Generation Of Radio Telescopes Research Articles

Emulation of the cosmic dawn 21-cm power spectrum and classification of excess radio models using an artificial neural network

ABSTRACT The cosmic 21-cm line of hydrogen is expected to be measured in detail by the next generation of radio telescopes. The enormous data set from future 21-cm surveys will revolutionize our understanding of early cosmic times. We present a machine learning approach based on an artificial neural network that uses emulation in order to uncover the astrophysics in the epoch of reionization and cosmic dawn. Using a seven-parameter astrophysical model that covers a very wide range of possible 21-cm signals, over the redshift range 6 to 30 and wavenumber range 0.05 to $1 \ \rm {Mpc}^{-1}$ we emulate the 21-cm power spectrum with a typical accuracy of $10 - 20~{{\ \rm per\ cent}}$. As a realistic example, we train an emulator using the power spectrum with an optimistic noise model of the square kilometre array (SKA). Fitting to mock SKA data results in a typical measurement accuracy of 2.8 per cent in the optical depth to the cosmic microwave background, 34 per cent in the star-formation efficiency of galactic haloes, and a factor of 9.6 in the X-ray efficiency of galactic haloes. Also, with our modelling we reconstruct the true 21-cm power spectrum from the mock SKA data with a typical accuracy of $15 - 30~{{\ \rm per\ cent}}$. In addition to standard astrophysical models, we consider two exotic possibilities of strong excess radio backgrounds at high redshifts. We use a neural network to identify the type of radio background present in the 21-cm power spectrum, with an accuracy of 87 per cent for mock SKA data.

Commensal transient searches in eight short gamma-ray burst fields

ABSTRACT A new generation of radio telescopes with excellent sensitivity, instantaneous uv coverage, and large fields of view, are providing unprecedented opportunities for performing commensal transient searches. Here, we present such a commensal search in deep observations of short gamma-ray burst fields carried out with the MeerKAT radio telescope in South Africa at 1.3 GHz. These four hour observations of eight different fields span survey lengths of weeks to months. We also carry out transient searches in time slices of the full observations, at time-scales of 15 min and 8 s. We find 122 variable sources on the long time-scales, of which 52 are likely active galactic nuclei, but there are likely also some radio flaring stars. While the variability is intrinsic in at least two cases, most of it is consistent with interstellar scintillation. In this study, we also place constraints on transient rates based on state-of-the-art transient simulations codes. We place an upper limit of 2 × 10−4 transients per day per square degree for transients with peak flux of 5 mJy, and an upper limit of 2.5 × 10−2 transients per day per square degree for transients with a fluence of 10 Jy ms, the minimum detectable fluence of our survey.

Probing quantum gravity with elastic interactions of ultrahigh-energy neutrinos

The next generation of radio telescopes will be sensitive to low-scale quantum gravity by measuring ultrahigh-energy neutrinos. In this work, we demonstrate for the first time that neutrino-nucleon soft interactions induced by TeV-scale gravity would significantly increase the number of events detected by the IceCube-Gen2 radio array in the EeV regime. However, we show that these experiments cannot measure the total cross section using only the angular and energy information of the neutrino flux, unless assumptions on the underlying inelasticity distribution of neutral interactions are made.

面向SKA1时代的科学数据流及阵列模拟分析

After years of planning for the next generation of radio telescopes, the Square Kilometer Array (SKA), construction of SKA phase one (SKA1) started in July 2021. After the formal operation of SKA1, it is expected that 710 petabytes of scientifically processed data will be generated every year. The data will be stored at SKA regional centers around the world for further analysis by scholars. This paper quantitatively analyzes the models of the textcolorblack

IGR J18249−3243: a new GeV-emitting FR II and the emerging population of high-energy radio galaxies

ABSTRACT The advent of new all-sky radio surveys such as the VLA Sky Survey and the Rapid ASKAP Continuum Survey, performed with the latest generation radio telescopes, is opening new possibilities on the classification and study of extragalactic γ-ray sources, specially the underrepresented ones like radio galaxies. In particular, the enhanced sensitivity (sub-mJy level) and resolution (a few arcsec) provides a better morphological and spectral classification. In this work, we present the reclassification of a Fermi/Large Area Telescope (LAT) source as a new Fanaroff–Riley II radio galaxy from the International Gamma-Ray Astrophysics Laboratory sample found to emit at GeV energies. Through a broad-band spectral fitting from radio to γ-ray, we find that the commonly invoked jet contribution is not sufficient to account for the observed γ-ray flux. Our modelling suggests that the observed emission could mainly originate in the lobes (rather than in the radio core) by inverse Compton scattering of radio-emitting electrons off the ambient photon fields. In addition, we cross-correlated the latest generation radio surveys with a list of Fermi/LAT candidate misaligned AGN from the literature, finding four new radio galaxies with a double-lobed morphology. Additional four objects could be classified as such thanks to previous studies in the literature, for a total of nine new radio galaxies with GeV emission presented in this work. We foresee that further objects of this class might be found in the near future with the advent of the Square Kilometer Array, populating the GeV sky.

