The Tianma 65 m radio telescope antenna

The Tianma 65 m radio telescope(TMRT)at Shanghai is a fully steerable single-dish radio telescope in China,operating at centimeter to millimeter wavelengths(1.25 GHz to 50 GHz).This paper presents details on the main specifications,design,performance analysis,testing,and construction of the telescope antenna.The measured total efficiency is better than 50%over the whole elevation angle range,first sidelobe levels are less than−20 dB,antenna system noise temperatures are less than 70 K at 30°elevation angle,and pointing accuracy is less than 3″.The measured and calculated results are in good agreement,verifying the effectiveness of the design and analysis.

The Tianma 65 m radio telescope at Shanghai

The Shanghai Tianma 65 m radio telescope(TMRT)is a large,fully rotatable radio telescope with multiple scientific purposes.The main body of the telescope and four low-frequency receiving systems,including L,C,and S/X bands,were completed between 2008 and 2012.From 2013 to 2017,four high-frequency receiving systems,including Ku,K,Ka,and Q bands,were constructed and their performance was comprehensively tested.There are three main innovations.(1)A fully movable large radio telescope system with advanced performance and complete functions has been built.(2)An advanced,reliable main reflector adjustment system has been completed,overcoming gravity deformation and creating a large antenna with a main reflective surface accuracy of 0.28 mm(root mean square)for any elevation.(3)Five innovative technologies have been developed to achieve high-precision pointing in any direction within 3″.The TMRT has made a crucial contribution to the orbital measurement and positioning of China’s lunar and deep space probes.Significantly enhancing China's ability to participate in international VLBI observations and radio astronomy,this has facilitated a series of achievements in observational radio astronomical research,in areas such as VLBI,spectral lines,and pulsars.

Surface shape detection methods for large radio telescopes

The surface accuracy of a radio telescope is directly related to its operational efficiency and detection sensitivity.This is crucial under high-frequency observation conditions,where surface shape errors need to be controlled to within 1/16 of the working wavelength.In addition,the primary reflector of large radio telescopes is subject to dynamic deformation,caused by factors such as gravity and thermal effects.This paper presents a method for detecting the surface shape of radio telescopes using radio interferometry techniques combined with active reflector adjustment technology.This enables accurate assessment and correction of surface errors,ensuring the electrical performance of the radio telescope.This study investigates the practical applications of high-precision measurement techniques,such as microwave holography,out-of-focus holography,and wavefront distortion methods at the Tianma 65 m radio telescope(TMRT).Furthermore,the study presents the construction method of gravity models at different elevation angles and demonstrates the efficacy of the active reflector model.The results of the measurements indicate that the application of these methods to the TMRT has led to a notable enhancement of the accuracy of the primary reflector and a substantial improvement in efficiency in the Q-band.Through a process of iterative measurements and adjustments,the surface shape error is ultimately reduced to 0.28 mm root mean square(RMS).

An improved non-uniform fast Fourier transform method for radio imaging of coronal mass ejections

Radioheliographs can obtain solar images at high temporal and spatial resolution,with a high dynamic range.These are among the most important instruments for studying solar radio bursts,understanding solar eruption events,and conducting space weather forecasting.This study aims to explore the effective use of radioheliographs for solar observations,specifically for imaging coronal mass ejections(CME),to track their evolution and provide space weather warnings.We have developed an imaging simulation program based on the principle of aperture synthesis imaging,covering the entire data processing flow from antenna configuration to dirty map generation.For grid processing,we propose an improved non-uniform fast Fourier transform(NUFFT)method to provide superior image quality.Using simulated imaging of radio coronal mass ejections,we provide practical recommendations for the performance of radioheliographs.This study provides important support for the validation and calibration of radioheliograph data processing,and is expected to profoundly enhance our understanding of solar activities.

