射电望远镜的发展和前景

在近代科学技术发展的基础上诞生和成长起来的射电天文学已经走过了66年的历程,作为射电天文学主要探测工具的射电望远镜有了长足的进步,面临21世纪人类社会和自然科学技术包括天文学发展的挑战,射电望远镜及射电天文学将迈出新的步伐．从射电天文学和射电望远镜发展的关系、射电望远镜几个主要发展方向和目前水平、自90年代以来逐步勾画而明确起来的未来发展方向等方面阐明了射电望远镜的发展和前景,以作为我国发展新一代射电望远镜的参考．     

Correlation between the Directions of the Magnetic Fields and Major Axes of Extragalactic Radio Sources

The distribution of relative position angles between the integrated intrinsic polarization (perpendicular to the direction of the intrinsic magnetic field) and the major axis of an extragalactic radio source were studied for different types of radio sources. Data for 280 extragalactic radio sources were used and it was found that there are large differences in the relative orientation of different types of radio sources. The directions of the intrinsic integrated magnetic fields correlate with the major radio axes of more elongated radio sources (K > 2.5, where K is the ratio of lengths of the major and minor axes of the radio images) and for radio sources of type FR II, whereas for less elongated objects (K < 2.5) and for radio sources of type FR I the magnetic fields do not correlate at all with the radio axes. An alternative mechanism for the formation of a radio galaxy from relativistic plasma ejected from the central part of an optical galaxy and moving in its large-scale, dipole magnetic field may be a theoretical basis for classification with respect to the elongation parameter K of the radio image.     

Ellipticity of Nearby Elliptical Galaxies Identified with Extended Extragalactic Radio Sources

The dependence of the ellipticity of nearby optical galaxies associated with extragalactic radio sources on the type of radio galaxy is considered. It is shown that elliptical galaxies identified with radio galaxies of the FRI type and with radio sources having a radio image with a small elongation have a smaller ellipticity, on the average, than those associated with radio galaxies of the FRII type and with radio sources with greater elongation. As one possible explanation for this phenomenon, one can assume that the optical galaxies associated with radio galaxies of type FRI and with radio sources of small elongation are oriented in space so that they are observed edge-on relatively rarely.     

A complex solar radio burst and the characteristics of its related microwave sources and EUV coronal loops

On 2001 Oct. 19, a very complex solar radio burst with a host of interesting features was observed with a broadband (0.7–7.6 GHz) solar radio spectrometer. Combining with the data of NoRH (Nobeyama Radio Heliograph) and TRACE (Transition Region and Corona Explorer), the spectral features of the radio burst, the evolution of the microwave radio sources, and relations with the complex EUV coronal loops are analyzed. The burst is the radio manifestation of a large double-ribbon flare; it consisted of two stages. The earlier stage was dominated bya broadband burst in the centimeter-meter waveband from gyro-synchrotron emission of sources at the footpoints of the loop. The later stage was dominated by a narrow-band decimeter wave burst in the decimetermeter waveband, from a combination of plasma emission and gyro-resonance emission from sources in the top of the loop.     

Trying to enlarge the sky coverage of the FAST

The proposed FAST project is a novel giant spherical radio telescope, with active elements which form a temporary paraboloid to track radio objects in the sky. Efforts have been made to extend the limited sky coverage that is a characteristic disadvantage of Arecibo-style radio telescopes. Three measures under investigation are introduced in this paper. The expected performance of the telescope is described, and a brief comparison is made with some of the largest existing radio telescopes. This revised version was published online in July 2006 with corrections to the Cover Date.     

三厘米波段太阳射电爆发中的短时标精细结构

在1989年3月至1990年4月间,我们对太阳射电辐射进行快速采样观测.发现三厘米波段射电爆发亦具有快速精细结构,时标尺度在0.1至2秒间。     

On the formation of cluster radio relics

In several merging clusters of galaxies so-called cluster radio relics have been observed. These are extended radio sources which do not seem to be associated with any radio galaxies. Two competing physical mechanisms to accelerate the radio-emitting electrons have been proposed: (i) diffusive shock acceleration and (ii) adiabatic compression of fossil radio plasma by merger shock waves. Here the second scenario is investigated. We present detailed three-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon filled with turbulent magnetic fields through a shock wave. Taking into account synchrotron, inverse Compton and adiabatic energy losses and gains, we evolved the relativistic electron population to produce synthetic polarization radio maps. On contact with the shock wave the radio cocoons are first compressed and finally torn into filamentary structures, as is observed in several cluster radio relics. In the synthetic radio maps the electric polarization vectors are mostly perpendicular to the filamentary radio structures. If the magnetic field inside the cocoon is not too strong, the initially spherical radio cocoon is transformed into a torus after the passage of the shock wave. Very recent, high-resolution radio maps of cluster radio relics seem to exhibit such toroidal geometries in some cases. This supports the hypothesis that cluster radio relics are fossil radio cocoons that have been revived by a shock wave. For a late-stage relic the ratio of its global diameter to the filament diameter should correlate with the shock strength. Finally, we argue that the total radio polarization of a radio relic should be well correlated with the three-dimensional orientation of the shock wave that produced the relic.     

