of the FAST approved the feasibility of the layout of the telescope on the whole. Many questions, however, were also brought forward from those model tests - reliability, maintenance and the construction cost. An improved down scale models of the cable feed supporting and cable-net active reflector are under construction and experiment.

The 100-m Effelsberg Telescope and the Milky Way

Ernst Fuerst
MPIfR, Bonn

The Effelsberg 100-m radio telescope began it's astronomical operation in 1971. For about 30 years it was the largest fully steerable radio telescope. Observations can be done from the prime focus as well as from the secondary, gregorian, focus. The large focal length of the secondary focus allows the installation of a large number of receivers and multi-feed systems. Some technical details of the telescope are described, which are relevant for the quality of the observations. Since the beginning, the 100-m radio telescope contributes to all fields of radio astronomy: radio continuum, spectroscopy, pulsar research and VLBI. The telescope is well suited to map large areas of the sky in the radio continuum, in total intensity and polarization. As an example, the plane of the Milky Way at radio waves is presented. Such data in combination with follow-up measurements at other radio frequencies provide spectral and polarization information on various objects of the Milky Way. A few examples are discussed. At the 100-m telescope, observations at wavelengths shorter than 1~cm will become more and more important. Large arrays will help to speed up mapping of extended areas. A proposal exists to improve the sensitivity of the 100-m radio telescope especially at short wavelengths. A comment on this project is given.

VLBI facilities and observations in China

X. Y. Hong1, J. Zhang2, X. Z. Zhang1

  1. Shanghai Astronomical Observatory, CAS, Shanghai 200030, China
  2. Urumqi Astronomical Observatory, NAOC, CAS, Urumqi, China
There are two radio telescopes which working for VLBI observations in China. One is near Shanghai and the other is near Urumqi. They are the members of the European VLBI Network (EVN) and International VLBI Service for Geodesy and Astrometry (IVS). The new developments of the two VLBI stations and the joint international VLBI observations are described. We will also introduce a new VLBI correlator in Shanghai.

Current Projects and New Initiatives on Radio Telescope

Dehua Yang

With the development of radio astronomy, observation is covering the whole band of electromagnetic radiation and even the cosmic rays, especially the section of wavelength between submillimeter and millimeter. Thus, more powerful observing facilities are needed. This paper reviews current projects and new initiatives on radio telescope mainly working at submillimeter and millimeter bands, and describes key technology and special consideration involved on design of such telescopes . The paper also briefs radio telescope programs running in China.

An introduction to the new Miyun 50m radio telescope

Chengjin Jin

An introduction to the new Miyun 50m radio telescope will be given, including the main scientific driver and the specifications of the telescope. The overall layout design and the working schedule will also be introduced.

A Study of Optimization of the Focus in the FAST

Shengyin Wu

It is important to choose an optimal focus in the project FAST to ensure a minimum r.m.s. displacement from a spherical surface to a parabolic reflector, a minimum deviation of spherical (or planar) panel elements from the parabola simulated, a minimum relative displacement of panel elements for simulating a parabolic reflector from the neutral spherical surface and a feasibility of utilization of multi-parabola fitting scheme. An optimal focus could also reduce problems due to differences of radial arc length and reflector area between parabolic reflector simulated and corresponding spherical surface as far as possible and errors in programming and adjusting the panels. A choice of the focus would influence the design and installation of any multi-beam feed on the FAST. A study of optimization of focus in the FAST is introduced in this report.

An optimal UV coverage design of KARST for SKA

Yan Su

China is contributing to the FAST project, as a pilot of international project SKA. The Chinese SKA, KARST, consists of about 30 individual FAST type elements, each roughly 200 m in diameter. More than 300 hundred candidate karst depressions in south of Guizhou Province in China have been detected. How to arrange the 30 elements array, and get the best UV coverage is one important problem. We consider one possible optimized way to sort it out here.

Sub-mm Dust Emission in Massive Star Forming Regions

Ruiqing Mao
PMO, Nanjing

We present 870 micron images of about 80 massive star forming regions taken at 22" resolution with a newly installed 19 pixels bolometer on the HHT-10m. Strong sub-mm dust emission is detected for almost all sources associated with 6.7GHz methanol masers with only two exceptions toward which there was no dust emission under a noise level of 0.2 Jy. Some interesting sources were also mapped in the CO(3-2) and outflow activities are found to be quite common in massive star forming regions. The relationships among massive YSOs, molecular outflows and methanol masers are also discussed.

