一种用于同步静止卫星监测的微型VLBI网

针对地球静止轨道（GEO）卫星全天时全天候高精度的监测需求，考虑传统甚长基线干涉（VLBI）测站高成本、高投入和GEO卫星专用观测时段有限等制约条件，研发了简易型VLBI观测系统，并组建了包括上海、都匀和乌鲁木齐三站的微型VLBI网（micro VLBI network，MVN），开展了并置站测试以及对GEO卫星亚太6C的连续监测，并评估了当前MVN的观测能力。结果表明MVN扣除系统差后的单站接收精度为2ns，各基线观测时延拟后残差约几纳秒，GEO目标实测位置精度为百米级（内外符精度分别约100m和400m）。不同于传统VLBI和其他GEO监测手段，MVN还具备全天时、全天候、低造价、易布设及易推广等特点，充分表明了其在GEO卫星监测领域的应用价值。     

The VEGA Venus balloon experiment

In June 1985, two instrumented balloons were placed in the atmosphere of Venus as part of the VEGA mission. Each balloon traveled about 30 percent of the way around the planet at a float altitude near 54 kilometers. In situsensors measured pressure, temperature, vertical wind velocity, cloud particle backscatter, ambient light level, and frequency of lightning. A ground-based network of 20 radio antennas tracked the balloons by very long baseline interferometry (VLBI) techniques to monitor the Venus winds. The history, organization, and principal characteristics of this international balloon experiment are described.     

WMAP extragalactic point sources as potential Space VLBI calibrators

The point source list of the Wilkinson Microwave Anisotropy Probe (WMAP) is a uniform, all-sky catalogue of bright sources with flux density measurements at high (up to 94 GHz) radio frequencies. We investigated the five-year WMAP list to compile a new catalogue of bright and compact extragalactic radio sources to be potentially studied with Very Long Baseline Interferometry at millimeter wavelengths (mm-VLBI) and Space VLBI (SVLBI). After comparing the WMAP data with the existing mm-VLBI catalogues, we sorted out the yet unexplored sources. Using the 41, 61 and 94 GHz WMAP flux densities, we calculated the spectral indices. By collecting optical identifications, lower-frequency radio flux densities and VLBI images from the literature, we created a list of objects which have not been investigated with VLBI at 86 GHz before. With total flux density at least 1 Jy and declination above −40°, we found 37 suitable new targets. It is a nearly 25% addition to the known mm-VLBI sources. Such objects are also potentially useful as phase-reference calibrators for the future Japanese SVLBI mission ASTRO-G at its highest observing frequency (43 GHz). The phase-referencing capability of ASTRO-G would allow long integrations and hence better sensitivity for observing faint target sources close to suitable phase calibrators in the sky.     

A Cosmic Microscope to Probe the Universe from Present to Cosmic Dawn:Dual-element Lowfrequency Space VLBI Observatory

A space-based Very Long Baseline Interferometry (VLBI) program, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Square Kilometre Array, FAST, Arecibo) to image the low radio frequency Universe with the purpose of unraveling the compact structure of cosmic constituents including supermassive black holes and binaries, pulsars, astronomical masers and the underlying source, and exoplanets amongst others. The operational frequency bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission plans to launch two 30-m-diameter radio telescopes into 2 000 km×90 000 km elliptical orbits. The two telescopes can work in flexibly diverse modes. (i) Space-ground VLBI. The maximum space-ground baseline length is about 100 000 km; it provides a high-dynamic-range imaging capacity with unprecedented high resolutions at low frequencies (0.3 mas at 1.67 GHz and 20 mas at 30 MHz) enabling studies of exoplanets and supermassive black hole binaries (which emit nanoHz gravitational waves). (ii) Space-space single-baseline VLBI. This unique baseline enables the detection of flaring hydroxyl masers, and more precise position measurement of pulsars and radio transients at mas level. (iii) Single dish mode, where each telescope can be used to monitor transient bursts and rapidly trigger follow-up VLBI observations. The large space telescope will also contribute in measuring and constraining the total angular power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope offers astronomers the opportunity to conduct novel, frontier science.      

