Sensitive Radio Telescope Research Articles

Prospects for cosmological research with the FAST array: 21-cm intensity mapping survey observation strategies

Precise cosmological measurements are essential for understanding the evolution of the universe and the nature of dark energy. The Five-hundred-meter Aperture Spherical Telescope (FAST), the most sensitive single-dish radio telescope, has the potential to provide the precise cosmological measurements through neutral hydrogen 21 cm intensity mapping sky survey. This paper primarily explores the potential of technological upgrades for FAST in cosmology. The most crucial upgrade begins with equipping FAST with a wide-band receiver (0 < z < 2.5). This upgrade can enable FAST to achieve higher precision in cosmological parameter estimation than the Square Kilometre Array Phase 1 Mid-Frequency Array. On this basis, expanding to a FAST array (FASTA) consisting of six identical FASTs would offer significant improvements in precision compared to FAST. Additionally, compared with the current results from the data combination of cosmic microwave background, baryon acoustic oscillations (optical galaxy surveys), and type Ia supernovae, FASTA can provide comparable constraints. Specifically, for the dark-energy equation-of-state parameters, FASTA can achieve σ(w 0) = 0.09 and σ(wa ) = 0.33.

Study of Five-Hundred-Meter Aperture Spherical Telescope Feed Cabin Time-Series Prediction Studies Based on Long Short-Term Memory-Self-Attention.

The Five-hundred-meter Aperture Spherical Telescope (FAST), as the world's most sensitive single-dish radio telescope, necessitates highly accurate positioning of its feed cabin to utilize its full observational potential. Traditional positioning methods that rely on GNSS and IMU, integrated with TS devices, but the GNSS and TS devices are vulnerable to other signal and environmental disruptions, which can significantly diminish position accuracy and even cause observation to stop. To address these challenges, this study introduces a novel time-series prediction model that integrates Long Short-Term Memory (LSTM) networks with a Self-Attention mechanism. This model can hold the precision of feed cabin positioning when the measure devices fail. Experimental results show that our LSTM-Self-Attention model achieves a Mean Absolute Error (MAE) of less than 10 mm and a Root Mean Square Error (RMSE) of approximately 12 mm, with the errors across different axes following a near-normal distribution. This performance meets the FAST measurement precision requirement of 15 mm, a standard derived from engineering practices where measurement accuracy is set at one-third of the control accuracy, which is around 48 mm (according to the accuracy form the official threshold analysis on the focus cabin of FAST). This result not only compensates for the shortcomings of traditional methods in consistently solving feed cabin positioning, but also demonstrates the model's ability to handle complex time-series data under specific conditions, such as sensor failures, thus providing a reliable tool for the stable operation of highly sensitive astronomical observations.

Enhanced monochromatic photon emission from millicharged co-interacting dark matter

We study a millicharged co-interacting dark matter scenario, where the primary dark matter constituent is the dark photon A′ and the secondary component is the fermion χ. In this model, χ interacts with A′ via a U(1)′ interaction while being millicharged with respect to normal photons. Our investigation focuses on the oscillation of A′ dark matter into photons within the background of χ particles, revealing that the A′ − χ scattering rate benefits from a Bose enhancement of the A′ final state. As the oscillation production rate is directly linked to the scattering rate, the conversion of A′ dark matter into monochromatic photons experiences significant amplification owing to this Bose enhancement, especially when the scattering rate Γsca approaches the dark photon mass mA′. These converted monochromatic photons are detectable through radio telescopes and can induce distortions in the Cosmic Microwave Background (CMB) spectrum. We find that the sensitivity of radio telescopes and the constraints imposed by CMB distortion on the kinetic mixing parameter are notably heightened compared to scenarios without the subdominant millicharged dark matter.

Host Galaxies for Four Nearby CHIME/FRB Sources and the Local Universe FRB Host Galaxy Population