Location of Decimetric Pulsations in Solar Flares

This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30?–?240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source.     

The Location of the Nucleus of NGC 1068 from HST Imaging Polarimetry and Absolute Astrometry

We present the results of a program to obtain an accurate (better than 100 mas) astrometry of HST images of NGC 1068 and consequently a direct registration with radio images. The optical peak seen in the HST images is located at α = 02h42m40.711s, δ = -00°00′47.81 (J2000, FK5), with an error of 80 mas. The hidden nucleus, as determined by HST imaging polarimetry, falls at α = 02h42m40.710s, δ = -00°00′48.11. It is offset toward the South, i.e. along the radio axis, with respect to the inverted spectrum radio component, S1, by 170 mas (12 pc). This does not rule out that S1 is indeed associated with the obscuring torus and the central engine, but suggests that the nucleus of NGC 1068 might be radio silent or its emission absorbed also at radio wavelengths. An anti-correlation between radio and optical emission is revealed; the radio jet lies on a region of relatively low optical emission and is surrounded by line-emitting clouds. These results can be understood as due the interaction between the jet and the surrounding medium. The outflowing plasma is sweeping and heating the interstellar gas causing the line-emission to be highly enhanced along the edges of the radio jet. It appears that the morphology of the Narrow Line Region of NGC 1068 is dominated by the presence of a radio outflow, as already revealed by HST observations of several Seyfert galaxies with extended radio emission. This revised version was published online in July 2006 with corrections to the Cover Date.     

An atlas of predicted exotic gravitational lenses

We present an investigation of the relationships between the radio properties of a giant radio galaxy MRC B0319−454 and the surrounding galaxy distribution with the aim of examining the influence of intergalactic gas and gravity associated with the large-scale structure on the evolution in the radio morphology. Our new radio continuum observations of the radio source, with high surface brightness sensitivity, images the asymmetries in the megaparsec-scale radio structure in total intensity and polarization. We compare these with the three-dimensional galaxy distribution derived from galaxy redshift surveys. Galaxy density gradients are observed along and perpendicular to the radio axis: the large-scale structure is consistent with a model wherein the galaxies trace the ambient intergalactic gas and the evolution of the radio structures are ram-pressure limited by this associated gas. Additionally, we have modelled the off-axis evolution of the south-west radio lobe as deflection of a buoyant jet backflow by a transverse gravitational field: the model is plausible if entrainment is small. The case study presented here is a demonstration that giant radio galaxies may be useful probes of the warm-hot intergalactic medium believed to be associated with moderately over dense galaxy distributions.     

Galaxy shells and the structure of radio galaxies: Clues from Centaurus A (NGC 5128)

We show that the northern middle radio lobe of Cen A, an intriguing and much debated manifestation of radio lobe asymmetry, can be understood in terms of a direct interaction of the northern jet with a gaseous cloud associated with a stellar shell. This same basic mechanism was proposed earlier for the northern inner lobe, but new data allows a more detailed case to be made for the northern middle lobe. Although such an interaction can presently be demonstrated only for Cen A, the nearest radio galaxy, it is likely to be a fairly common occurrence and it provides an alternative to models invoking episodic nuclear activity, possibly accompanied with jet precession, for radio galaxies with multiple lobes and S-shapes. This proposed scenario may also play a key role in the origin of prominent radio galaxy morphological classes, such as the Wide-Angle-Tail sources and the Z-symmetric X-shaped radio sources. The strong tendency for radio lobes to be more distorted in double radio sources with jets that are in closer alignment with the optical major axis of the host elliptical galaxy can likewise be understood in terms of jet–shell interactions. In the frequent cases when jet activity is triggered by mergers of a large elliptical galaxy with a disk galaxy containing cold gas the impact of the gas associated with stellar shells upon the jets is likely to have significant manifestations.     

Radio galaxies with signatures of merging from the list of giant radio galaxy candidates based on NVSS data

Eight radio sources with signatures of interacting galaxies have been detected within the framework of the project aimed at expanding the list of giant radio galaxies based on NVSS data. The objects have a nontrivial structure in the radio band: four sources exhibit an S-shape, three sources exhibit an X-shape typical of sources at the final stage of radio galaxy merging, and one radio galaxy has a double nucleus. Using the CATS, NED, and SkyView databases, we have made the optical and radio identifications of these objects and constructed their continuum radio spectra.     

