用于雷达天文研究的高速基带数据记录系统

为了开展雷达天文科学研究, 将射电望远镜接收的雷达回波信号进行采集和记录, 研究基于SNAP (Smart Network ADC (Analog to Digital Converter) Processor)硬件实验板和快速存储服务器设计并开发了雷达天文基带数据采集与记录系统. 该系统采用CASPER (Collaboration for Astronomy Signal Processing and Electronics Research)提供的图形化FPGA (Field Programmable Gate Array)开发工具流, 设计了双通道、256MHz带宽信号采集和VDIF (VLBI (Very Long Baseline Interferometry) Data Interchange Format)基带数据输出固件程序; 基于HASHPIPE (High Availability SHared PIPeline Engine)多线程管理引擎开发了双万兆以太网口实时基带数据存储程序, 存储带宽达到1GB/s; 最后编写了VDIF格式到雷达天文格式的转换程序. 经过脉冲星信号观测实验检测, 该系统准确、可靠.     

遥测接收机基带信号处理的数字化实现方法

根据VLBI系统中接收的遥测信号基带信号的特点,介绍了利用虚拟无线电技术实现遥测接收机基带信号处理的基本原理,并分别概述了接收机的载波解调、副载波解调、数据转换环3个功能模块的数字化实现方法。仿真结果和实测数据表明,利用虚拟无线电技术能够很好地实现对遥测信号的解调和同步工作,又因该技术本身具有容易更新、方便添加接口、可并行化等优点,这种基于虚拟无线电技术的遥测接收机基带处理系统,将能够为遥测、导航、天线组阵等相关技术提供很好的实验和应用平台。     

A 256 MHz Bandwidth Baseband Receiver/Spectrometer

Wideband untuned baseband receivers incorporating high-resolution digitisers and polyphase digital filter banks (PDFBs) have been proposed for SKA and LOFAR, and PDFBs are being actively developed as core elements of beamformers, spectrometers and cross correlators for a number of other radio telescopes. Early on-air test results of a 1024-channel, 0–256 MHz baseband receiver, demonstrate excellent spectral purity and robustness against strong in-band RFI.     

Radio pulsars with expected gamma radiation and gamma-ray pulsars as pulsating radio emitters

Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz.     

Scalable framework of intelligent RFI flagging for large-scale HI survey data from FAST

Radio frequency interference (RFI) identification is a key step in radio data processing. In order to efficiently process huge volumes of data produced by modern large radio telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST), exceptional balance between accuracy and performance (throughput) is required for RFI flagging algorithms. RFI-Net is a single-process RFI identification package based on deep learning technique, and has achieved a higher flagging accuracy than the classical SumThreshold method. In this paper, we present a scalable RFI flagging toolkit, which can drive parallel workflows on multi-CPU and multi-GPU clusters, with RFI-Net as its core detector. It can automatically schedule the workload and aggregate itself after errors according to the running environment. Moreover, its main components are all pluggable, and can be easily customized according to requirements. The experiments with real data of FAST showed that using eight parallel workflows, the toolkit can process sky survey data at a speed of 66.79 GB/h, which means quasi-real-time RFI flagging can be achieved considering the data rate of FAST extragalactic spectral line observations.     

Discovery of high-velocity EHB stars in the globular cluster ωCentauri(NGC 5139)

We report the discovery of 45 high-velocity extreme horizontal branch(EHB) stars in the globular cluster Omega Centauri(NGC 5139).The tangential velocities of these EHB stars are determined to be in the range 93~313 km s~(-1),with an average uncertainty of ~27 km s~(-1).The central escape velocity of the cluster is determined to be in the range 60~105 km s~(-1).These EHB stars are significantly more concentrated toward the cluster core compared with other cluster members.The formation mechanisms of these EHB stars are discussed.Our conclusions can be summarized as follows:(1) A comparison of the tangential velocities of these EHB stars to the centra]escape velocity of the cluster shows that most if not all of these EHB stars are unbound to the cluster;(2) These EHB stars obtained high velocities in the central cluster region no longer than ~1 Myr ago and may be subsequently ejected from the cluster in the next ~1 Myr;(3) If the progenitors of these EHB stars were single stars,then they may have experienced a fast mass-loss process.If the progenitors were in close binaries,then they may have formed through disruptions by the intermediate-mass black hole in the cluster center.     