We present the host galaxies of four apparently nonrepeating fast radio bursts (FRBs), FRB 20181223C, FRB 20190418A, FRB 20191220A, and FRB 20190425A, reported in the first Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) catalog. Our selection of these FRBs is based on a planned hypothesis testing framework where we search all CHIME/FRB Catalog-1 events that have low extragalactic dispersion measure (<100 pc cm−3), with high Galactic latitude (∣b∣ > 10°) and saved baseband data. We associate the selected FRBs with galaxies with moderate to high star formation rates located at redshifts between 0.027 and 0.071. We also search for possible multimessenger counterparts, including persistent compact radio and gravitational-wave sources, and find none. Utilizing the four FRB hosts from this study, along with the hosts of 14 published local Universe FRBs (z < 0.1) with robust host association, we conduct an FRB host demographics analysis. We find all 18 local Universe FRB hosts in our sample to be spirals (or late-type galaxies), including the host of FRB 20220509G, which was previously reported to be elliptical. Using this observation, we scrutinize proposed FRB source formation channels and argue that core-collapse supernovae are likely the dominant channel to form FRB sources. Moreover, we infer no significant difference in the host properties of repeating and apparently nonrepeating FRBs in our local Universe FRB host sample. Finally, we find the burst rates of these four apparently nonrepeating FRBs to be consistent with those of the sample of localized repeating FRBs observed by CHIME/FRB. Therefore, we encourage further monitoring of these FRBs with more sensitive radio telescopes.

The Lofar Global Citizenship Radio Array - “Gloray” (Ska-Low-North)

Abstract This talk describes a proposed transformation of LOFAR, the world’s largest, most sensitive high-resolution radio telescope that operates at low frequencies (&lt;300 MHz), into a multidisciplinary intercontinental facility that will be a unique engine for capacity building and development throughout Europe, North Africa, the Middle East and West Asia. As an astronomical array, GLORAY would be the “Hubble Space Telescope” of low-frequency radio astronomy, having a resolution more than 50 times better than any other presently planned low-frequency facility, including SKA-LOW. The mutually interdependent network of LOFAR antenna stations that presently stretch from Ireland to Latvia would be extended to cover North Africa, the Middle East and West Asia and converted into “innovation hubs”. These would form an intercontinental network for pure research, applied research, capacity building, education and science diplomacy within and between the participating countries.

Detection of intended and unintended emissions from Starlink satellites in the SKA-Low frequency range, at the SKA-Low site, with an SKA-Low station analogue

Context. Intended and unintended radio emissions from satellites can interfere with sensitive radio telescopes in the frequency ranges of key experiments in astrophysics and cosmology. We detect strong intended and unintended electromagnetic radiation from Starlink satellites at the site of the future SKA-Low facility in Western Australia, using an SKA-Low prototype station known as the Engineering Development Array version 2 (EDA2). Aims. We aim to show that Starlink satellites are easily detectable utilising a configuration of low frequency radio antennas representative of an SKA-Low ‘station’ and that our results complement similar findings with the LOFAR telescope. Methods. Utilising the EDA2 at frequencies of 137.5 MHz and 159.4 MHz, we detected trains of Starlink satellites on March 17 and 18, 2023, and November 16 and 17, 2021, respectively, via the formation of all-sky images with a frequency resolution of 0.926 MHz and a time resolution of 2 s. Time differencing techniques were utilised to isolate and characterise the transmissions from Starlink and other satellites. Results. We observed Starlink satellites reaching intensities of 106 Jy beam−1, with the detected transmissions exhibiting a range of behaviours, from periodic bursts to steady transmission. The results are notable because they demonstrate that Starlink satellites are detected in the SKA-Low frequency range, transmitting both intentionally and unintentionally. Follow-up work and discussion are needed to identify the cause of this unintentional radiation as it has the potential to interfere with SKA-Low science. It is likely that the transmission levels will need to be reduced by orders of magnitude to bring the impact on radio astronomy to potentially manageable levels. Conclusions. Our results indicate that both intended and unintended radiation from Starlink satellites will be detrimental to key SKA science goals without mitigation. A continued conversation with SpaceX could potentially result in future mitigations which the EDA2 instrument could efficiently monitor and characterise at the SKA-Low site.

Fine Structures of Radio Bursts from Flare Star AD Leo with FAST Observations

Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their substructures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope. We detected many radio bursts in the 2 days of observations with fine structures in the form of numerous millisecond-scale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability, which may be related to stellar flares or interactions with a planetary companion.

Radio emission from the first quasars at z = 6–15

ABSTRACT Nearly 300 quasars have now been found at z &amp;gt; 6, including nine at z &amp;gt; 7. They are thought to form from the collapse of supermassive primordial stars to 104–105 M⊙ black holes at z ∼ 20–25, which then rapidly grow in the low-shear environments of rare, massive haloes fed by strong accretion flows. Sensitive new radio telescopes such as the Next-Generation Very Large Array (ngVLA) and the Square Kilometre Array (SKA) could probe the evolution of these objects at much earlier times. Here, we estimate radio flux from the first quasars at z ∼ 6–15 at 0.5–12.5 GHz. We find that SKA and ngVLA could detect a quasar like ULAS J1120+0641, a 1.35 × 109 M⊙ black hole at z = 7.1, at much earlier stages of evolution, z ∼ 14–16, with 100 h integration times in targeted searches. The advent of these new observatories, together with the JWST, Euclid, and the Roman Space Telescope, will inaugurate the era of z ≲ 15 quasar astronomy in the coming decade.