Spectral system of Urumqi telescope and water maser study

Jarken.E, Y.Wu
Astronomy Department, Peking University

Introduction of Spectral system of Urumqi telescope. We collected noth and sourth hemisphere water masers and analyzed global properties of all water masers associated with IRAS-MSX sources, discussed relation berween water masers with pumping mechanism.

The Mapping Study of High-velocity Gas near Young Stellar Objects

Yang Wang , Yuefang Wu
Astronomy Department, Peking University

It is now generally believed that during the earliest stages of evolution, stars undergo a phase of very energetic mass ejection ,frequently characterized by the occurrence of massive bipolar outflows of molecular gas. The broad molecular emission line is an evidence of high-velocity molecular gas, but it also the evidence of turbulence and rotation. So mapping the region of high-velocity is an effective method to identify the outflows around young stellar. The Outflow Statistical Catalog (Wu et al. in 1996) still have some object that did not map to identify the outflows composition. Observation were made with the 13.7m telescope at Qinhai Station for ten sources. The result and a discussion are present in this paper.

A bipolar molecular outflow near IRAS 02461+6147

Yun Shi
Astronomy Department, Peking University

Not available yet!

CO and its isolate study for IRAS 00117+6412

Ming Zhao
Astronomy Department, Peking University

Not available yet!

Mapping studies of high velocity gas sources

Wentao Yu
Astronomy Department, Peking University

Not available yet!

A study of molecular outflows

K. Sun, Y. Wu
Astronomy Department, Peking University

Not available yet!

A mapping study for S106

Y. Wei, Y. Wu
Astronomy Department, Peking University

Not available yet!

Observations of Galactic magnetic fields

Wolfgang Reich
MPIfR, Bonn

Radioastronomical methods are used to reveal the properties of Galactic magnetic fields. Their strength and regularity are derived from multi-wavelengths observations of synchrotron emission and its percentage polarization. Faraday effects cause depolarization and enhance the rotation measure of extragalactic sources, pulsars and supernova remnants. Rotation measures carry information on the magnetic field strength along the line of sight coupled to the warm interstellar medium. Recently, substantial progress has been made in Galactic polarimetry tracing magnetic fields on scales ranging from sub-pc to several hundred pc. That is essential to understand the average field properties on kpc scales, which is at present easier to observe and hence better known for nearby normal galaxies. New results from polarization observations made with the Effelsberg 100-m telescope are discussed. Multi-frequency data show a highly structured magneto-ionic interstellar medium. High frequency observations reveal the unusual properties of the poloidal magnetic field in the Galactic Centre region. Polarized Galactic high latitude emission acts as a 'foreground' for observations of the cosmic microwave background and needs to be better known at high frequencies.

Large scale surveys of the Galaxy

Patrica Reich
MPIfR, Bonn

The radio luminosity of normal galaxies is not very high and requires the largest telescopes to observe them. Principally the best case to study normal galaxies is our own one, however, our unfavourable location within the Galaxy makes it necessary to observe large-scale surveys at different frequencies in order to derive physical properties of the Galaxy. For a long time the 408 MHz all-sky-survey and the 1420 MHz survey of the northern sky have been the most reliable surveys to perform these studies. In the last years the 1420 MHz survey has been extended to an all-sky survey and also at 22, 45 and 2625 MHz large portions of the Galaxy have been published. Now there is an unprecedented database for Galactic studies available. One key information derived from those data is the distribution of spectral indices. For their computation the absolute calibration of those surveys is the most important requirement. The absolute zero levels and the impact of other insufficiencies of the surveys on the spectral index maps will be discussed. Some preliminary results will be presented.

The global structure of magnetic fields in our Galaxy

JinLin Han

Not available yet!

The 'tomography' of the magnetic interstellar medium

Richard Wielebinski
Max-Planck-Institut für Radioastronomie, Bonn

The Galaxy is a conglomerate of many components. We observe starlight, radio continuum, HI radio line, various molecular lines, UV and IR radiation, X-ray emissions and even ?-ray events. Recent observations have shown that all this interstellar medium is permeated by magnetic fields. We know little about the origin of magnetic fields. We have just started to trace the distribution of magnetic fields in our Galaxy, nearby galaxies, radio galaxies and clusters of galaxies. At this stage we can say that every object seems to possess a magnetic field. However we still cannot decide if the magnetic fields are just a consequence of rotation only or if they play an active role in the dynamics of galaxies. I will present some recent observations on our Milky Way and for nearby galaxies. In particular I will show how different types of observations can be combined, especially for our Galaxy, to reconstitute the distribution of the magnetic fields in three dimensions: hence perform a 'tomography' of the magnetic interstellar medium.