Solar radio spectrography in Europe

Recent technical progress of solar radio spectrography is concerned with digital data recording, the achievement of high time and frequency resolution, and with an improved coverage of the radio range at short and long wavelengths. A spatially-distributed network of radio spectrographs allows for complementary information about solar events and periods of activity selected for detailed investigation.By modern radio spectrographs a wealth of not yet adequately classified spectral fine structures can be observed, some of them potentially intimately related to effects of fragmentation of flare energy and/or to processes related to coronal heating. Requirements for the choice of technical parameters of solar spectrographs for checking theoretical models of fundamental processes of energy release are reflected in modern instruments. Prospects for future observations are briefly included.     

New Digital Magnetograph At Big Bear Solar Observatory

A new digital magnetograph system has been installed and tested at Big Bear Solar Observatory. The system uses part of BBSO's existing videomagnetograph (VMG) system: a quarter wave plate, a ferro-electric liquid crystal to switch polarizations, and a 0.25 Å bandpass Zeiss filter tuned at Cai 6103 Å. A new 256×256 pixels, 12-bit Dalsa camera is used as the detector and as the driver to switch the liquid crystal. The data rate of the camera is 90 frames s–1. The camera is interfaced to a Pentium-166 PC with a Tech imaging board for data acquisition and analysis. The computer has 128 MByte of RAM, and up to 700 live images can be stored in memory for quick post-exposure image processing (image selection and alignment). We have significantly improved the sensitivity and spatial resolution over the old BBSO VMG system. In particular: (1) New digital image data are in 12 bits while the video signal is digitized as 8 bits. Polarizations weaker than 1% can not be detected by a single pair subtraction in the video system. The digital system can detect a polarization signal of about 0.3% by a single pair subtraction. (2) Data rate of the digital system is 90 frames s–1, that of the video system is 30 frames s–1. So the time difference between two polarizations is reduced in the new system. Under good seeing conditions, the data rate of 90 frames s–1 ensures that most of the wavefront distortions are frozen and fairly closely the same for the left and right circular polarized image pairs. (3) Magnetograms are constructed after image selection and alignment. We discuss the characteristics of this new system. We present the results of our first tests to reconstruct magnetograms with speckle interferometric techniques. We also present some preliminary results on the comparison of facular/micropore contrasts and magnetic field structure. The experiment with this small detector lays ground for a larger format digital magnetograph system at BBSO, as well as a future Fabry-Pérot system, which will be able to scan across the spectral line.     

Analysis of the RC catalog sample in the region overlapping with the regions of the FIRST and SDSS surveys: I. Identification of sources with the VLSS, TXS, NVSS, FIRST, and GB6 catalogs

Radio sources of the RC catalog produced in 1980–1985 at RATAN-600 radio telescope based on a deep survey of a sky strip centered on the declination of the SS433 source are optically identified in the region overlapping with FIRST and SDSS surveys (about 132?° large). The NVSS catalog was used as the reference catalog for refining the coordinates of the radio sources. The morphology is found for about 75% of the objects of the sample and the ratio of single, double and multicomponent radio sources is computed based on FIRST radio maps. The 74, 365, 1400, and 4850MHz data of the VLSS, TXS, NVSS, FIRST, and GB6 catalogs are used to analyze the shape of the spectra.     