Pulsar Discovery Prospect of FASTA

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has discovered more than 650 new pulsars, which account for 20% of our known Galactic pulsar population. In this paper, we estimate the prospect of a pulsar survey with a radio telescope array to be planned—the FAST Array (FASTA), consists of six “FAST-type” telescopes. Such a sensitive radio telescope array would be a powerful instrument in probing the pulsar population deep into our Galaxy as well as in nearby galaxies. We simulate the FASTA pulsar discovery prospects with different Galactic pulsar population models and instrumental parameter combinations. We find that FASTA could detect tens of thousands of canonical pulsars and well-over thousands of millisecond pulsars. We also estimate the potential yield if the FASTA is used to search for pulsars from the nearby spiral galaxy M31, and find that it would probably discover around a hundred new radio pulsars.

RFI flagging in solar and space weather low frequency radio observations

ABSTRACTRadio spectroscopy provides a unique inspection perspective for solar and space weather research, which can reveal the plasma and energetic electron information in the solar corona and inner heliosphere. However, radio-frequency interference (RFI) from human activities affects sensitive radio telescopes, and significantly affects the quality of observation. Thus, RFI detection and mitigation for the observations is necessary to obtain high quality science-ready data. The flagging of RFI is particularly challenging for the solar and space weather observations at low frequency, because the solar radio bursts can be brighter than the RFI, and may show similar temporal behaviour. In this work, we investigate RFI flagging methods for solar and space weather observations, including a strategy for aolagger, and a novel method that makes use of a morphology convolution. These algorithms can effectively flag RFI while preserving solar radio bursts.

HINOTORI and Its Perspectives in the Black-Hole Jet Study

Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at centimeter wavelengths. In order to realize high-sensitivity mm-VLBI observations in the East Asia region, we are promoting the HINOTORI (Hybrid Installation project in NObeyama, Triple-band ORIented) project, which aims to launch the wide-band and simultaneous triple-band (22/43/86 GHz) VLBI system with the Nobeyama 45 m Radio Telescope (NRO45). The simultaneous 22/43 GHz observation mode has already been operated for the open-use program. We have recently completed the performance evaluation of the receiver and observing system at 86 GHz. In addition, a new wide-band VLBI back-end system has been installed on the NRO45 and the performance of this receiving system has been found to be sufficient to meet scientific requirements. Currently, we are performing commissioning observations to establish regular VLBI operation with simultaneous triple-band mode together with the Korean VLBI Network. The participation of the NRO45 is expected to strengthen the mm-VLBI observation network in the East Asia region and to be a very powerful addition with respect to the science of of black hole jets.

Observations of decameter carbon radio recombination lines in several galactic directions. Part 1. Experimental study

Subject and Purpose. Since decameter carbon radio recombination lines (RRLs) were detected for the first time more than forty years ago, they have significantly extended our knowledge of the physics, kinematics and chemistry of the cold rarefied interstellar medium (ISM). A large number of these lines have been observed towards various Galactic radio sources. The present paper describes our studies of decameter carbon RRLs in such Galactic directions as the sight-lines to the S140 emission nebula and to the large volume of cold neutral hydrogen known as the GSH 139-03-69 super shell. Methods and Methodology. Observations within a 1-MHz frequency band centered at 26 MHz were performed using the UTR-2 radio telescope and a multi-channel digital correlator. The UTR-2 is still the world largest and the most sensitive low-frequency radio telescope. Results.We report the detection of decameter carbon RRL series C627α – C637α from the medium lying towards the S140 nebula. The extents of RRL forming regions have been estimated. It is suggested that RRLs in the S140 direction are formed in the local ISM lying along the line of sight. The RRL-forming region is probably associated with omnipresent diffuse neutral HI gas in the Galactic plane rather than with S140 nebula itself. Toward the GSH 139-03-69 super shell, decameter RRLs have been detected as well. Likewise, they apparently originate from the local medium lying along the sight-line. Yet, the spectrum contains a RRL component corresponding to the absorption of the cold gas of the GSH 139-03-69 itself in the ISM. Conclusions. The obtained results indicate great possibilities of decameter carbon RRLs not only for cold ISM probing but also for making a good auxiliary tool for studying large complexes of extremely cold hydrogen HI in the Galaxy.

Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive radio telescope for pulsar observations. We make polarimetric measurements of a large number of faint and distant pulsars using the FAST. We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo. Significant improvements are also made for some basic pulsar parameters for 15 of them. We analyse the newly determined rotation measures (RMs) for the Galactic magnetic fields by using these 134 halo pulsars, together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot (GPPS) survey or previously known pulsars without RMs. The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2~$\mu$G for the large-scale toroidal halo magnetic fields. The scale height of the halo magnetic fields is found to be at least 2.7$\pm$0.3~kpc. The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of $26^{\circ}<l<90^{\circ}$ gives evidence for the clockwise magnetic fields (viewed from the north Galactic pole) in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm, and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.

The discovery of an unusual repeating radio transient

We have discovered a new kind of repeating radio source using a sensitive low-frequency radio telescope in outback Western Australia. Its unusual properties indicate it could be a kind of never-before-detected object: an ultra-long-period magnetar.

Searching for pulsars associated with polarised point sources using LOFAR: Initial discoveries from the TULIPP project

Discovering radio pulsars, particularly millisecond pulsars (MSPs), is important for a range of astrophysical applications, such as testing theories of gravity or probing the magneto-ionic interstellar medium. We aim to discover pulsars that may have been missed in previous pulsar searches by leveraging known pulsar observables (primarily polarisation) in the sensitive, low-frequency radio images from the Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS), and have commenced the Targeted search, using LoTSS images, for polarised pulsars (TULIPP) survey. For this survey, we identified linearly and circularly polarised point sources with flux densities brighter than 2 mJy in LoTSS images at a centre frequency of 144 MHz with a 48 MHz bandwidth. Over 40 known pulsars, half of which are MSPs, were detected as polarised sources in the LoTSS images and excluded from the survey. We have obtained beam-formed LOFAR observations of 30 candidates, which were searched for pulsations using coherent de-dispersion. Here, we present the results of the first year of the TULIPP survey. We discovered two pulsars, PSRs J1049+5822 and J1602+3901, with rotational periods ofP = 0.73 s and 3.7 ms, respectively. We also detected a further five known pulsars (two slowly-rotating pulsars and three MSPs) for which accurate sky positions were not available to allow a unique cross-match with LoTSS sources. This targeted survey presents a relatively efficient method by which pulsars, particularly MSPs, may be discovered using the flexible observing modes of sensitive radio telescopes such as the Square Kilometre Array and its pathfinders/precursors, particularly since wide-area all-sky surveys using coherent de-dispersion are currently computationally infeasible.

Radio Frequency Interference Mitigation and Statistics in the Spectral Observations of FAST

In radio astronomy, radio frequency interference (RFI) becomes more and more serious for radio observational facilities. The RFI always influences the search and study of the interesting astronomical objects. Mitigating the RFI becomes an essential procedure in any survey data processing. The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is an extremely sensitive radio telescope. It is necessary to find out an effective and precise RFI mitigation method for FAST data processing. In this work, we introduce a method to mitigate the RFI in FAST spectral observation and make a statistic for the RFI using ∼300 h FAST data. The details are as follows. First, according to the characteristics of FAST spectra, we propose to use the Asymmetrically Reweighted Penalized Least Squares algorithm for baseline fitting. Our test results show that it has a good performance. Second, we flag the RFI with four strategies, which are to flag extremely strong RFI, flag long-lasting RFI, flag polarized RFI, and flag beam-combined RFI, respectively. The test results show that all the RFI above a preset threshold could be flagged. Third, we make a statistic for the probabilities of polarized XX and YY RFI in FAST observations. The statistical results could tell us which frequencies are relatively quiescent. With such statistical data, we are able to avoid using such frequencies in our spectral observations. Finally, based on the ∼300 h FAST data, we obtained an RFI table, which is the most complete database currently for FAST.