面向FAST的卫星电磁干扰监测技术研究与实现

来自人造卫星的信号是射电天文观测面临的主要射频干扰(radio frequency interference,RFI)之一,这些RFI会将天文信号掩埋,为天文信号的搜寻和分析带来困扰。为了缓减卫星对天文观测的影响,我们在之前的工作中为500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope,FAST)开发了卫星电磁干扰监测软件,主要包括卫星数据库、观测模块和监测模块。近年来随着多个巨型卫星星座的规划发射以及望远镜观测模式的增多,卫星对射电天文观测的影响更为复杂,已有的软件已经不能满足实际的需要。为此,本文在单个卫星干扰分析的基础上提出了卫星星座的干扰评估方法,并对已有监测软件进行了升级,升级后卫星数据库覆盖更多的在轨卫星及星座信息且能够自动化更新,观测模块能够支持更多种观测模式下的卫星过境预测和干扰评估。在实际天文观测中,通过接在FAST接收机上的频谱仪数据对软件的干扰预测结果进行了实验验证,结果证明升级后的软件能够在多种观测模式下预测可能威胁的卫星以及对应的过境时间,为望远镜观测规划的调整、卫星干扰的规避和接收系统的保护提供重要的支撑。

Terrain-influenced wind flow of the Qitai radio telescope site

The wind environment of a site is one of the important factors affecting the observation performance of large aperture and high-performance radio telescopes.Exploring the relationship between the effects of different terrains on wind flow is important to optimize the wind environment of the site.The terrain of the Qitai radio telescope(QTT)site located in east Tianshan Mountains at an elevation of about 1800 m was used to study the wind flow in the adjacent zone of antenna based on numerical simulation.The area from 600m south to 600m north of the antenna is defined as the antenna adjacent zone,and three groups of boundaries with different terrains are set up upstream and downstream,respectively.Since the zone where the antenna is located is a slope terrain,in order to verify the influence of terrain on the wind flow and to clarify the relationship between the influence of boundary terrain on the wind flow,a control group of horizontal terrain is constructed.The simulation results show that the wind flow is mainly influenced by the terrain.The highest elevation of the upstream and downstream boundary terrains affects the basic wind speed.The upstream boundary terrain has a greater impact on wind flow than the downstream boundary terrain.In addition,the wind speed profile index obtained by numerical simulation is smaller than the actual index for the wind from south.Therefore,the wind speed at the upper level(about 100 m)obtained by inversion based on the measured wind speed at the bottom(about 10 m)is also smaller than the actual wind speed.

Atlas of dynamic spectra of fast radio burst FRB 20201124A

Fast radio bursts(FRBs) are highly dispersed millisecond-duration radio bursts,[1,2]of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

FAST所受PMT基站电磁干扰及用频防护方法综述

为确定500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope,FAST)与其周边公众移动通信(Public Mobile Telecommunications,PMT)系统的电磁兼容(electromagnetic compatibility,EMC)特性,本文综合论述了FAST宁静区内中国移动、中国联通和中国电信三大运营商所属PMT基站对其产生的电磁干扰。首先,从射电天文业务的频谱划分谈起,论述了射电天文业务干扰源类型,引出了其运行保护标准,进而针对FAST详细说明了FAST宁静区的用频法规和保护要求;其次,分析了ITU-R建议电波传播预测与干扰分析方法,并通过实地测量验证了该方法的适用性,进一步针对性地分析了PMT基站的电磁辐射传播特性,综合评估了FAST宁静区内PMT基站的干扰情况:FAST宁静区域90.24%的PMT基站在一定程度上均会对FAST产生干扰,而在所选分析条件下,仅有43.14%的数据符合FAST保护要求;最后,针对PMT基站干扰信号的抑制和消除,分析了常用的射电天文射频干扰抑制方法,同时为保障FAST免受PMT基站干扰,从FAST和PMT基站的角度出发论述了可行的用频防护措施,并基于实施难度、经济成本、策略收益和通信质量4类指标建立了防护方法的评估体系,对所提防护方法进行了实例说明。上述研究成果可为保障FAST的安全观测提供技术基础。