RadioLensfit: An HPC tool for accurate galaxy shape measurement with SKA

The new generation radio telescopes, such as the Square Kilometre Array (SKA), are expected to reach sufficient sensitivity and resolution to provide large number densities of resolved faint sources, and therefore to open weak gravitational lensing observations to the radio band. In this paper we present RadioLensfit, an open-source tool for an efficient and fast galaxy shape measurement for radio weak lensing shear. It performs a single source model fitting in the Fourier domain, after isolating the source visibilities with a sky model and a faceting technique. This approach makes real sized radio datasets accessible to an analysis in this domain, where data is not yet affected by the systematics introduced by the non-linear imaging process. We detail the implementation of the code and discuss limitations of the source extraction algorithm. We describe the hybrid parallelization MPI+OpenMP of the code, implemented to exploit multi-node HPC infrastructures for accelerating the computation and dealing with very large datasets that possibly cannot entirely be stored in the memory of a single processor. Finally, we present performance results both in terms of measurement accuracy and code scalability on SKA-MID simulated datasets. In particular, we compare shape measurements of 1000 sources at the expected source density in SKA Phase 1 with the ones obtained from the same dataset in a previous work by a joint fitting of the raw visibility data, and show that results are comparable while the computational time is highly reduced.

Square Kilometre Array Low Atomic commercial off-the-shelf correlator and beamformer

The Square Kilometre Array Low is a next generation radio telescope, consisting of 512 antenna stations spread over 65 km, to be built in Western Australia. The correlator and beamformer (CBF) design is central to the telescope signal processing. CBF receives 6 Tera-bits-per-second (Tbps) of station data continuously and processes it in real time with a compute load of 2 Peta-operations-per-second (Pops). The correlator calculates up to 22 million cross products between all pairs of stations, whereas the beamformers (BFs) coherently sum station data to form more than 500 beams. The output of the correlator is up to 7 Tbps, and the BF 2 Tbps. The design philosophy, called “Atomic COTS,” is based on commercial off-the-shelf (COTS) hardware. Data routing is implemented in network switches programmed using the Programming Protocol-Independent Packet Processors (P4) language and the signal processing occurs in COTS field-programmable gate array (FPGA) cards. The P4 language allows routing to be determined from the metadata in the Ethernet packets from the stations. That is, metadata describing the contents of the packet determines the routing. Each FPGA card inputs a fraction of the overall bandwidth for all stations and then implements the processing needed to generate complete science data products. Generation of complete science products in a single FPGA is named here as Atomic processing. A Tango distributed control system configures the multitude of processing modes as well as maintaining the overall health of the CBF system hardware. The resulting 6 Tbps in and 9 Tbps out, 2 Pops Atomic COTS network attached accelerator occupies five racks and consumes 60 kW.

Radio Galaxy Zoo: giant radio galaxy classification using multidomain deep learning

ABSTRACT In this work we explore the potential of multidomain multibranch convolutional neural networks (CNNs) for identifying comparatively rare giant radio galaxies from large volumes of survey data, such as those expected for new generation radio telescopes like the SKA and its precursors. The approach presented here allows models to learn jointly from multiple survey inputs, in this case NVSS and FIRST, as well as incorporating numerical redshift information. We find that the inclusion of multiresolution survey data results in correction of 39 per cent of the misclassifications seen from equivalent single domain networks for the classification problem considered in this work. We also show that the inclusion of redshift information can moderately improve the classification of giant radio galaxies.

Enhanced remote astronomical archive system based on the file-level Unlimited Sliding-Window technique

Data archiving is one of the most critical issues for modern astronomical observations. With the development of a new generation of radio telescopes, the transfer and archiving of massive remote data have become urgent problems to be solved. Herein, we present a practical and robust file-level flow-control approach, called the Unlimited Sliding-Window (USW), by referring to the classic flow-control method in the TCP protocol. Based on the USW and the Next Generation Archive System (NGAS) developed for the Murchison Widefield Array telescope, we further implemented an enhanced archive system (ENGAS) using ZeroMQ middleware. The ENGAS substantially improves the transfer performance and ensures the integrity of transferred files. In the tests, the ENGAS is approximately three to twelve times faster than the NGAS and can fully utilize the bandwidth of network links. Thus, for archiving radio observation data, the ENGAS reduces the communication time, improves the bandwidth utilization, and solves the remote synchronous archiving of data from observatories such as Mingantu spectral radioheliograph. It also provides a better reference for the future construction of the Square Kilometer Array (SKA) Science Regional Center.