Velocity stratification, azimuthal magnetic field and the RM sky

Hui Men

Not available yet!

Radio observations of the magnetic fields in galaxies

Marita Krause
MPIfR, Bonn

Radio observations of the continuum emission turned out to be the most powerful tool to study the magnetic fields in galaxies. The total intensity of the synchrotron emission gives the strength of the total magnetic field. The linearly polarized intensity reveales the strength and structure of the resolved regular field in the plane of the sky whereas a map of the Faraday rotation measure gives the strength and direction of the field components along the line of sight. Combining both data sets enables us to perform a 'tomography' of the magnetic field. The magnetic field in flat galaxies turned out to be mainly parallel to the disk. Well-ordered magnetic fields with a large-scale spiral structure are found in grand design, flocculent and even irregular galaxies. In grand-design galaxies the magnetic fields are aligned parallel to the optical spiral arms. The strongest regular fields are found in the interarm regions, sometimes forming 'magnetic spiral arms' between the optical arms. Faraday rotation of the polarization vectors reveals coherent large-scale fields as expected by the generation of a large-scale dynamo. A few galaxies show a dominating axisymmetric spiral pattern. However, the majority of field structures in galaxies seem to be a superposition of different dynamo modes. Recent studies of magnetic fields in barred galaxies and spiral galaxies seen edge-on will also be discussed.

Gaseous halos and the disk-halo interaction in spiral galaxies

Ralf-Juergen Dettmar
Astronomical Institute, Ruhr-University Bochum, D-44780 Bochum, Germany

Ever since the first evidence for radio-continuum halos in the Milky Way and other galaxies - such as in the prototypical case of NGC 4631 - the physical processes for the origin of gaseous galactic halos were mainly sought in the feedback of energy into the interstellar medium (ISM) by young stars through winds, the interstellar radiation field, and (multiple) supernova explosions. >From this general idea the concept of the disk - halo interaction emerged in which the disk medium can connect to the halo. This is described in different model approaches in term of galactic fountains, chimneys, or super - bubble - outbreak by theory. Observational support for the idea of such a large scale matter exchange between disk and halo comes from observations of gaseous halos in external galaxies (e.g., Dahlem 1997, Dettmar 1998). While several phases of the ISM - from cold HI to X-ray coronae - have meanwhile been found in the halos of spiral galaxies. the H+ represents a particularly important constituent, since it is relatively easily observed in the optical (Dettmar 1992, 1998). Therefore, imaging in and spectroscopy of optical emission lines allow us to study the distribution and excitation of this Diffuse Ionized Gas (DIG, or WIM for Warm Ionized Medium) with a spatial resolution not achievable for other phases of the ISM in external galaxies. In order to demonstrate this point we will present results from a new quantitative survey for H+ halos of edge-on galaxies (Rossa & Dettmar 2002). The data confirm that the presence of DIG in the disk-halo interface of spiral galaxies is related to star formation processes in the underlying disk and allow us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. Comparing some recent observational results for diagnostic emission lines with model predictions from photoionization and shock models (Tullmann & Dettmar 2000) we demonstrate that the origin and excitation of the DIG is, however, still not completely understood and that a discussion gives indeed important constraints for models of the ISM in general and on the disk-halo connection in particular. In comparison with similar for the Milky Way the need for an additional heating source is established. Special emphasis will be given to some recent developments. We will discuss now kinematical information for the DIG layer in NGC 5775 from ESO/VLT long-slit spectra in connection with the magnetic field structures in the halo of this object as deduced from VLA radio-continuum jpolarization data (Tullmann et al. 2001). Finally, the role of dust for the physical process in the disk-halo interface will be addressed.

Cosmic Plasma Dynamo

Zhiliang Yang
Department of Astronomy, Beijing Normal University

The plasma is described by magnetic field or current. The general MHD is in the way describing plasma with magnetic field. However, it is not suitable for the magnetic generation (Alfven, 1981, Cosmic Plasma). To describe the dynamo effect, MHD is not a right way. The particle property should be considered in dynamo effect. Eventually with a infinite field description for a finite object by the MHD is erroneous. The polarization of plasma is important for a finite object consisting of plasma. The dynamic equation for moving plasma with its polarization considered is presented in this paper. It may be an extended MHD equation. In low frequent electromagnetic field, polarization is important. From the extended MHD equations considering the polarization, we get the dynamo effect in plasma.

Modelling the evolving cosmological magnetic fields

Xiaopeng You

Not available yet!