The FAST Core Array

The Five-hundred-meter Aperture Spherical Radio Telescope(FAST)Core Array is a proposed extension of FAST,integrating 24 secondary 40-m antennas implanted within 5 km of the FAST site.This original array design will combine the unprecedented sensitivity of FAST with a high angular resolution(4.3"at a frequency of 1.4 GHz),thereby exceeding the capabilities at similar frequencies of next-generation arrays such as the Square Kilometre Array Phase 1 or the next-generation Very Large Array.This article presents the technical specifications of the FAST Core Array,evaluates its potential relatively to existing radio telescope arrays,and describes its expected scientific prospects.The proposed array will be equipped with technologically advanced backend devices,such as real-time signal processing systems.A phased array feed receiver will be mounted on FAST to improve the survey efficiency of the FAST Core Array,whose broad frequency coverage and large field of view(FOV)will be essential to study transient cosmic phenomena such as fast radio bursts and gravitational wave events,to conduct surveys and resolve structures in neutral hydrogen galaxies,to monitor or detect pulsars,and to investigate exoplanetary systems.Finally,the FAST Core Array can strengthen China's major role in the global radio astronomy community,owing to a wide range of potential scientific applications from cosmology to exoplanet science.

FAST运行前后所处电磁环境特性研究

为掌握500 m口径球面射电望远镜(Five-hundred-meters Aperture Spherical radio Telescope,FAST)运行前后周边的电磁环境特性变化,针对FAST主要观测频段的电磁信号进行了观测。基于观测结果,分析了FAST周边电磁环境信号的分布特性:在FAST调试期间,主要以87~108 MHz频段广播信号、117.975~137 MHz航空移动信号、806~960 MHz固定移动信号为主,其中900~1200 MHz频率占用度最高,达到1.8%。FAST运行后,在485~566 MHz、614~640 MHz频段新增广播信号,702~798 MHz频段新增了中国广电5G公众移动通信信号,806~960 MHz频段新增固定、移动信号。同时,受2G基站部署密度提升以及3G和4G信号的接入影响,1710~1930 MHz频率占用度显著提升,1200~2000 MHz频率占用度提升至6.78%。对比《500米口径球面射电望远镜(FAST)干扰保护要求》,信号谱功率通量密度未全部达到要求的阈值以下。上述观测与FAST调试运行同步进行,所测信号包括了FAST调试过程中测控、通信等信号,上述分析研究对改进FAST周边电磁环境和指导FAST运行具有重要的参考意义。

Calculating real-time surface deformation for large active surface radio antennas using a graph neural network

This paper presents an innovative surrogate modeling method using a graph neural network to compensate for gravitational and thermal deformation in large radio telescopes.Traditionally,rapid compensation is feasible for gravitational deformation but not for temperature-induced deformation.The introduction of this method facilitates real-time calculation of deformation caused both by gravity and temperature.Constructing the surrogate model involves two key steps.First,the gravitational and thermal loads are encoded,which facilitates more efficient learning for the neural network.This is followed by employing a graph neural network as an end-to-end model.This model effectively maps external loads to deformation while preserving the spatial correlations between nodes.Simulation results affirm that the proposed method can successfully estimate the surface deformation of the main reflector in real-time and can deliver results that are practically indistinguishable from those obtained using finite element analysis.We also compare the proposed surrogate model method with the out-of-focus holography method and yield similar results.

