Aperture Spherical Radio Telescope Research Articles

The Two Emission States of PSR B1534+12

Abstract We have observed PSR B1534+12 (J1537+1155), a pulsar with a neutron star companion, using the Five-hundred-meter Aperture Spherical radio Telescope. We found that this pulsar shows two distinct emission states: a weak state with a wide pulse profile and a burst state with a narrow pulse profile. The weak state is always present. We cannot, with our current data, determine whether the pulse energy of the weak state follows a normal or a log-normal distribution. The burst state energy distribution follows a power law. The amplitude of the single-pulse emission in the burst state varies significantly; the peak flux intensity of the brightest pulse is 334 times stronger than that of the average pulse. We also examined the timing precision achievable using only bright pulses, which showed no demonstrable improvement because of pulse jitter and therefore quantified the jitter noise level for this pulsar.

Recognition of FAST reflector nodes based on Canny operator

The reflector system of Five-hundred-meter Aperture Spherical radio Telescope (FAST) is designed as 4450 rigid panels supported by a flexible cable-net structure. We use 10 total stations to measure 2225 nodes of the cable-net and then control the shape of the reflectors. Every time, it takes at least 35 minutes to finish the calibration of the whole cable-net once. It is indeed far too inefficient. Thus, we developed a set of highly efficient instrument CRRS (CCD Rotation Ranging System). It is based on photogrammetry and can finish the measurement in 1 minute. However, the target we used in CRRS is active target, and it has serious electromagnetic interference problems to affect the use of FAST. Take the above reasons into consideration, we plan to identify the nodes by taking the gap between the reflector panels as the feature condition. The new method can take the place of active targets to finish the measuring task. The present work focuses on the following aspects. First, combined with the characteristics of FAST reflector images, the representative algorithms of image edge detection are discussed. Second, the process of node extraction is introduced in detail so that we know that it works. In addition, experimental results are given to draw a conclusion so that Canny algorithm was used for continuous research of reflector edge detection.

Pulsar Candidate Sifting Using Multi-input Convolution Neural Networks

Abstract Pulsar candidate sifting is an essential process for discovering new pulsars. It aims to search for the most promising pulsar candidates from an all-sky survey, such as the High Time Resolution Universe (HTRU), Green Bank Northern Celestial Cap (GBNCC), Five-hundred-meter Aperture Spherical Radio Telescope, etc. Recently, machine learning (ML) has become a hot topic in investigations of pulsar candidate sifting. However, one typical challenge in ML for pulsar candidate sifting comes from the learning difficulty arising from the high class imbalance between the observed numbers of pulsars and non-pulsars. Therefore, this work proposes a novel framework for candidate sifting, named Multi-input Convolutional Neural Networks (MICNN). MICNN is an architecture of deep learning with four diagnostic plots of a pulsar candidate as its inputs. To train our MICNN on a highly class-imbalanced data set, a novel image augmentation technique is proposed, as well as a three-stage training strategy. Experiments on observations from HTRU and GBNCC show the effectiveness and robustness of these proposed techniques. In the experiments on HTRU, our MICNN model achieves a recall rate of 0.962 and a precision rate of 0.967 even in a highly class-imbalanced test data set.

The atomic gas of star-forming galaxies atz∼ 0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope

Context.We report new H Iobservations of fourz ∼ 0.05 VALES galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST).Aims.FAST is the largest single-dish telescope in the world, with a 500 m aperture and a 19-Beam receiver. Exploiting the unprecedented sensitivity provided by FAST, we aim to study the atomic gas content, via the H I21 cm emission line, in low-zstar formation galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES). Together with previous Atacama Large Millimeter/submillimeter Array (ALMA) CO(J = 1−0) observations, the H Idata provides crucial information to measure the gas mass and dynamics.Methods.As a pilot H Igalaxy survey, we targeted four local star-forming galaxies atz ∼ 0.05. In particular, one of them has already been detected in H Iby the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing a careful comparison. We use an ON-OFF observing approach that allowed us to reach an rms of 0.7 mJy beam−1at a 1.7 km s−1velocity resolution within only 20 min ON-target integration time.Results.In this Letter, we demonstrate the extraordinary capability of the FAST 19-beam receiver to push the detectability of the H Iemission line of extra-galactic sources. The H Iemission line detected by FAST shows good consistency with the previous Arecibo telescope ALFALFA results. Our observations are put into context with previous multi-wavelength data to reveal the physical properties of these low-zgalaxies. We find that the CO(J = 1−0) and H Iemission line profiles are similar. The dynamical mass estimated from the H Idata is an order of magnitude higher than the baryon mass and the dynamical mass derived from the CO observations, implying that the mass probed by dynamics of H Iis dominated by the dark matter halo. In one case, a target shows an excess of CO(J = 1−0) in the line centre, which can be explained by an enhanced CO(J = 1−0) emission induced by a nuclear starburst showing high-velocity dispersion.