Magnetic fields in galaxies: their origin and their impact on the ISM

Katia Ferriere
Obs-mip, France

In the first part of the talk, I will discuss the origin of galactic magnetic fields. After showing that the primordial field theory is in disagreement with observations, I will present the dynamo theory in which large-scale magnetic fields are amplified under the combined action of the large-scale galactic differential rotation and small-scale cyclonic turbulent motions. I will describe the threefold role played by turbulent motions in the dynamo process: generation of magnetic field in the direction perpendicular to the prevailing field (alpha effect), vertical transport of magnetic field lines, and turbulent magnetic diffusion. I will then present numerical solutions of the galactic dynamo equation for a supernova-driven turbulence. In the second part of the talk, I willdiscuss the impact of galactic magnetic fields on the interstellar medium. Through the Lorentz force, they affect both the dynamics and the spatial distribution of the ordinary matter at all scales. At large scales, they help to support it against its own weight, while they confine cosmic rays to the galaxy. At smaller scales, they oppose the expanding gas motions driven by supernova explosions, they constrain the random motions of interstellar clouds, and they control the star formation process. In addition to their dynamical role, they provide a heat source for the interstellar gas through magnetic reconnection.

Discovery of Double Quasi-Periodic Oscillations in Sgr A*

Jun-Hui Zhao
CfA, Harvard

We report the discovery of double quasi-periodic oscillations in the radio flux density of Sgr A* based on the densely sampled radio light curves observed with the VLA in the past two years. The new VLA data shows both the quasi-periodic oscillations at periods of 132 and 330 days. The ratio of the two periods appears to be 2.5, which is a suggestive of a resonance of orbital motions occurring in the accretion disk around the supermassive black hole at the Galactic center.

Magnetic fields in late-type stars

Jianrong Shi

Not available yet!

Solar Radio Spectrometer Observations of Burst Events During 23rd Solar Maximum

Yihua Yan

Not available yet!

Pulsars: Some Observational Constraints on Theoretical Models

A.. Jessner
MPIfR Radio observatory Effelsberg

Pulsar observations at Effelsberg have a long history and cover a wide frequency range (800MHz - 43 GHz). Our equipment enables us to make high quality radioastronomical observations in all important aspects of pulsar study. Scatter broadening of nine pulsars was investigated at over a wide range of frequencies with the result that the broadening times are larger than predicted and follow a flatter frequency dependence (n-3.4) than expected from standard scattering theories. High precision pulsar timing observations enabled us to determine the influence of spin-orbit coupling on the orbital parameters of PSR J2051-827 and the radius of the companion. The Effelsberg radiotelescope has excellent polarisation characteristics. A determination of rotation measure for 46 pulsars enabled us to conclude, that no large scale reversals of the magnetic field occur within 85°<l<245° and the magnetic field follows the local spiral closely between 150°<l< 245°. Because of our support for the common EPN Dataformat it has become easy and nearly a routine matter to participate in simultaneous multifrequency-multitelescope single pulse polarisation studies with our partners in Europe and India. Investigating single Pulses of PSR B0329+54 simultaneously received in Jodrell Bank and Effelsberg, it became evident, that between the two frequencies, the centre component correlates strongly for circular polarisation but not for linear polarisation, whereas both outer components exhibit the converse behaviour. Pulsars show unexpected behaviour at the very high radio frequencies (> 10 GHz) where they are still visible,- if only for the Effelsberg Instrument. In a number of cases the received fluxes are higher than expected, suggesting an up-turn in their spectrum. Furthermore, their variability (modulation index) is higher than predicted, it is likely that we observe intrinsic intensity variations at these frequencies. Observational evidence is also at odds with canonical models of the magnetosphere: Radioemission as observed could not escape a magnetosphere with the often assumed high densities (>1000 nGJ) and Lorentz factors (g>100). Various forms of curvature emission are often invoked by observers as an explanation of radioemission. However the implied emission heights, Lorentz factors and densities cannot explain the observed intensity of the radio emission.

The radial structure of radio emission region of pulsar

Xinji Wu
Department of Astronomy, Peking University

The study of radial structure of radio emission region is important topic in the study of the pulsars. The altitude of emission region cannot be derived directly from observation. Emission altitude can be expressed as a function of frequency . The method of the K parameter analyses was used to calculate the power law index of altitude-frequency relation directly from observation data at different frequency. The values of are obtained for 18 pulsars at two frequencies of 610MHz and 1408MHz and for 3 pulsars at more than three frequencies. The average value of power law index is 0.27, which indicate the emission altitude increase with decreasing frequency and the radial structure is compact.