日食的射电观测(英)

日食为射电天文提供了一维高空间分辨率太阳射电观测机会．日食射电观测在太阳射电物理的发展上起过重要的作用．文中对日食射电观测的若干重要因素作了介绍和分析．日食射电观测在我国太阳射电天文发展上也起了重要作用．文中简要介绍了在我国组织观测的1958年、1968年、1980年及1987年的太阳射电日食观测及其主要结果．     

A sample of radio-loud active galactic nuclei in the Sloan Digital Sky Survey

A sample of 2712 radio-luminous galaxies is defined from the second data release of the Sloan Digital Sky Survey (SDSS) by cross-comparing the main spectroscopic galaxy sample with two radio surveys: the National Radio Astronomy Observatories (NRAO) Very Large Array (VLA) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey. The comparison is carried out in a multistage process and makes optimal use of both radio surveys by exploiting the sensitivity of the NVSS to extended and multicomponent radio sources in addition to the high angular resolution of the FIRST images. A radio source sample with 95 per cent completeness and 98.9 per cent reliability is achieved, far better than would be possible for this sample if only one of the surveys was used. The radio source sample is then divided into two classes: radio-loud active galactic nuclei (AGN) and galaxies in which the radio emission is dominated by star formation. The division is based on the location of a galaxy in the plane of 4000-Å break strength versus radio luminosity per unit stellar mass and provides a sample of 2215 radio-loud AGN and 497 star-forming galaxies brighter than 5 mJy at 1.4 GHz. A full catalogue of positions and radio properties is provided for these sources. The local radio luminosity function is then derived both for radio-loud AGN and for star-forming galaxies and is found to be in agreement with previous studies. By using the radio to far-infrared (FIR) correlation, the radio luminosity function of star-forming galaxies is also compared to the luminosity function derived in the FIR. It is found to agree well at high luminosities but less so at lower luminosities, confirming that the linearity of the radio to FIR correlation breaks down below about 10²² W Hz⁻¹ at 1.4 GHz.     

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

We present a, large complex radio burst and its associated fast tune structures observed on 2001 April 10 in the frequency range of 0.65-7.6 GHz. 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' re-connection 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).     

星系团的射电研究进展

我们从四个方面综述星系闭的射电研究进展。首先介绍了星系闭中的分立射电源，特别是ｃＤ星系研究的一些最新进展和结果。继而介绍了星系闭中射电晕的分类、目前的观测结果和理论解释。星闭中的磁场主要由射电研究得出，在本文中对此也作了适当的介绍和讨论。最后还简介了在星系闭射观测中发现的ｒｅｌｉｃ射电源。     

Luminosity Functions of Quasars and Seyfert Galaxies

The optical luminosities of extragalactic objects with broad emission lines, i.e. quasi-stellar radio sources, radio quiet quasi-stellar objects and Seyfert galaxies are compared. At high luminosities (M < - 23) we find no difference in the form of the optical luminosity function for radio quiet and radio emitting objects; at low luminosities this function is growing steeply only for radio quiet objects, whereas for objects with higher radio indices it remains nearly constant below M = - 22. This may possibly be interpreted as indicating a division between the optically bright “quasars” and the less luminous objects. The quasars with the highest radio index show only a small scatter in optical luminosities and thus yield a well defined Hubble relation.     

Radio galaxies with a 'double-double morphology'– I. Analysis of the radio properties and evidence for interrupted activity in active galactic nuclei

We present four Mpc-sized radio galaxies which consist of a pair of double-lobed radio sources, aligned along the same axis, and with a coinciding radio core. We call these peculiar radio sources 'double-double' radio galaxies (DDRGs) and propose a general definition of such sources: a 'double-double' radio galaxy consists of a pair of double radio sources with a common centre. Furthermore, the two lobes of the inner radio source must have a clearly extended, edge-brightened radio morphology. Adopting this definition, we find several other candidate DDRGs in the literature. We find that in all sources the smaller (inner) pair of radio lobes is less luminous than the larger (outer) pair, and that the ratio of 1.4-GHz flux density of these two pairs appears to be anticorrelated with the projected linear size of the inner source. Also, the outer radio structures are large, exceeding 700 kpc. We discuss possible formation scenarios of the DDRGs, and we conclude that an interruption of the jet-forming central activity is the most likely mechanism. For one of our sources (B 1834+620) we have been able observationally to constrain the length of time of the interruption to a few Myr. We discuss several scenarios for the cause of the interruption, and suggest multiple encounters between interacting galaxies as a possibility. Finally, we discuss whether such interruptions help the formation of extremely large radio sources.     

Orientation of extragalactic radio sources relative to the elliptical galaxies associated with them

The relative orientations of the optical and radio axes of radio galaxies are analyzed using data for 271 objects. It is found that the radio axes correlate with the minor axes of the optical galaxies for more elongated radio galaxies (K > 2.5, where K is the ratio of the lengths of the major and minor axes of the radio image) and for radio galaxies of the class FRII, whereas for less elongated radio galaxies (K < 2.5) and radio galaxies of the class FRI the radio axes correlate with the major axes of the optical galaxy. In both cases the correlation turns out to be more significant when the radio galaxies are classified in terms of their elongation than when they are classified in terms of the Fanaroff-Riley criterion. The classification in terms of elongation of the radio image can therefore be of interest for understanding overall problems associated with the mechanism of formation and evolution of radio galaxies. A theoretical foundation for such a classification may be the alternative mechanism of formation of radio galaxies from relativistic plasma ejected from the central part of the optical galaxy and moving in its large-scale, dipole magnetic field. Translated from Astrofizika, Vol. 42, No. 3, pp. 365–371, July–September, 1999.