The conceptual designs of radio telescopes in Guizhou karst region

The Five-hundred-meter Aperture Spherical Radio Telescope (FAST)—a large-aperture radio telescope constructed in a karst depression—is completing its commissioning. Several studies have been performed using FAST, including the discovery of over 100 pulsars. Nevertheless, the ability of a single telescope is still limited. The construction of other radio telescopes and telescope arrays around FAST will promote its use for new types of observations and help to achieve additional scientific goals. Based on the analyses of the basic properties of the karst depressions in the Guizhou Province—e.g., their morphologies, aperture diameters, and depths—some conceptual designs have been proposed for large-scale radio telescopes and telescopic arrays. They include a drift-scan survey array, a quasi-steerable radio telescope, a tilted radio telescope, and a fixed-reflector, low-frequency spherical radio telescope. The sky coverage and sensitivity have been calculated for each design, and possible science goals have been discussed, including searches for pulsars and fast radio bursts, as well as studies of variable radio sources. By coordinating their observations with FAST, these telescopes will greatly expand the observational capabilities of FAST and yield substantially more science results, especially in the area of time-domain astronomy.

An in-depth investigation of 11 pulsars discovered by FAST

ABSTRACT We present timing solutions and analyses of 11 pulsars discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These pulsars were discovered using an ultrawide bandwidth receiver in drift-scan observations made during the commissioning phase of FAST, and were then confirmed and timed using the 64-m Parkes Radio Telescope. Each pulsar has been observed over a span of at least one year. Highlighted discoveries include PSR J0344−0901, which displays mode-changing behaviour and may belong to the class of so-called swooshing pulsars (alongside PSRs B0919+06 and B1859+07); PSR J0803−0942, whose emission is almost completely linearly polarized; and PSRs J1900−0134 and J1945+1211, whose well-defined polarization angle curves place stringent constraints on their emission geometry. We further discuss the detectability of these pulsars by earlier surveys, and highlight lessons learned from our work in carrying out confirmation and monitoring observations of pulsars discovered by a highly sensitive telescope, many of which may be applicable to next-generation pulsar surveys. This paper marks one of the first major releases of FAST-discovered pulsars, and paves the way for future discoveries anticipated from the Commensal Radio Astronomy FAST Survey.

Research on key technologies for installation and maintenance of reflector of FAST

The reflector of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) consists of 4450 reflector units. Installation of the reflector faces the challenges of large span, complex terrain, serious interference, complex processes, high position and inability to use conventional equipment. The installation technology for the flexible reflector with a large span was specially studied and designed. Two half-span arc-moving cable cranes and two transfer trucks were jointly operated along a path that follows a circular beam. After installation of the reflector was completed, two half-span cable cranes were merged into a set of full-span cable cranes for maintenance of the reflector. Installation of the reflector combines features of unit and site topography of FAST. The installation technology follows scientific and reasonable practices, and is highly efficient and convenient. It represents a breakthrough in many key technologies in construction and maintenance techniques. It has promoted related technical progress in the construction and maintenance of complex projects. It has also provided an important reference for the construction and maintenance of similar projects, and has strong significance and applicability.

A motion planning algorithm for the feed support system of FAST

The paper relates to a motion planning algorithm for the feed support system of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). To enhance the stability of the feed support system, the start/termination planning segments are adopted with an acceleration and deceleration section. The source switching planning adopts a combination of a line segment and focal segment to realize stable control of the feed support system. Besides, during the observation trajectory, a transition segment which is not used for observation data is planned with a required time. Through an example simulation, a smooth change is realized via the motion planning algorithm and presented in this paper.

