Sources Of Radio Emission Research Articles

Ubiquitous radio emission in quasars: Predominant AGN origin and a connection to jets, dust, and winds

We present a comprehensive study of the physical origin of radio emission in optical quasars at redshifts z < 2.5. We focus particularly on the associations between compact radio emission, dust reddening, and outflows identified in our earlier work. Leveraging the deepest low-frequency radio data available to date (LoTSS Deep DR1), we achieve radio detection fractions of up to 94%, demonstrating the virtual ubiquity of radio emission in quasars, and a continuous distribution in radio loudness. Through our analysis of radio properties, combined with spectral energy distribution modelling of deep multiwavelength photometry, we establish that the primary source of radio emission in quasars is the active galactic nucleus (AGN), rather than star formation. Modelling the dust reddening of the accretion disc emission shows a continuous increase in radio detection in quasars as a function of the reddening parameter E(B − V), suggesting a causal link between radio emission and dust reddening. Confirming previous findings, we observe that the radio excess in red quasars is most pronounced for sources with compact radio morphologies and intermediate radio loudness. We find a significant increase in [O III] and C IV outflow velocities for red quasars not seen in our control sample, with particularly powerful [O III] winds in those around the threshold from radio-quiet to radio-loud. Based on the combined characterisation of radio, reddening, and outflow properties in our sample, we favour a model in which the compact radio emission observed in quasars originates in compact radio jets and their interaction with a dusty, circumnuclear environment. In particular, our results align with the theory that jet-induced winds and shocks resulting from this interaction are the origin of the enhanced radio emission in red quasars. Further investigation of this model is crucial for advancing our understanding of quasar feedback mechanisms and their role in galaxy evolution.

Pulsar Nulling and Vacuum Radio Emission from Axion Clouds.

Nonrelativistic axions can be efficiently produced in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electrodynamics in the pulsar magnetosphere, focusing specifically on the dynamics in the polar caps, where the impact of the axion cloud is expected to be most pronounced. For sufficiently light axions m_{a}≲10^{-7} eV, we show that the axion cloud can occasionally screen the local electric field responsible for particle acceleration and pair production, inducing a periodic nulling of the pulsar's intrinsic radio emission. At larger axion masses, the small-scale fluctuations in the axion field tend to suppress the backreaction of the axion on the electrodynamics; however, we point out that the incoherent oscillations of the axion in short-lived regions of vacuum near the neutron star surface can produce a narrow radio line, which provides a complementary source of radio emission to the plasma-resonant emission processes identified in previous work. While this Letter focuses on the leading order correction to pair production in the magnetosphere, we speculate that there can exist dramatic deviations in the electrodynamics of these systems when the axion backreaction becomes nonlinear.

A Model for Pair Production Limit Cycles in Pulsar Magnetospheres

It was recently proposed that the electric field oscillation as a result of self-consistent e ± pair production may be the source of coherent radio emission from pulsars. Direct particle-in-cell simulations of this process have shown that the screening of the parallel electric field by this pair cascade manifests as a limit cycle, as the parallel electric field is recurrently induced when pairs produced in the cascade escape from the gap region. In this work, we develop a simplified time-dependent kinetic model of e ± pair cascades in pulsar magnetospheres that can reproduce the limit-cycle behavior of pair production and electric field screening. This model includes the effects of a magnetospheric current, the escape of e ±, as well as the dynamic dependence of pair production rate on the plasma density and energy. Using this simple theoretical model, we show that the power spectrum of electric field oscillations averaged over many limit cycles is compatible with the observed pulsar radio spectrum.

Ups and downs in the X-ray emission of the colliding wind binaries HD 168112 and HD 167971

Context. The long-period O-star binary system HD 168112 and the triple O-star system HD 167971 are well-known sources of non-thermal radio emission that arises from a colliding wind interaction. The wind-wind collisions in these systems should result in phase-dependent X-ray emissions. The presence of a population of relativistic electrons in the wind interaction zone could affect the properties of the X-ray emission and make it deviate from the behaviour expected for adiabatic shocks. Aims. We investigate the X-ray emission of these systems with the goals of quantifying the fraction of the X-ray flux arising from wind interactions and determining whether these emissions follow the predictions for adiabatic wind-wind collisions. Methods. Six X-ray observations were collected with XMM-Newton. Three observations were scheduled around the most recent peri-astron passage of HD 168112. Spectra and light curves were analysed and compared with simple predictions of model calculations for X-ray emission from colliding wind systems. Results. The X-ray emission of HD 168112 varies as the inverse of the orbital separation, as expected for an adiabatic wind interaction zone. The relative contribution of intrinsic X-ray emission from wind-embedded shocks varies between 38% at periastron to 81% at apastron. The wind-wind collision zone remains adiabatic even around periastron passage. The X-ray emission of HD 167971 displays variations on the orbital timescale of the inner eclipsing binary. The existing data of this system do not allow us to probe variations on the timescale of the outer orbit. Conclusions. Shock modification due to the action of relativistic electrons does not seem to be efficiently operating in the HD 168112 system. In the existing observations, a significant part of the emission of HD 167971 must arise in the inner eclipsing binary. The origin of this emission is as yet unclear.