Targeted Search for Fast Radio Bursts with Nanshan 26m Radio Telescope

Fast radio bursts(FRBs)are radio transients that are bright and have short duration,with their physical mechanism not being fully understood.We conducted a targeted search for bursts from FRB 20201124A between 2021 June 2and July 20.High time-resolution data were collected for 104.5 hr using the ROACH2-based digital backend.We introduce the details of our FRB search pipeline which is based on HEIMDALL and FETCH.Testing of the injected mock FRBs search could help us better understand the performance of the pipelines,and improve the search algorithms and classifiers.To study the efficiency of our pipeline,5000 mock FRBs were injected into the data and searched using the pipeline.The results of the mock FRB search show that our pipeline can recover almost all(?90%)the injected mock FRBs above a signal-to-noise ratio(S/N)threshold of 15,and the performance is still acceptable(?80%)for injected S/Ns from 10 to 15.The recovery fraction displays relations with S/N,dispersion measure and pulse width.No bursts were detected from FRB 20201124A in the middle of 2021.The non-detection of FRB 20201124A may be due to its quiet phase window or no emission above the threshold of the Nanshan telescope.

The Science of Radio Astronomy: An Investigation of Crab Nebula

The science of radio astronomy focuses on the observation and study of celestial objects by reading their radio waves. The 5 meter radio-telescope is able to observe different radio sources using a C-band LNB. This research was essentially focused on Crab Nebula, also known as Taurus A. The study led to interesting observations, which were validated numerically using various scientific computing software. The radio waves emitted by Taurus A are readable by the RTL-SDR, a software defined radio receiver. This device is capable of reading radio frequencies in the range of 0.5 MHZ to 1700 MHZ.

ITU-R P.2001模型在FAST宁静区的适用性研究

为验证、研究ITU-R P.2001模型在FAST宁静区的适用性,首先系统分析了该模型所考虑的传播机理,给出了预测流程;其次,在FAST宁静区选择了多个公众移动基站,在周边开展外场测试并采集测试数据;最后,对比分析了实地测量值与模型预测值,结果表明预测结果与实测结果之间呈现较为相符的总体趋势,两者间的均方根误差为7.93 dB。上述研究结果可为FAST宁静区无线电设备电磁兼容分析、ITU-R P.2001预测模型区域化本地化研究及应用提供理论参考。

基于空间位形的FAST索网有限元模型修正方法研究

500m口径射电望远镜FAST采用柔性索网作为主要支承结构,在使用过程中频繁张拉索网主索,不可避免的造成主索的预应力损失,使主索的实际受力状态与有限元模型中的计算索力出现偏差,从而影响主索疲劳寿命的评估结果。考虑索网结构的内力分布与空间位形相关,本文根据现场监测数据提出一种基于空间位形的索网结构有限元模型修正方法,首先获取索力数据和节点的坐标数据,然后根据节点的平衡方程和约束条件建立非线性规划数学模型,最后利用序列二次规划算法(SQP)求解实现结构有限元模型的修正。数值模拟结果显示,索力误差在10%范围内的索数目占比由修正前的56.8%提升到87.7%,修正后有限元模型与实际受力状况更为接近,验证了该方法的可行性。本文所提出的方法不仅可以用于修正FAST索网结构的有限元模型,同时也可为其他类似的大型索网结构模型修正提供参考。

VLBI observations with the Kunming 40-meter radio telescope

The Kunming 40-meter radio telescope is situated in the yard of the Yunnan Astronomical Observatory （Longitude： 102.8° East, Latitude： 25.0° North） and saw its first light in 2006 May. The Kunming station successfully joined the VLBI tracking of China＇s first lunar probe ＂Chang＇E-1＂ together with the other Chinese telescopes： the Beijing Miyun 50-meter radio telescope, Urumqi Nanshan 25-meter radio telescope, and Shanghai Sheshan 25-meter radio telescope, and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications. Due to its location, the Kunming station can significantly improve the u - v coverage of the European VLBI Network （EVN）, in particular, in long baseline observations. We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station. The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 17. From scheduling the observations to performing the post correlations, the Kunming station shows its good compatibility to work with the EVN. The imaging result of the extended source 1156＋295 further demonstrates that the Kunming station greatly enhances the EVN performance.