Data-Efficient Classification of Radio Galaxies

Abstract The continuum emission from radio galaxies can be generally classified into different morphological classes such as FRI, FRII, Bent, or Compact. In this paper, we explore the task of radio galaxy classification based on morphology using deep learning methods with a focus on using a small scale dataset (∼2000 samples). We apply few-shot learning techniques based on Twin Networks and transfer learning techniques using a pre-trained DenseNet model with advanced techniques like cyclical learning rate and discriminative learning to train the model rapidly. We achieve a classification accuracy of over 92% using our best performing model with the biggest source of confusion being between Bent and FRII type galaxies. Our results show that focusing on a small but curated dataset along with the use of best practices to train the neural network can lead to good results. Automated classification techniques will be crucial for upcoming surveys with next generation radio telescopes which are expected to detect hundreds of thousands of new radio galaxies in the near future.

First results from the REAL-time Transient Acquisition backend (REALTA) at the Irish LOFAR station

Modern radio interferometers such as the LOw Frequency ARray (LOFAR) are capable of producing data at hundreds of gigabits to terabits per second. This high data rate makes the analysis of radio data cumbersome and computationally expensive. While high performance computing facilities exist for large national and international facilities, that may not be the case for instruments operated by a single institution or a small consortium. Data rates for next generation radio telescopes are set to eclipse those currently in operation, hence local processing of data will become all the more important. Here, we introduce the REAL-time Transient Acquisition backend (REALTA), a computing backend at the Irish LOFAR station (I-LOFAR) which facilitates the recording of data in near real-time and post-processing. We also present first searches and scientific results of a number of radio phenomena observed by I-LOFAR and REALTA, including pulsars, fast radio bursts, rotating radio transients, the search for extraterrestrial intelligence, Jupiter, and the Sun.

Using the sample variance of 21 cm maps as a tracer of the ionisation topology

Intensity mapping of the 21 cm signal of neutral hydrogen will yield exciting insights into the Epoch of Reionisation and the nature of the first galaxies. However, the large amount of data that will be generated by the next generation of radio telescopes, such as the Square Kilometre Array, as well as the numerous observational obstacles to overcome, require analysis techniques tuned to extract the reionisation history and morphology. In this context, we introduce a one-point statistic, which we refer to as the local variance,σloc, that describes the distribution of the mean differential 21 cm brightness temperatures measured in two-dimensional maps along the frequency direction of a light cone. The local variance takes advantage of what is usually considered an observational bias, the sample variance. We find the redshift-evolution of the local variance to not only probe the reionisation history of the observed patches of the sky, but also trace the ionisation morphology. This estimator provides a promising tool to constrain the midpoint of reionisation as well as gain insight into the ionising properties of early galaxies.

Multi-epoch searches for relativistic binary pulsars and fast transients in the Galactic Centre

ABSTRACT The high stellar density in the central parsecs around the Galactic Centre makes it a seemingly favourable environment for finding relativistic binary pulsars. These include pulsars orbiting other neutron stars, stellar-mass black holes, or the central supermassive black hole, Sagittarius A*. Here, we present multi-epoch pulsar searches of the Galactic Centre at four observing frequencies, $4.85,\, 8.35,\, 14.6,\, 18.95\, {\rm GHz}$, using the Effelsberg 100-m radio telescope. Observations were conducted 1 yr prior to the discovery of, and during monitoring observations of, the Galactic Centre magnetar PSR J1745−2900. Our data analysis features acceleration searches on progressively shorter time series to maintain sensitivity to relativistic binary pulsars. The multi-epoch observations increase the likelihood of discovering transient or nulling pulsars, or ensure orbital phases are observed at which acceleration search methods work optimally. In ${\sim}147\, {\rm h}$ of separate observations, no previously undiscovered pulsars have been detected. Through calibration observations, we conclude this might be due to insufficient instantaneous sensitivity, caused by the intense continuum emission from the Galactic Centre, its large distance, and, at higher frequencies, the aggregate effect of steep pulsar spectral indices and atmospheric contributions to the system temperature. Additionally, we find that for millisecond pulsars in wide circular orbits $({\lesssim}800\, {\rm d})$ around Sagittarius A*, linear acceleration effects cannot be fully corrected in deep observations $(9\, {\rm h})$ with existing software tools. Pulsar searches of the Galactic Centre with the next generation of radio telescopes – such as MeerKat, ngVLA, and SKA1-mid – will have improved chances of uncovering this elusive population.