The Observations of Mode-Changing Phenomenon of pulsars at UAO

Ali Esamdin
Urumqi Astronomical Observatory, NAO, Urumqi 830011
Department of Astronomy, Peking University, Beijing 100871

We reported the results of pulsar mode-switching phenomenon observation obtained at 327MHz and 610MHz, using the 25m radio telescope of Urumqi Astronomical Observatory, NAO. Several different shape of pulsar integrated profiles at two different frequencies are presented. We also discuss some of the characteristics of mode-changing in this paper.

Recent pulsar results from Parks

Dick Manchester
ATNF, Australia

Not available yet!

Pulsar observations at Urumqi Observatory - present and future

Na Wang
NAOC, Urumqi

We present the status and results of pulsar observations in China. Observations commenced with a pulsar timing system at the 25-m Urumqi Nanshan telescope in mid-1999; these were the first regular and high-quality pulsar observations in China. The center frequency of this system is 1540 MHz, and de-dispersion is provided by a 2x128x2.5MHz filterbank/digitiser system. Observations over more than one year have resulted in updated rotation parameters for 74 pulsars. Comparing with earlier observations we showed that long-term period and period-derivative fluctuations may be dominated by unseen glitches. Taking advantage of the available telescope time, we are also monitoring the variation of pulsar scintillation dynamic spectra for a few strong pulsars. Scintillation parameters are measured and their variations are under study. We are planning to built a new system at a lower frequency so that frequency-dependent pulsar properties can be investigated.

An accretion disk model for periodic variations of PSR B1828-11
Qiao G.J., Xue Y.Q, Xu R.X. Wang H.G., Xiao B.W.
              Astronomy Department, Peking University

Stairs, Lyne and Shemar(2002) found long-term, highly periodic and correlated variations in both the pulse shape and the rate of slow-down of the pulsar PSR B1828-11. They emphasized that it is evidence for free precession in a pulsar. But which is difficult to understand theoretically, because torque free precession of a solitary pulsar should be damped out by the vortices in its super-fluid interior. Some authors such as Jones & Andersson (2001), Link & Epstein (2001), Rezania(2002), proposed various kinds of model to explain this phenomena. Here we present an accretion disk model for this pulsar. Under reasonable parameters, the observed phenomena can be understood. If this case can be confirmed, it may be form a link between radio pulsars and anomalous x-ray pulsars and presents a support for fossil disk model of anomalous x-ray pulsars.

Radio pulsar death

Bing Zhang
Pens, University

In this talk, I'll review the recent progress in understanding the pulsar particle acceleration and emission mechanisms, focusing on the polar cap scanario. I'll describe how pair formation, an essential condition for pulsar radio emission, is sustained in active pulsars through one photon pair production from both the curvature and inverse Compton seed photons, or sometimes through two photon production. In case of super-critical magnetic fields, some more exotic processes, such as photon splitting and bound pair formation, will be also discussed. These effects will be synthesized to discuss the radio pulsar death both in the conventional long-period regime due to the turn off the active accelerator, and in the high magnetic field regime (both for high magnetic field pulsars and magnetars) due to the possible suppression of the free pair formation.

A possible interpretation for the spectral behavior of pulsar average profiles

Wang, H.G. Qiao, G.J. Xu, R.X.
Department of Astronomy, Peking University

Recently, Mitra & Rankin (2002) identified three kinds of spectral behavior of pulsar average profiles with conal component pairs: for the first two groups, the peak separation or the pulse width exhibits pronounced narrowing as frequency increases; for the third type, it shows almost no spectral change in separation and width at all. In this paper we present a novel interpretation for these phenomena. As to the first two types of behavior, our interpretation is essentially different from the widely accepted explanation called "radius-to-frequency" mapping, which suggests that lower radio frequencies are emitted at higher altitudes. The implication towards the structure of emission region is discussed.

The initial period of pulsars

Zhankui Huang
Department of Astronomy, Peking University

The initial period of pulsar are important to understand the process of the neutron star formation, and the nature of equation of state of neutron star maters. There are two ways of to determination. The theoretical one use the EOS to the possible initial period, the other method is to presume the pulsar slow down by magnetic dipole emission. The Chandra observation of Crab pulsar and Vela pulsar give strong evidence that the nebula is symmetric about the spin axis and the proper motion are parallel to this axis. If the coincidence is common, then the processes that cause this coincidence are asymmetric dipole emission. Based on this theory, we can use the proper motion data to derive the initial period. The observed velocity of pulsars may be combination of three factors that is the progenitor orbital velocity, the kick of asymmetric explosion, and the off-center dipole emission. So we think the derived value is the lowest limit of initial period.