Prognostics and health management of FAST cable-net structure based on digital twin technology

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) will be fully commissioned later in 2019. Once commissioned, operation and maintenance of FAST will be the most prominent task. The unique working mode of active shape-changing of FAST cable-net structure makes the traditional maintenance way, which combines routine inspection with preventive maintenances not only expensive, but also unable to effectively avoid potential risks in operations. Therefore, it is necessary to develop an economical and reliable operation/maintenance technology for FAST cable-net structure. In this paper, a Prognostics and Health Management (PHM) system is proposed based on the advanced Digital Twin (DT) technology. Through the finite element analysis of DT model, the current safety status of FAST cable-net is evaluated, and the fatigue life of components in the cable-net is predicted. Hence Condition-Based Maintenance (CBM) of FAST cable-net structure can be realized. The PHM system described in this paper can effectively guarantee the healthy and safe operation of the FAST cable-net structure, greatly improve the maintenance efficiency and reduce the cost for maintenance works.

Development of wideband orthomode transducers for FAST cryogenic receiver system

This paper describes the design, construction, and performance of the wideband orthomode transducers (OMTs) for the L- (1.2–1.8 GHz), the S- (2–3 GHz) and the P- (0.56–1.12 GHz) band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These OMTs operate at the cryogenic temperature of 70K to reduce their thermal noise contribution to the receiver chains. The development on the FAST L- and S-band quad-ridged waveguide (QRWG) OMTs is carried out based on the theoretical mode analysis. In view of the miniaturization of FAST cryogenic receiver system at P-band, a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength. The proposed L-, S- and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator (HFSS), and then manufactured, tested at room temperature. Measurement of FAST cryogenic receiver system noise is also performed with the L-, S- and P-band OMTs installed. The measured results fully comply with the design specifications.

RFI measurements and mitigation for FAST

Radio Frequency Interference (RFI) mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope (FAST) due to its high sensitivity. In order to protect FAST from RFI, an Electromagnetic Compatibility (EMC) study has been carried out and the operation of a Radio Quiet Zone (RQZ) is ongoing. RFI measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI sources. Based on the measurement results and theoretical analysis, various EMC methods have been implemented for the telescope to decrease the RFIs. Meanwhile, the main RFI sources in the FAST RQZ, such as mobile stations, broadcast stations and navigation instruments, have been identified, and the technical measures have been adopted to protect the quiet radio environment around the site. The early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods.

Opportunities to search for extraterrestrial intelligence with the FAST

The discovery of ubiquitous habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, has ushered in a renaissance in the search for extraterrestrial intelligence (SETI). Large scale SETI activities are now underway at numerous international facilities. The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-aperture radio telescope in the world, and is well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence. SETI is one of the five key science goals specified in the original FAST project plan. A collaboration with the Breakthrough Listen Initiative was initiated in 2016 with a joint statement signed both by Dr. Jun Yan, the then director of National Astronomical Observatories, Chinese Academy of Sciences (NAOC), and Dr. Peter Worden, Chairman of the Breakthrough Prize Foundation. In this paper, we highlight some of the unique features of FAST that will allow for novel SETI observations. We identify and describe three different signal types indicative of a technological source, namely, narrow band, wide-band artificially dispersed and modulated signals. Here, we propose observations with FAST to achieve sensitivities never before explored. For nearby exoplanets, such as TESS targets, FAST will be sensitive to an EIRP of 1.9 × 1011 W, well within the reach of current human technology. For the Andromeda Galaxy, FAST will be able to detect any Kardashev type II or more advanced civilization there.

FAST VLBI: current status and future plans

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-dish radio telescope in the world, and is now being commissioned after the first light in September 2016. Very long baseline interferometry (VLBI) is among the key science topics according to the original design. The FAST VLBI system has been established, and the first VLBI fringe has been successfully obtained. FAST will significantly improve the sensitivity of the existing VLBI networks in the future, and some science projects in need of high sensitivity will benefit from its participation.

An open-loop control algorithm of the active reflector system of FAST

An open-loop control algorithm is put forward for continuous paraboloid deformation of the active reflector system of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The method is based on a calibration database and interpolation in 2D spatial domain and temperature domain, respectively. It is completely independent of real-time measurement of cable nodes so that it has advantage of working all-weather and no additional electro-magnetic interference (EMI). Furthermore, its control accuracy can be effectively improved via reasonable layout of the calibrated paraboloids and increasing calibration accuracy. Meanwhile deformation safety is considered via calibration as well. Finally its control accuracy is also confirmed via site measurements of paraboloid deformations.