Методика побудови первинної матриці похибок радіотелескопа РТ-32 в автоматизованому режимі

2020 was the year of introduction of the Ukrainian new generation radio telescope RT-32 into the experimental operation. The test results of maser hydrogen and hydroxyl lines obtained during the experimental operation confirmed the correctness of the calculations and technological solutions of Ukrainian scientists and manufacturers Consortium. One of the further development directions of RT-32 as a radio astronomical research tool is to increase the accuracy of pointing the radio telescope to radio astronomical sources. One of the further development directions of RT-32 as a radio astronomical research tool is to increase the accuracy of pointing the radio telescope to astronomical radio sources. The latter is to be achieved by automating the processes of guidance error matrices formation and their integration during the observations. The formation of such a matrix presupposes taking into account the structural features of the antenna system and weather condition. The paper presents the results of geodetic measurements of the antenna system surface on different elevation angle, construction of the 3D model of the reflector. The method of constructing the error matrix, which at this stage of research provides the necessary simplicity of perception and interpretation of the obtained results by the human operator, is proposed. The results of the developed method verification using reference radio sources are given and the error matrices of elevation and azimuth pointing (dimension 81x81 elements) obtained with the use of said method are presented. The introduction of the results presented in the article into the radio telescope control system allowed increasing the accuracy of RT-32 radio telescope pointing in the C- and K- bands to the value of ~36″. This work partially was supported by Latvian Council of Science project "Joint Latvian-Ukrainian study of peculiar radio galaxy “Perseus A” in radio and optical bands. Nr: lzp-2020/2-0121".

Design of the cryogenic system of the wideband phased array feed for QTT

Phased array feeds (PAFs), which illuminate the dish with digitally synthesized beams instead of separated horns, provide the capability for wider and continuous field-of-view surveys. As a promising technology for next generation radio telescopes, PAFs will provide the Qi Tai Telescope (QTT), which will be next world-class fully steerable radio telescope, an opportunity of reaching several cutting-edge science goals. This paper presents a brief introduction of the wideband PAF for QTT, and the detailed design and simulation of the cryogenic system. Based on this design, a scaled prototype of the spherical vacuum window, which is the key part of the cryogenic system, has been built and the performance is verified.

Modelling neutron star–black hole binaries: future pulsar surveys and gravitational wave detectors

ABSTRACT Binaries comprised of a neutron star (NS) and a black hole (BH) have so far eluded observations as pulsars and with gravitational waves (GWs). We model the formation and evolution of these NS+BH binaries – including pulsar evolution – using the binary population synthesis code COMPAS. We predict the presence of a total of 50–2000 binaries containing a pulsar and a BH (PSR+BHs) in the Galactic field. We find the population observable by the next generation of radio telescopes, represented by the SKA and MeerKAT, current (LIGO/Virgo) and future (LISA) GW detectors. We conclude that the SKA will observe 1–80 PSR+BHs, with 0–4 binaries containing millisecond pulsars. MeerKAT is expected to observe 0–40 PSR+BH systems. Future radio detections of NS+BHs will constrain uncertain binary evolution processes such as BH natal kicks. We show that systems in which the NS formed first (NSBH) can be distinguished from those where the BH formed first (BHNS) by their pulsar and binary properties. We find 40 per cent of the LIGO/Virgo observed NS+BHs from a Milky Way like field population will have a chirp mass ≥3.0 M⊙. We estimate the spin distributions of NS+BHs with two models for the spins of BHs. The remnants of BHNS mergers will have a spin of ∼0.4, whilst NSBH merger remnants can have a spin of ∼0.6 or ∼0.9 depending on the model for BH spins. We estimate that approximately 25–1400 PSR+BHs will be radio alive whilst emitting GWs in the LISA frequency band, raising the possibility of joint observation by the SKA and LISA.