Orbiting VLBI

The technique of Michelson interferometry using synchronized radio telescope systems at great separations is known as Very-Long-Baseline Interferometry (VLBI). The method can be extended to give micro-arc-second angular resolution by using radio telescopes in space. There are no technical barriers, and several classes of conceptual systems can be specified.     

Active galactic nuclei imaging programs of the RadioAstron mission

Imaging relativistic jets in active galactic nuclei (AGN) at angular resolution significantly surpassing that of the ground-based VLBI at centimetre wavelengths is one of the key science objectives of the RadioAstron space-VLBI mission. There are three RadioAstron imaging key science programs that target both nearby radio galaxies and blazars, with one of the programs specifically focusing on polarimetry of the jets. The first images from these programs reach angular resolution of a few tens of microarcseconds and reveal unprecedented details about the jet collimation profile, magnetic field configuration, and Kelvin-Helmholtz instabilities along the flow in some of the most studied AGN (3C 84, BL Lac, 3C 273, S5 0836 + 710). Here we give an overview of the goals and strategy of these three ongoing programs, highlight their early results, and discuss the challenges of space-VLBI imaging.     

A VLBI baseline post-adjustment approach for station velocity estimation in Eurasian continent

Baseline lengths and their time-derivatives among 58 geodetic VLBI stations were fitted by using 4439 observing sessions from the International VLBI Service for Geodesy and Astrometry (IVS). First, the velocities of eight stations in Eurasian continent were set as unknown quantities. Then, two standard global solutions from 3523 IVS sessions and 1110 sessions from database code XA, respectively, were applied prior to all-station coordinates and the non-estimated station velocities. Finally, from the relations among the coordinates, velocities, baseline length and its time-derivative, two types of baseline post-adjustment (BPA) were used to estimate the velocities of the eight stations. We discuss the data processing details, including the effect of different prior values for the stations and the optimal solution.     

The evolution of the central component in SN 1986J

The unusual core-collapse supernova 1986J, in the nearby spiral NGC 891, is the first modern supernova in which evidence of a compact remnant of the supernova has been seen. This evidence comes from recent VLBI images, which show the emergence of a new radio component in the center of the expanding radio shell. The new component shows an inverted radio spectrum contrasting with that of the shell. The new component is likely radio emission associated with the black-hole or neutron star compact remnant of the explosion, which would mark the first direct observational link between a modern supernova and such a compact remnant. We report here on our recent VLBI images at 22 and 5 GHz, as well as on our monitoring of the integrated radio spectrum of SN 1986J. In the 22 GHz image, the central component is marginally resolved.     

Space very long baseline interferometry in China

Space very long baseline interferometry (VLBI) has unique applications in high-resolution imaging of the fine structure of astronomical objects and high-precision astrometry due to the key long space–Earth or space–space baselines beyond the Earth’s diameter. China has been actively involved in the development of space VLBI in recent years. This review briefly summarizes China’s research progress in space VLBI and the future development plan.     

Automated and dynamic scheduling for geodetic VLBI – A simulation study for AuScope and global networks

As we move into the next era of geodetic VLBI, the scheduling process is one focus for improvement in terms of increased flexibility and the ability to react with changing conditions. A range of simulations were conducted to ascertain the impact of scheduling on geodetic results such as Earth Orientation Parameters (EOPs) and station coordinates. The potential capabilities of new automated scheduling modes were also simulated, using the so-called ‘dynamic scheduling’ technique. The primary aim was to improve efficiency for both cost and time without losing geodetic precision, particularly to maximise the uses of the Australian AuScope VLBI array.We show that short breaks in observation will not significantly degrade the results of a typical 24?h experiment, whereas simply shortening observing time degrades precision exponentially. We also confirm the new automated, dynamic scheduling mode is capable of producing the same standard of result as a traditional schedule, with close to real-time flexibility. Further, it is possible to use the dynamic scheduler to augment the 3 station Australian AuScope array and thereby attain EOPs of the current global precision with only intermittent contribution from 2 additional stations. We thus confirm automated, dynamic scheduling bears great potential for flexibility and automation in line with aims for future continuous VLBI operations.     