The time and frequency standard system for FAST receivers

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope (FAST), including the system design, stability measurements and pulsar timing observations. The stability and drift rate of the frequency standard are calculated using 1-year monitoring data. The UTC-NIM Disciplined Oscillator (NIMDO) system improves the system time accuracy and stability to the level of 5 ns. Pulsar timing observations were carried out for several months. The weighted RMS of timing residuals reaches the level of less than 3.0 μs.

Preface: Key technologies for enhancing the performance of FAST

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) passed its national acceptance inspection on 2020 January 11. This special issue includes a total of 15 papers, which are selected to introduce the status of FAST’s performance and demonstrate the key technologies applied to FAST. The presented performance parameters can provide an important reference for scientists to propose observations with FAST. The key technologies presented in these papers include design and implementation in the measurement and control system, electromagnetic compatibility system, and receiver system. Finally, scientific achievements obtained by FAST during the commissioning phase are also reported.

The design of China Reconfigurable ANalog-digital backEnd for FAST

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) was launched on 2016 September 25. From early 2017, we began to use the FAST wideband receiver, which was designed, constructed and installed on the FAST in Guizhou, China. The front end of the receiver is composed an uncooled Quad Ridge Flared Horn feed (QRFH) with the frequency range of 270 to 1620 MHz, and a cryostat operating at 10 K. We have cooperated with the Institute of Automation of the Chinese Academy of Sciences to develop the China Reconfigurable ANalog-digital backEnd (CRANE). The system covers the 3 GHz operating band of FAST. The hardware part of the backend includes an Analog Front-end Board, a wideband high precision Analog Digital Converter, and a FAST Digital Back-end. Analog circuit boards, field programmable gate arrays, and control computers form a set of hardware, software, and firmware platforms to achieve flexible bandwidth requirements through parameter changes. It is also suitable for the versatility of different astronomical observations, and can meet specific requirements. This paper briefly introduces the hardware and software of CRANE, as well as some observations of the system.

Pilot Hi survey of Planck Galactic Cold Clumps with FAST

We present a pilot Hi survey of 17 Planck Galactic Cold Clumps (PGCCs) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Hi Narrow Self-Absorption (HINSA) is an effective method to detect cold Hi being mixed with molecular hydrogen H2 and improves our understanding of the atomic to molecular transition in the interstellar medium. HINSA was found in 58% PGCCs that we observed. The column density of HINSA was found to have an intermediate correlation with that of 13CO, following (N(HINSA)) = (0.52 ± 0.26) (N13CO) + (10 ± 4.1). Hi abundance relative to total hydrogen [Hi]/[H] has an average value of 4.4 × 10–3, which is about 2.8 times of the average value of previous HINSA surveys toward molecular clouds. For clouds with total column density NH > 5 × 1020 cm–2, an inverse correlation between HINSA abundance and total hydrogen column density is found, confirming the depletion of cold Hi gas during molecular gas formation in more massive clouds. Non-thermal line width of 13CO is about 0-0.5 km s−1 larger than that of HINSA. One possible explanation of narrower non-thermal width of HINSA is that HINSA region is smaller than that of 13CO. Based on an analytic model of H2 formation and H2 dissociation by cosmic ray, we found the cloud ages to be within 106.7 – 107.0 yr for five sources.

FAST interstellar scintillation observation of PSR B1929+10 and PSR B1842+14

In this paper, we present the Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations of PSRs B1929+10 and B1842+14. Through analysis of the pulsars’ scintillation pattern, we detected the known scintillation arc from PSR B1929+10 and two previously undetected scintillation arcs from B1842+14. We find that the B1929+10 arc’s curvature scales with observing frequency as η− ∝ ν−2.1±0.1 and η+ ∝ ν−1.8±0.2, consistent with Arecibo results and the theoretical expectations of η ∝ ν−2. From the arc curvature, we infer the scattering screen to be located at 0.20±0.02 kpc from the Earth, close to what was measured by RadioAstron at 324 MHz. From B1842+14, we find two scintillation arcs for the first time. The arcs’ curvatures imply that they are caused by two scattering screens located at a distance of 0.3±0.2 kpc and 1.6±0.6 kpc from the Earth, respectively. The screen distance uncertainties mainly come from the uncertainty in pulsar’s dispersion measure (DM)-derived distance. We present these FAST scintillation observations and discuss the future prospect of FAST pulsar scintillation study.

The fundamental performance of FAST with 19-beam receiver at L band

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy, aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9″, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ∼0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral Hi observations toward NGC 672 and polarization observations toward 3C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.