Polarization measurements of solar type III radio bursts at 25.3 MHz

We report the results of 1966, 1968, and 1969 polarization measurements of solar type III radio noise bursts made by recording the output of two orthogonally polarized receiving channels and subsequent digital processing of selected data. The processed data yield total intensity, degree of polarization, ellipticity, and polarization ellipse orientation at 1 second intervals. The measurements are made in a 100 Hz bandwith to minimize the influence of the propagating medium on the measurements. The mean degree of polarization was found to be about 65% in contrast to previous studies which indicated that type III events were more weakly polarized. By assuming that type III bursts are flare related we study the polarization characteristics of type III bursts as a function of the solar longitude of the related flares. The relation between type III event polarization characteristics and flare importance is also investigated. The significance of polarization measurements in studies of solar radio events is pointed out and suggestions for further theoretical research are given.     

In search of infall motion in molecular clumps Ⅱ: HCO~+(1-0) and HCN(1-0)observations toward a sub-sample of infall candidates

Gravitational accretion accumulates the original mass.This process is crucial for us to understand the initial phases of star formation.Using the specific infall profiles in optically thick and thin lines,we searched the clumps with infall motion from the Milky Way Imaging Scroll Painting(MWISP) CO data in previous work.In this study,we selected 133 sources as a sub-sample for further research and identification.The excitation temperatures of these sources are between 7.0 and 38.5 K,while the H_2 column densities are between 10~(21) and 10~(23) cm~(-2).We have observed optically thick lines HCO~+(1-0) and HCN(1-0) using the DLH 13.7-m telescope,and found 56 sources with a blue profile and no red profile in these two lines,which are likely to have infall motions,with a detection rate of 42%.This suggests that using CO data to restrict the sample can effectively improve the infall detection rate.Among these confirmed infall sources are 43 associated with Class O/I young stellar objects(YSOs),and 13 which are not.These 13 sources are probably associated with the sources in the earlier evolutionary stage.In comparison,the confirmed sources that are associated with Class O/I YSOs have higher excitation temperatures and column densities,while the other sources are colder and have lower column densities.Most infall velocities of the sources that we confirmed are between 10~(-1) to 10~0 km s~(-1),which is consistent with previous studies.     

The digital multi-channel radiospectrograph in Nançay

We describe the new Solar Radio Spectrograph which has been operated at the Nançay Radio Astronomy Station since December 1978 for the analog part (which uses photographic film data acquisition) and since July 1979 using digital magnetic recording. This instrument was designed and built by the Space Research Department of the Paris Observatory and covers the range 469–110 MHz.The multichannel receiver yields a high sensitivity, as compared to a sweep-frequency receiver and the frequency windows where external interference is present can be eliminated from the data acquisition.The digital recording leads to convenient intensity calibration procedures and allows a modern data-handling over a large dynamic range: 50 dB with a 11 bit resolution.Intermodulation effects due to non linearities have been kept to a minimum by building the multiplexer as a tree and distributing the amplification along.The time resolution allows the data to be acquired at a rate of 100 samples per second per frequency channel. The frequency resolution can take two values: 120 channels 1 MHz-wide and 100 channels 200 kHz-wide can be positioned anywhere in the range 110–469 MHz.Some observations are shown including type V and type II-like bursts and harmonically related emission in hook structures. Some future plans are briefly mentioned aiming to perform circular polarization measurements in 120 frequency channels and real time data compression.Also at Department of Physics and Electronics, University of Athens, Greece.     

基于Dask并行加速的射电干涉成像网格化方法实现

快速傅里叶变换(Fast Fourier Transform,FFT)比傅里叶变换有更好的算法性能,是射电干涉成像的基础算法,但因为天线阵列的不规则采样,需使用网格化算法将可见度数据重采样到规则的网格上才能应用。基于卷积的网格化计算具有密集型和迭代型的特点,特别是处理海量可见度数据的情况下,高性能的网格化计算对整个成像过程加速尤为重要。为了缓解数据处理的压力,在现有处理整块数据和支持多核计算的算法基础上,拓展应用Dask并行计算框架,不仅将数据分块并分配到多线程上,提高数值计算效率,而且动态的分布式任务调度策略优化了网格化的实时处理。实验结果表明,多核中央处理器利用率显著提高,即使增加数据量,也能进一步提高网格化算法的性能。分布式任务调度能够将单(多)测量集的网格化弹性缩放到单(多)机系统,充分发挥集群的规模化优势。     