地基设备布站对空间碎片观测能力的影响分析

建立空间碎片地面观测站时,需要用数值仿真工具对其观测能力进行评估和分析.评估观测站能力的重要指标是测站设备对空间碎片的观测量和可观测频度.先进的设备指标和合适的测站位置能够大大提高观测能力.本文使用STK,PROOF等软件,对不同测站雷达和光学设备的观测能力(过境率和探测率)进行了数值仿真和比较分析,得到了一些初步结论,对于空间碎片监测网的设计有一定的参考作用.      

双站跟踪模式下“嫦娥4号”中继星定轨仿真分析

位于地月平动点的探测器因为较差的观测几何,需要地基USB/UXB与天文VLBI长时间的联合跟踪数据获取稳定精确的轨道。提出了利用中国深空网双站共视跟踪平动点探测器,获取双程、三程测距及VLBI测量数据,解算探测器精确轨道的模式。以"鹊桥"卫星为分析对象,首先评估中国深空网对"鹊桥"的跟踪能力。然后分析不同观测组合模式下的定轨计算精度。结果表明:双站共视约束下,深空站每天对"鹊桥"跟踪弧长大于5 h;使用长于6 h的双站跟踪数据进行定轨,系统差的解算更有利于轨道精度提升;跟踪时长超过2天时,必须在轨道解算的同时估计光压系数,并有望实现优于百米的轨道精度。     

Very low frequency interferometry for the Chang’E-2 project

Very low frequency interferometry among two astronomical experiments has been proposed and accepted for further study for the second phase of China’s lunar exploration programme (the Chang’E Programme), which is envisaged to operate a lander and a rover on the surface of the moon. This experiment is an interferometer experiment in the very low frequency (VLF, f < 15 MHz) regime of radio frequencies with at least degree-level angular resolution. The goals include observing solar storm activities, Coronal Mass Ejections, Auroral Kilometric Radiation, and planetary radiation in the solar system, studying the origin of Cosmic Rays, spectral properties of pulsars, surveying ionized hydrogen in the Galaxy, and exploring coherent radio emissions.     

深空测控网干涉测量系统在“鹊桥”任务中的应用分析

在"嫦娥4号"任务的第一阶段—"鹊桥"阶段,北京航天飞行控制中心利用佳木斯及喀什深空站对"鹊桥"进行了干涉测量观测,获取了实时与事后的高精度测角观测量,有效支持了任务的实施。两深空站需同时完成测控任务,无法交替射电源观测来进行系统差标校,基于此系统采用了长时间隔、在航天器观测前及双站结束后观测射电源的标校方法,在地月转移段、月球至L2转移段、Halo轨道形成段开展了多次干涉测量观测,所获得的时延、时延率结果直接应用于事后联合轨道确定,结果表明:深空网的时延观测精度约为3 ns。     

“嫦娥二号”小行星探测试验定轨计算与分析

嫦娥二号于2012-04-15开展对图塔蒂斯小行星的探测试验,至2012-12-13与图塔蒂斯交会,共飞行243 d,这是我国对小行星的首次探测.因为未安装星载导航设备,CE-2 在小行星探测试验的全过程均基于地基USB（Unified S-Band）与甚长基线干涉测量技术（VLBI,Very Long Baseline Interferometry）测量实现导航.对小行星探测期间的定轨计算及精度分析进行了讨论,对我国新建深空站的测量数据进行了分析.针对交会前最后一次轨道机动后,仅有13 d控后数据的现状,提出了快速轨道重建策略.计算结果表明该策略不仅可以有效改进定轨计算精度,还可以实现轨控速度增量的标定.基于重叠弧段的轨道分析比较表明,单独使用USB长弧数据计算可以获得10 km的定轨精度,综合USB与VLBI数据联合定轨,定轨精度可以提高1倍.     