Individual pulses of PSR J0437-4715

Xianghua Li

Not available yet!

Further investigation of the central beam of PSR B1237+25

Qiao,G.J.,Li,K.J, Wang,H.G.,Xu,R.X. & Liu,J.F.
Astronomy Department, Peking University

Core emission component has been identified by observations (Rankin, 1983, Lyne & Manchester, 1988), which presents a challenge for various pulsar radio emission models. Using Gaussian-components fitting, Qiao et al (2000) pointed out that the central or core emission beam may be hollow. In this paper, by developing a quantitative criteria for the fitting procedure, we prove that the mean profile of the pulsar PSR B1237+25 is composed of six Gaussian components, which confirms that the core beam is hollow. From the fitted results, further information of the radio emission region is obtained based on the Invert Compton Scattering model (ICS model). The Lorentz factor of secondary particles for this pulsar is estimated to be 1000 ~3000.

Geometrical Analysis of Average Pulsar Profiles of PSR B1857-26

Huaxiang Wang
Urumqi Astronomical Observatory, NAO, Urumqi 830011
Department of Astronomy, Peking University, Beijing 100871

Applying the Gaussian fit separation of the average profile (GFSAP) method, we examined the mean pulse profile of PSR B1857-27 at five frequencies. This method provides us important insight into the pulsar emission beam structure. As a result, we calculated the opening angles and the emission altitudes. The spectral difference between different parts of the emission region is apparent. Benefiting from the separation, we are able to discuss the geometric properties of the three emission zones: the core, the inner cone and the outer cone.

New Method for Magnetic Inclination Angle of Pulsar

Xuanbin Xu
Department of Astronomy, Peking University, Beijing 100871

Magnetic inclination angle is not only a basic parameter of pulsar, but also a key parameter of polar cap model. There still have no perfect method to estimate this parameter now. Several authoritative methods all need good polarization measurement and profile datum. But in more than 1000 pulsars, there is only a few part according it. It is great important how to expand the sample of magnetic inclination angle for numerous theoretic and statistical research subject. This paper first introduction several methods of estimating magnetic inclination angle; and we analysis the polarization measurement of pulsars; then we develop our new method. This method is based on the classification of profile and the distribution of Q parameter for different class pulsars, and it is applicable for those with bad linear polarization measurement but good classification pulsars.

Radio jet in AGNs

D.R. Jiang, X.Y. Hong and Xinwu Cao
Shanghai Astronomy Observatory

The talk present the some results about the study of the radio jets in AGNs in Shanghai Observatory group. The VLBI observations shown the supperluminal motion, the bending, and probable rotation of the jets in some AGNs, the relationship between the structure variation of the jet and the total flux density variation is discussed. The multiband and multi-epoch VLBI observation of a sub-sample EGRET sources shown there are some EGRET AGNs have a symmetric structure at VLA scale, it is non consistent with the general idea that the EGRET AGNs are strong beamed. The preliminary results of 7 intermediate BL Lac objects (IBLs) suggested that the IBLs have the similar jet structure with the RBLs (IBLs). We will briefly discuss the links between the radio jet and the central engine.

Black hole masses and radio properties of Active Galactic Nuclei

Xue-Bing Wu{1}, J.L. Han{2}, F.K. Liu{1}, T.Z. Zhang{1}

  1. Department of Astronomy, Peking University, Beijing 100871, China
  2. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
Supermassive black hole (SMBH) is believed to be an essential part of AGN activities. Recently a lot of dynamical measurements made by the HST have shown that many nearby galaxies host SMBHs with mass of 10^6 to 10^9 solar mass. Reverberation mapping of about 40 AGNs also revealed that such SMBHs exist in AGNs. There is a tight relation between SMBH masses and central velocity dispersions for both nearby and active galaxies. Using this relation we can reliably estimate the SMBH masses of a lot of AGNs for which other mass measurement techniques can not apply. For a sample of Seyfert galaxies, we found that the radio power increase with SMBH masses, similar as that found for quasars and nearby galaxies. However, AGNs have 100 times or more radio power than that of nearby galaxies at the given black hole mass. For radio-loud AGNs, the nuclear radio-loudness tends to increase with SMBH mass. This suggests that some extremely radio-loud AGNs may have largest SMBH masses. No relation between the nuclear radio-loudness and SMBH mass has been found for radio-quiet AGNs. We also estimated the SMBH masses and the Eddington ratios (L/L_Edd) for a sample of AGNs with elliptical host galaxies and found that radio-loud AGNs may have lower Eddington ratios than radio-quiet AGNs. Some related physics on black hole accretion disks and jet formation mechanisms are discussed.