Ageing Characterization Under Thermal Test of a Receiver Unit for a Radio Telescope

The Square Kilometer Array low (SKAlow) is an outstanding project aiming at building the world&#x2019;s largest and most sensitive radio telescope. The Australian Murchison Shire desert has been chosen as location for the low-frequency antennas because of many reasons, such as the atmospheric above the site and the radio quietness due to one of the most remote location worldwide. This location is the optimal choice by a radio astronomy and RF engineering point of views. However, it brings several drawbacks in terms of system availability due to the high temperature conditions that deeply affect the electronics reliability, and the difficulties and the costs associated to maintenance tasks performed in a remote location. Thus, it is fundamental to study the reliability and functional performances of the auxiliary electronic devices in the antennas array using adequate aging tests under temperature stress conditions. The experimental activities carried out in this work allowed to investigate the outbreak of failure mechanisms due to aging and hot temperature conditions in the receiver unit for low-frequency antennas of the SKA project. The experimental results are intended to better determine the strengths and weaknesses of the device under test in order to optimize its installation, its maintenance operations and its functionalities.

Toward a Spanish SKA Regional Centre fully engaged with open science

The Square Kilometre Array Observatory (SKAO) will build the most sensitive radio telescopes on Earth. To address fundamental questions in astrophysics, fundamental physics, and astrobiology, it will require processing and handling complex and extremely massive data close to the exascale, hence constituting a technological challenge for the next decade. Approximately 600 Peta-bytes (PB) of calibrated data will be delivered to the network of SKA Regional Centers (SRCs) worldwide. As a world-leading scientific instrument, SKAO aims to pursue the best practices in scientific methodology. Remarkably, it includes the reproducibility of its data as a metric of success. We present the Spanish prototype of an SRC (SPSRC), which supports preparatory scientific activities for the future SKA projects. These include science with SKA precursors and pathfinders while promoting Open Science practices as a way to enable scientific reproducibility. We describe the key developments and components of the SPSRC that align with these objectives. In particular, we describe the performed work on hardware and cloud computing infrastructure, science archive, software and services, user support and training, and collaboration with other SRCs. The resulting SPSRC platform is flexible enough to host heterogeneous projects while being scalable toward the demanding SKA requirements.

MOSS I: Double radio relics in the Saraswati supercluster

ABSTRACT Superclusters are the largest objects in the Universe, and they provide a unique opportunity to study how galaxy clusters are born at the junction of the cosmic web as well as the distribution of magnetic fields and relativistic particles beyond cluster volume. The field of radio astronomy is going through an exciting and important era of the Square Kilometer Array (SKA). We now have the most sensitive functional radio telescopes, such as the MeerKAT, which offers high angular resolution and sensitivity towards diffuse and faint radio sources. To study the radio environments around supercluster, we observed the (core part of) Saraswati supercluster with the MeerKAT. From our MeerKAT Observation of the Saraswati Supercluster (MOSS) project, the initial results of the pilot observations of two massive galaxy clusters, A2631 and ZwCl2341.1+0000, which are located around the dense central part of the Saraswati supercluster, were discussed. In this paper, we describe the observations and data analysis details, including direction-dependent calibration. In particular, we focus on the ZwCl2341.1+0000 galaxy cluster, which hosts double radio relics and puzzling diffuse radio source in the filamentary network. We have imaged these double radio relics in our high resolution and sensitive L-band MeerKAT observation and a puzzling radio source, located between relics, in the low-resolution image. We also derived the spectra of double radio relics using MeerKAT and archival GMRT observations. The following papers will focus on the formation of radio relics and halo, as well as radio galaxy properties in a supercluster core environment.

Towards the prediction of molecular parameters from astronomical emission lines using Neural Networks

Molecular astronomy is a field that is blooming in the era of large observatories such as the Atacama Large Millimeter/Submillimeter Array (ALMA). With modern, sensitive, and high spectral resolution radio telescopes like ALMA and the Square Kilometer Array, the size of the data cubes is rapidly escalating, generating a need for powerful automatic analysis tools. This work introduces MolPred, a pilot study to perform predictions of molecular parameters such as excitation temperature (Tex) and column density (log(N)) from input spectra by the use of neural networks. We used as test cases the spectra of CO, HCO+, SiO and CH3CN between 80 and 400 GHz. Training spectra were generated with MADCUBA, a state-of-the-art spectral analysis tool. Our algorithm was designed to allow the generation of predictions for multiple molecules in parallel. Using neural networks, we can predict the column density and excitation temperature of these molecules with a mean absolute error of 8.5% for CO, 4.1% for HCO+, 1.5% for SiO and 1.6% for CH3CN. The prediction accuracy depends on the noise level, line saturation, and number of transitions. We performed predictions upon real ALMA data. The values predicted by our neural network for this real data differ by 13% from the MADCUBA values on average. Current limitations of our tool include not considering linewidth, source size, multiple velocity components, and line blending.