Multiple-site investigation of the properties of an HF radio channel and the ionosphere using Digital Radio Mondiale broadcasting

The Digital Radio Mondiale (DRM), one of the new digital radio broadcasting standards, has been designed to overcome typical short wave radio channel difficulties, such as the multipath propagation and fast temporal changes of the received signal level, both related to the properties of the ionosphere along the path of propagation. In particular, some of the RF carriers used in the applied COFDM transmission technique serve to estimate the current state of the radio channel to enable the proper demodulation of the received signal.We have been detecting such RF carriers on select frequency channels (standard DRM broadcast) using a network of recording stations located in different parts of Poland in order to collect data on the HF radio channel. We have been also evaluating the usefulness of this procedure in providing information on the current state of the ionosphere in the refraction region between the transmitter and receivers. When the DRM system becomes more widespread, this method can supplement data that comes from the ionosondes, since it does not require much financial resources and the receivers can be easily scattered over a large area. This paper presents a set of experimental data and its analysis.     

在月球背面进行低频射电天文观测的关键技术研究

月球具有足够大的尺寸,能够有效地遮挡来自地球的低频电磁波干扰,因此月球背面是进行低频射电天文观测的最佳场所。本文论述了利用低频射电频谱仪在月球背面进行空间低频射电天文观测的意义,给出了低频射电频谱仪工作原理、科学探测目标和系统组成。研究了低频射电频谱仪的设计,并采用低频射电频谱仪对北京中关村地区空中低频电磁波辐射频谱进行了试验探测,结果表明:低频射电频谱仪能够清晰地探测到0.1~40 MHz频带内的广播电台及授时台等发射的低频电磁波信号。     

RATAN-600 and RadioAstron reveal the neutrino-associated blazar TXS 0506+056 as a typical variable AGN

The possible association with the high-energy neutrino event IceCube-170922A has sparked interest in the blazar TXS 0506+056. We present 72 instantaneous 1–22 GHz spectra measured over the past 20 years with the RATAN-600 telescope and compare them with the results of observations of 700 variable Active Galactic Nuclei (AGN) studied within the same program. The recent radio flare of TXS 0506+056 started from a minimum in 2013 and reached its first peak in December 2017 and a second peak in May-June 2018. This was the third strong radio flare in this source since 1997. The spectrum remains nearly flat during the flares. The spectral shape and variability pattern observed in TXS 0506+056 are typical for variable AGN. RadioAstron Space VLBI observations in 2013–2015 did not detect TXS 0506+056 on space-ground baselines of more than 9 Earth diameters. However, an observation on 23 September 2015 resulted in the detection of interferometric signal on 6 Earth diameter baselines at 18 cm close to the detection limit. We consider the possibility that TXS 0506+056 and other AGN may accelerate relativistic protons more efficiently than electrons. Relativistic protons are necessary to produce both the high-energy neutrinos observed in the IceCube Observatory and the high AGN brightness temperatures implied by the RadioAstron detection. They may also provide the main contribution to the observed synchrotron radiation of parsec-scale AGN jets. This supports the suggestion that relativistic protons may play a much more important part in extragalactic astrophysics than earlier anticipated.     

佘山VLBI站本振系统的性能评定

氢钟是甚长基线干涉仪(VLBI)中的一个关键系统。主要介绍与国际VLBI联测而建立的高质量频率标准的性能及氢钟的联接与技术要求。     

一种用于深空导航定位的新型DOR信标

甚长基线干涉测量(VLBI)是深空探测器导航定位的重要手段之一,深空探测器的VLBI观测通常采用差分单程测距(DOR)信标和双差单程测距(Delta-DOR)测量体制,精确地测量深空探测器相对于河外射电源的角距.相位杂散是影响Delta-DOR测量精度的主要误差源之一,针对这项误差研究了一种基于伪随机噪声调制方式的新型...