Метод автоматичної побудови матриці похибок радіотелескопа РТ-32. Методика автоматичного оцінювання похибок наведення

On March 15th, 2021, scientists of the National Space Facilities Control and Tests Center and the Radio Astronomical Institute of the National Academy of Sciences of Ukraine carried out preliminary observations with the Ukrainian new generation radio telescope RT-32 (Zolochiv, Lviv region). The extragalactic radiation of radio galaxy 3C84 (Perseus-A), masers from the galactic molecular cloud W3, radio emission of methanol maser from the galactic radio source G188.946 + 0.886 were observed and successfully recorded. Observations were performed as training in the framework of preparation for the launch of a joint Ukrainian-Latvian radio astronomy project lzp-2020/2-0121. The results of the observations confirmed the world level of RT-32 radio telescope characteristics, the efficiency of the primary error matrix and revealed several shortcomings in the functioning of the tracking system. It was found that the primary tracking error matrix has insufficient discreteness and contains errors of the first and second types. In the article, we present a method of automatic construction of the radio telescope error matrix according to the data of a radiometric receiver and receivers-recorders. The method of construction provides automatic processing of the obtained radiometric data. The results of verification of the developed method using the reference radio sources of different types and the elements of tracking errors’ matrix by the elevation and azimuth obtained when using it are presented. The results obtained with the proposed method were included in the radio telescope control system and allowed us to increase the aiming accuracy of the RT-32 radio telescope.

Recrystallization Behavior of a Pure Cu Connection Interface with Ultrasonic Welding

Three-dimensional metal waveguide components are key components in the next generation of radio telescopes. Ultrasonic additive manufacturing technology combining ultrasonic welding and micro electrical discharge machining (micro-EDM) provides a new method for the overall manufacturing of waveguide elements, and the effective welding of Electrolytic Tough Pitch copper (Cu-ETP) sheets is the key process of this method. This study demonstrates that the orthogonal test optimization method is used to conduct ultrasonic welding tests on Cu-ETP. Specifically, electron backscattered diffraction (EBSD) technology is used to analyze the crystal grains, grain boundary types and texture changes during interface recrystallization. In addition, the finite element software ABAQUS 6.13 is employed to calculate the temperature field in order to determine the possibility of recrystallization of the welding interface. The results showed that the average grain size of the welding interface decreased from 20 to 1~2 μm. The Cu-ETP matrix is mainly composed of coarse grains with high-angle grain boundaries (HAGBs), while a large number of low-angle grain boundaries (LAGBs), subcrystals and fine equiaxed grains appear in the welded joint. At the same time, discontinuous dynamic recrystallization (DDRX) occurs in the less strained area, and continuous dynamic recrystallization (CDRX) is predominant in the greater strain area. The temperature field calculation shows that the peak temperature of the welding interface exceeds the recrystallization temperature of Cu-ETP from 379.05 to 433.2 °C.

Expanding the field of view: station design for the AAMID SKA radio telescope

The new generation radio telescopes, such as the Square Kilometre Array (SKA) currently under construction, will use aperture array, technology for the low frequency regime. For SKA2, the second phase scheduled after the realization of SKA1, aperture array technology is proposed up to 1.4 GHz. The antenna element count, as well as the signal processing cost, of such a system will be high. In this paper we analyze an option to reduce the number of antenna elements by making the array sparse. To reduce the signal processing cost Fast Fourier Transform Beamforming is proposed and it performance is compared to traditional beamforming. To guide the system design a Figure of Merit for the performance cost ratio is proposed and evaluated for various levels of sparsity of the antenna array. It is concluded that, for equal front-end and back-end costs, a sparse system is only marginally better than a dense system. Only when signal processing cost is significantly lower than the front-end hardware, a sparse system can be competitive.

Discovering the most elusive radio relic in the sky: diffuse shock acceleration caught in the act?

ABSTRACT The origin of radio relics is usually explained via diffusive shock acceleration (DSA) or re-acceleration of electrons at/from merger shocks in galaxy clusters. The case of acceleration is challenged by the low predicted efficiency of low Mach number merger shocks, unable to explain the power observed in most radio relics. In this letter, we present the discovery of a new giant radio relic around the galaxy cluster Abell 2249 ($z$ = 0.0838) using Low-Frequency Array (LOFAR). It is special since it has the lowest surface brightness of all known radio relics. We study its radio and X-ray properties combining LOFAR data with uGMRT, JVLA, and XMM. This object has a total power of $L_{1.4\rm\, GHz}=4.1\pm 0.8 \times 10^{23}$ W Hz−1 and integrated spectral index α = 1.15 ± 0.23. We infer for this radio relic a lower bound on the magnetization of $B\ge 0.4\, \mu$G, a shock Mach number of $\mathcal {M}\approx 3.79$, and a low acceleration efficiency consistent with DSA. This result suggests that a missing population of relics may become visible, thanks to the unprecedented sensitivity of the new generation of radio telescopes.