Discovery of radio-loud quasars with z=4.72 and z=4.010

We report the discovery of two radio-loud quasars with redshifts greater than 4: GB1428+4217, with z =4.72, and GB1713+2148 with z =4.01. This doubles the number of published radio-selected quasars with z >4, bringing the total to 4. GB1428+4217 is the third most distant quasar known and the highest redshift radio and X-ray source currently known. It has a radio flux density at 5 GHz of 259±31 mJy and an optical magnitude of R ∼20.9. The rest frame absolute UV magnitude, M_v (1450 Å), is −26.7, similar to that of the archetypal radio-selected quasar 3C273 [ z =0.158; M_v (1450 Å)=−26.4]. GB1428+4217 is tentatively detected in ROSAT PSPC observations, which has been confirmed by more recent ROSAT observations described in a companion paper by Fabian et al. Both quasars were discovered during the CCD imaging phase of an investigation into the evolution of the space density of radio-loud quasars at high redshift. Combined with our earlier survey results, these objects give a lower limit on the space density of quasars with radio power P _{5 GHz}>5.8×10²⁶ W Hz⁻¹ sr⁻¹ between z =4 and z =5 of 1.4±0.9×10⁻¹⁰ Mpc⁻³. This can be compared to 2.9±0.2×10⁻¹⁰ Mpc⁻³ at z =2 from Dunlop & Peacock for flat-spectrum sources of the same luminosity.     

High-precision timing of PSR J1600−3053

We present the results of a high-precision timing campaign directed at the binary millisecond pulsar J1600−3053. Submicrosecond pulsar timing has long been the domain of bright, low dispersion measure millisecond pulsars or large diameter telescopes. This experiment, conducted using the Parkes radio telescope in New South Wales, Australia, and utilizing the latest baseband recording hardware, has allowed this pulsar, although distant and faint, to present residuals to a model of its spin behaviour of 650 ns over a period of more than 2 yr. We have also constrained the orbital inclination via Shapiro delay to be between 59° and 70° to 95 per cent confidence and obtained a scintillation velocity measurement indicating a transverse velocity less than 84 km s⁻¹. This pulsar is demonstrating remarkable stability comparable to, and in most cases improving upon, the very best long-term pulsar timing experiments. If this stability is maintained, the current limits on the energy density of the stochastic gravitational wave background will be reached in four more years.     

太阳米波和分米波Ⅱ型、Ⅲ型射电暴及其精细结构观测研究进展

太阳米波和分米波的射电观测是对太阳爆发过程中耀斑和日冕物质抛射现象研究的重要观测手段。米波和分米波的太阳射电暴以相干等离子体辐射为主导,表现出在时域和频域的多样性和复杂性。其中Ⅱ型射电暴是激波在日冕中运动引起电磁波辐射的结果。在Ⅱ型射电暴方面,首先对米波Ⅱ型射电暴的激波起源问题和米波Ⅱ型射电暴与行星际Ⅱ型射电暴的关系问题进行了讨论;其次,结合Lin-Forbes太阳爆发理论模型对Ⅱ型射电暴的开始时间和起始频率进行讨论:最后,对Ⅱ型射电暴信号中包含的两种射电精细结构,Herringbone结构(即鱼骨结构)和与激波相关的Ⅲ型射电暴也分别进行了讨论。Ⅲ型射电暴是高能电子束在日冕中运动产生电磁波辐射的结果。在Ⅲ型射电暴方面,首先介绍了利用Ⅲ型射电暴对日冕磁场位形和等离子体密度进行研究的具体方法;其次,对利用Ⅲ型射电暴测量日冕温度的最新理论进行介绍;最后,对Ⅲ型射电暴和Ⅱ型射电暴的时间关系、Ⅲ型射电暴和粒子加速以及Ⅲ型射电暴信号中包含的射电精细结构(例如斑马纹、纤维爆发及尖峰辐射)等问题进行讨论并介绍有关的最新研究进展。     