Parsec-Scale Rotation-Measure Distribution in 3C147 at 3.6 cm

Haiyan Zhang

VLBA polarization observations of the steep-spectrum quasar 3C147 were made at four frequencies in the available 8 GHz band. The distribution of the rotation measure of this source was detected, which makes it possible to remove the Faraday screen pixel-by pixel and obtain the intrinsic magnetic field structure of the source.

VLBI observations of the quasar 0202+149 on scales from 0.5 mas to 0.5 arc

Weihua Wang
Shanghai Astronomy Obervatory

Not available yet!

Thomson scattering effect on compact symmetric radio source OQ208

Xiang Liu
NAOC, Urumqi

The effect of Thomson scattering in broad line radio galaxy OQ208 was investigated, it could account for the large flux ratio of lobes in OQ208. And the effect for other sources, e.g. NGC4261 is also discussed.

Detection of intrahour variations in quasar 3c273?

Xiang Liu
NAOC, Urumqi

A kind of quasi-periodic intrahour radio variations pointing bright quasar 3c273 were detected at 6cm and 3.6cm bands using Urumqi 25meter radio telescope. We may estimate a size around the accretion disk of the quasar if the detected variations are intrinsic and outburst from the center.

The beaming mode for superluminal radio sources

J.H. Fan
Center for Astrophysics, Guangzhou University, Guangzhou 510400, China;
National Astronomical Observatory, CAS, Beijing, China;
CAS-PKU Astrophysics Center, Beijing, China.

Relativistic beaming model has been successfully used to explain the observational properties in active galactic nuclei (AGNs). In this model the emissions are composed of two compnents, namely, the boosted and the isotropic ones. But how much is from each part is unknown. It is proposed that the luminosity in the jet is proportional to the unbeamed one in the comoving frame, i.e., f=(L_{jet})/(L_{ub}). However, the value of the ratio, f is not easy to determine. In this paper, we used the beaming model and the radio sources with superluminal motions (SM) to estimate the ratio for each source. log f = -2 to 3 is found.

The periodicity analysis of the radio loud blazars

R.G. Lin, J.H. Fan
Center for Astrophysics, Guangzhou University, Guangzhou 510400, China

Based on the radio data observed with the radio telescope in Michegon University. Periodicity analysis was done using the Jurkevich method. To discard the false period caused by the data distribution, Montel Carlo method is also used in the analysis.

Highly polarized radio sources

JinLin Han

Not available yet!

Radio dichotomy of X-ray-selected AGNs

JiangHua Wu

Quasars and AGNs are traditionally devided as radio-loud and radio-quiet. Optically selected AGN samples usually show bimodal distributions in radio-loudness. But recent radio selected AGN sample (the FIRST Bright Quasar Survey) does not show this radio dichotomy and tends to find radio-intermediate AGNs. Allowing for the apparent selection effects in optically and radio selected AGN samples, here we use an X-ray selected sample to readdress this question.

Jet formation and blazar evolutionary sequence

Xinwu Cao
Shanghai Astronomy Observatory

I review the recent progresses on the theories of jet formation. The relative importance of the different jet acceleration mechanisms are compared. The physical implications on the blazar evolutionary sequences are discussed.

Radio Supernovae

Zongwei Li
Astronomy Department, Beijing Normal University

Not available yet!

Searching candidates of supernova remnant using radio survey data

X.Z. Zhang
National Astronomical Observatories, CAS, Beijing 100012,China
The MPIfR-CAS Group, Beijing 100012, China

A supernova remnant (SNR) usually consists of extended nonthermal radio emission. Most of them show shell or partial shell structure, with an average spectral index of $\alpha\sim -0.45 $ ($S \propto \nu^{\alpha}$). Because the emission is produced by synchrotron process, it is usually (partially) polarized at short wavelengths, though according to the Green catalog (2000), most SNRs have a low degree of polarization at longer wavelengths. In a search using NVSS data, Zhang et al. (2002) have found some candidate Galactic radio sources,G41.9+0.04,G47.8+2.03, G74.8+0.63, and G93.2+2.63, with shell structure, nonthermal spectrum, weak polarization, and no strong infrared emission associated. In this contribution results of these four candidates are reported.