Preface:Planning the scientific applications of the Five-hundred-meter Aperture Spherical radio Telescope

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is by far the largest telescope of any kind ever built. FAST produced its first light in September 2016 and it is now under commissioning, with normal operation to commence in late 2019. During testing and early science operation, FAST has started making astronomical discoveries, particularly pulsars of various kinds, including millisecond pulsars, binaries, gamma-ray pulsars, etc. The papers in this mini-volume propose ambitious observational projects to advance our knowledge of astronomy, astrophysics and fundamental physics in many ways.Although it may take FAST many years to achieve all the goals explained in these papers, taken together they define a powerful strategic vision for the next decade.

Active sub-reflector research for a large radio telescope

This paper proposes an active sub-reflector suitable for large radio telescopes,which can compensate both of the deformation of the main reflector and sub-reflector position offsets.The mathematical formula of the main reflector deformation compensated by the sub-reflector is deduced based on Cassegrain and Gregory antenna structures.The position of the sub-reflector is adjustable to compensate for defocusing errors on high and low elevations,which are mainly caused by the deformation of the sub-reflector supporting legs.In this paper,the method of obtaining the optimum position of the sub-reflector from the aperture phase by the interferometric method is introduced.The actual measurement is verified on the Tianma 65 m radio telescope,which provides a new way to diagnose the position error of the sub-reflector.

Pulsar timing observations with Haoping Radio Telescope

We report pulsar timing observations carried out in L-band with NTSC’s 40-meter Haoping Radio Telescope(HRT),which was constructed in 2014.These observations were carried out using the pulsar machine we developed.Timing observations toward millisecond pulsar J0437–4715 obtain a timing residual(r.m.s.)of 397 ns in the time span of 284 days.Our observations successfully detected Crab pulsar’s glitch that happened on 2019 July 23.

A quark nova in the wake of a core-collapse supernova:a unifying model for long duration gamma-ray bursts and fast radio bursts

By appealing to a quark nova(QN;the explosive transition of a neutron star to a quark star) in the wake of a core-collapse supernova(CCSN) explosion of a massive star,we develop a unified model for long duration gamma-ray bursts(LGRBs) and fast radio bursts(FRBs).The time delay(years to decades)between the SN and the QN,and the fragmented nature(i.e.,millions of chunks) of the relativistic QN ejecta are key to yielding a robust LGRB engine.In our model,an LGRB light curve exhibits the interaction of the fragmented QN ejecta with turbulent(i.e.,filamentary and magnetically saturated) SN ejecta which is shaped by its interaction with an underlying pulsar wind nebula(PWN).The afterglow is due to the interaction of the QN chunks,exiting the SN ejecta,with the surrounding medium.Our model can fit BAT/XRT prompt and afterglow light curves simultaneously with their spectra,thus yielding the observed properties of LGRBs(e.g.,the Band function and the X-ray flares).We find that the peak luminositypeak photon energy relationship(i.e.,the Yonetoku law),and the isotropic energy-peak photon energy relationship(i.e.,the Amati law) are not fundamental but phenomenological.FRB-like emission in our model results from coherent synchrotron emission(CSE) when the QN chunks interact with non-turbulent weakly magnetized PWN-SN ejecta,where conditions are prone to the Weibel instability.Magnetic field amplification induced by the Weibel instability in the shocked chunk frame sets the bunching length for electrons and pairs to radiate coherently.The resulting emission frequency,luminosity and duration in our model are consistent with FRB data.We find a natural unification of high-energy burst phenomena from FRBs(i.e.,those connected to CCSNe) to LGRBs including X-ray flashes(XRFs) and X-ray rich GRBs(XRR-GRBs) as well as superluminous SNe(SLSNe).We find a possible connection between ultra-high energy cosmic rays and FRBs and propose that a QN following a binary neutron star merger can yield a short duration GRB(SGRB) with fits to BAT/XRT light curves.