Modelling the first probable two-plane lens system B2114+022: reproducing two compact radio cores A and D

We test possible lensing scenarios of the JVAS system B2114+022, in which two galaxies at different redshifts ('G1' at z ₁=0.3157 and 'G2' at z ₂=0.5883) are found within 2 arcsec of quadruple radio sources. For our investigation, we use possible lensing constraints derived from a wealth of data on the radio sources obtained with VLA, MERLIN, VLBA and EVN as well as HST imaging data on the two galaxies, which were presented recently in Augusto et al. In the present study, we focus on reproducing the widest separated, observationally similar radio components A and D as lensed images. We first treat G2 (which is the more distant one from the geometric centre) as a shear term, and then consider two-plane lensing explicitly including G2's potential at the z ₂ plane as the first case of two-plane lens modelling. Our modelling results not only support the hypothesis that the system includes gravitationally lensed images of a higher-redshift extragalactic object, but they also show that the explicit inclusion of G2's potential at the second lens plane is necessary in order to fit the data with astrophysically plausible galaxy parameters. Finally, we illustrate a natural consequence of a two-plane lens system, namely the prediction of distortion as well as shift and stretching of G2's isophotes by G1's potential, which can in principle be measured by subtracting out G1's light distribution in an image of high signal-to-noise ratio and good angular resolution, especially a multicolour one.     

卡尔曼滤波在VLBI数据处理中的应用

本文探讨卡尔曼滤波技术用于VLBI天体测量和大地测量数据处理的原理和方法;并深入地对Herring等提出的软件系统（SOLVK）进行详细研究,提出一些具体的办法以便应用．然后用1993—1994年的VLBI观测资料,精确计算了几种天文学和地球动力学参数作为例证．     

Limits on Cosmological Parameters from Statistical Investigations of the Ratan-600 and 87GB Surveys

The sky distributions of sources in a RATAN-600 survey and a strip of the 87GB survey have been investigated. The presence of deviations from a Poisson radio source distribution is confirmed. A significant fraction of radio sources are associated with the supercluster-void network, which is composed of regular periodic structures on scales from 30 arcmin to one degree. A comparative study of the distributions and identifications of the RATAN-600 and 87GB surveys is performed. The data from this study are used to set limits on the cosmological parameter qo and the epoch of formation of large scale structures in the Universe.     

Radio emission from the Sy 1.5 galaxy NGC 5033

We present new continuum VLA observations of the nearby Sy 1.5 galaxy NGC 5033, made at 4.9 and 8.4 GHz on 2003 April 8. Combined with VLA archival observations at 1.4- and 4.9-GHz made on 1993 August 7, 1999 August 29 and 1999 October 31, we sample the galaxy radio emission at scales ranging from the nuclear regions (≲100 pc) to the outer regions of the disc (∼40 kpc). The high-resolution VLA images show a core–jet structure for the Sy 1.5 nucleus. While the core has a moderately steep non-thermal radio spectrum ( S _ν∝ν^α; α^4.9_1.5≈−0.4), the inner kpc region shows a steeper spectrum (α^8.4_1.5≈−0.9). This latter spectrum is typical of galaxies where energy losses are high, indicating that the escape rate of cosmic ray electrons in NGC 5033 is low. The nucleus contributes little to the total 1.4-GHz radio power of NGC 5033 and, based on the radio to far-infrared (FIR) relation, it appears that the radio and FIR emission from NGC 5033 are dominated by a starburst that during the last 10 Myr produced stars at a rate of 2.8 M_⊙ yr⁻¹ yielding a supernova (type Ib/c and II) rate of 0.045 yr⁻¹. This supernova rate corresponds to about 1 SN event every 22 yr. Finally, from our deep 8.4-GHz VLA-D image, we suggest the existence of a radio spur in NGC 5033, which could have been due to a hot superbubble formed as a consequence of sequential supernova explosions occurring during the lifetime of a giant molecular cloud.