AIRE Plan in Tsinghua University

Jianfeng Zhou
Tsing Hua University

One big challenge that modern astrophysicists should face is how to use Terabytes (maybe Perabytes soon) of astrophysical database effectively. The proposed AIRE (Astrophysical Integrated Research Environment) plan is to help astrophysicists solve this problem. The AIRE is divided into three main parts. The first part is automatic data searching and saving system. After one user input his/her interested target, AIRE will automatically search and download all kinds of relevant data (such as image, spectrum, lightcurve etc. ...) from tens of web sites around the world. For some frequently used data, AIRE can preserve a local copy. The second part is web-based astrophysical data processing platform. Commonly used software like AIPS, DIFMAP, IRAF, HEASOFT, CIAO, IDL, MATLAB, OCTAVE etc. will be installed in central server. Just need a web browser, astrophysicists in different places, using different computers and operating system can process the data in the server. The third part is a concurrent project system (CPS). Under the help of CPS, astrophysicists in different fields can pursue a collaborative reserch efficiently.

Pulsar scintillation - probe of the interstellar medium

W. Sieber
Hochschule Niederrhein, University of Applied Sciences
Krefeld, Germany

It became clear shortly after the detection of pulsars in 1967 that the intensity variations which are characteristic for pulsar radio emission are at least partly due to scintillation in the interstellar medium. Pulsars belong obviously to one of the two classes of celestial radio emitters whose emission regions are compact enough -defined in this case by the magnetosphere of the neutron star - to show scintillation; some active cores of galaxies building another class. The pulsed character of the emission of pulsars allows in addition to determine the dispersion measure, i.e. the integrated content of electrons along the line-of-sight to the source. This gives the possibility to estimate individually the distance to each pulsar once a model of the distribution of electrons in the Galaxy is known. Since both, the scintillation and the dispersion measure, refer to the same thermal electrons, pulsars are ideal probes of the turbulent electron component of the interstellar medium. Moreover, these electrons cause Faraday rotation along the line-of-sight in the presence of magnetic fields, giving clearly measurably effects in the case of the often highly linearly polarised emission of pulsars. Pulsars open up, therefore, the possibility to investigate the electron component of the interstellar medium, especially its random density variations and thereby the turbulence spectrum in parameter ranges, inaccessible to other observations. The paper will show, what kind of measurements have succeeded so far to analyse the turbulence spectrum, what parameter ranges have been covered, what kinds of models have been discussed and in what directions further investigations will go.

Theoretical Refractive Scintillation Simulations of Pulsars

Ai-zhi Zhou et al.
Department of Astronomy, Peking University, Beijing 100871

Using the refractive interstellar scintillation theory, we simulate the theoretical structure functions for both the Kolmogorov spectrum and the super-Kolmogorov spectrum of five pulsars at 610MHz and compare them with the observations. The theoretical results for accord with the observations very well. This indicates that the flux density variations observed for these pulsars are due to a propagation effect-refractive scintillation-not to intrinsic variability. It provides some evidence supporting the RISS theory and the extended medium model and some information about the local interstellar scattering medium (LISM). And it also gives some theoretical proof of the refinements of the models.

Evidence of geodetic precession in timing observation of binary pulsar PSR B1534+12

Biping Gong
Nanjing University

Not available yet!

Evolution of pulsar scale-height

Xiaohui Sun

Not available yet!

Viewpoints of China on Millisecond Pulsar Timing

Ni Guangren Ke Xizheng
National Time Service Center, CAS, Xi'an 710600

Recent research results of pulsar timing in the world are introduced. Then the developments and viewpoints of pulsar timing research in China are summerized. It is thought that the time scale of millisecond pulsar is possible to be set up, and that pulsar time and atomic time can be contrasted and verified by each other and developed side by side. Long-term stability of the ensemble pulsar time is obviously better than that of atomic time. In time scale research, the method of wavelet analysis is superior to the conventional ones. Finally international cooperation is suggested and the prospects of development layout of pulsar time are presented.

Simulation of pulsar distribution in our Galaxy

Yingchun Wei
NAOC, Urumqi

Not available yet!

Quark Matter and Strange Stars

R. X. Xu
Astronomy Department, Peking University

The properties of quark-gluon-plasma (QGP) in the standard model of particle physics are briefly reviewed. It should be a great chance to study the quantum chromodynamical (QCD) nature of strong interaction if we can have direct experiments or observations of QGP. Beside the effort of creating quark matter in the relativistic collisions of heavy ions, an astrophysical way to study QGP is to identify strange quark matter (SQM, a kind of QGP with near equal numbers of light quarks) as the residual after core-collapse type supernova explosion. Such quark stars are simply called to be strange stars. Possible methods to distinguish neutron stars and strange stars are presented.