Mathematical model of single-channel search for signals of mobile radio communications with one degree of detection in the frequency-time domain.

In the context of a full-scale invasion and military operations for Ukraine's independence, the issues of radio monitoring of radio emission sources of telecommunication networks and systems are gaining special attention and require fundamentally new approaches to the level of informatization, technical implementation and increase of their efficiency. Today, the technical means of radio interception, monitoring and direction finding in the networks of mobile radio communication systems are realized in the form of software and hardware complexes, the most important performance indicators of which are considered to be speed, accuracy of detection and probability of recognition of mobile radio communication means with their information content. At the same time, these issues still remain problematic and require further development of methods and techniques for searching and detecting signals of mobile radio communications in both frequency and time telecommunication channels and their information processing. To solve this issue, the authors propose a mathematical model for searching for mobile radio signals in the frequency-time domain with one degree of detection. The description of the mathematical model for determining the spectral components of signals in the frequency and time domains is carried out using the basic provisions of the theory of directed probability graphs, geometric probabilities with its well-known problem of meeting in a given time interval, and the theoretical foundations of statistical information processing. The analysis of the proposed model shows that the probability of successful completion of the search for a signal with one degree of detection in the frequency-time domain for a given time depends on the value of the signal duration, the number of analyzed frequency channels, the time of signal analysis in each channel, and the probabilities of errors of the first and second kinds The article presents the results of calculations of the value of the probability of successful completion of the signal search as a function of the search time at different values of the analysis time. It is shown that the application of the mathematical model of single-channel search for signals of mobile radio communication means with one degree of detection in the frequency-time domain in practice will make it possible to determine the quality of the radio monitoring process and increase the efficiency of evaluating the spectral components of radio signals in terms of speed, detection accuracy and probability of recognition of mobile radio communication means with further determination of their information content.

Precise Mass, Orbital Motion, and Stellar Properties of the M-dwarf Binary LP 349−25AB

LP 349−25 is a well-studied close stellar binary system comprised of two late M dwarf stars, where both stars are close to the limit between star and brown dwarf. This system was previously identified as a source of gigahertz radio emission. We observed LP 349−25AB over 11 epochs in 2020–2022, detecting both components in this nearby binary system using the Very Long Baseline Array (VLBA). We fit simultaneously the VLBA absolute astrometric positions together with existing relative astrometric observations derived from optical/infrared observations with a set of algorithms that use nonlinear least-squares, genetic algorithm, and Markov Chain Monte Carlo methods to determine the orbital parameters of the two components. We find the masses of the primary and secondary components to be 0.08188 ± 0.00061 M ⊙ and 0.06411 ± 0.00049 M ⊙, respectively, representing one of the most precise mass estimates of any ultracool dwarf (UCD) to date. The primary is a UCD of 85.71 ± 0.64 M Jup, while the secondary has a mass consistent with being a brown dwarf of 67.11 ± 0.51 M Jup. This is one of the very few direct detections of a brown dwarf with VLBA observations. We also find a distance to the binary system of 14.122 ± 0.057 pc. Using stellar evolutionary models, we find the model-derived stellar parameters of both stars. In particular, we obtain a model-derived age of 262 Myr for the system, which indicates that LP 349−25AB is composed of two pre–main-sequence stars. In addition, we find that the secondary star is significantly less evolved than the primary star.

The application of neural networks in the problem of radio monitoring with the use of a two-coordinate radio direction finder and the estimation of their efficiency

Problem statement. Measuring bases of two-coordinate phase direction finders (PDF), as a rule, are located along the same line, while bearing occurs in two planes independently. The procedure for determining the bearing in this case consists in restoring the true wave front and is quite computationally expensive. The study of PDF using a neural network with simultaneous use of information from all possible combinations of measurement bases is of particular interest from the point of view of evaluating the possibility of increasing the probability of correctly eliminating the ambiguity of bearing and increasing the accuracy of bearing, reducing computational costs and reducing the time to determine the bearing. Goal. Evaluation of the effectiveness of the use of artificial neural networks (NN) for direction finding of radio emission sources (RES) in solving radio monitoring problems using two-coordinate PDF, evaluation of the possibility of increasing the probability of correct elimination of ambiguity of bearing and increasing the accuracy of bearing when using all measuring bases of PDF. Results. A model of two-coordinate PDF based on NN has been developed, which makes it possible to evaluate the effectiveness of RES bearing in two planes with variations in model parameters and initial data. The obtained modeling results allow us to conclude that it is possible to create a two-coordinate PDF based on NN. The evaluation of the effectiveness of bearing shows that PDF based on NN has a commensurate accuracy of bearing and a high probability of eliminating ambiguity compared with PDF using classical methods and is somewhat inferior to them at high values of the phase measurement error in the receiving channels. Practical significance. The use of artificial neural networks (NN) for direction finding of radio emission sources (RES) in solving radio monitoring problems and further research on their development will improve the accuracy and reliability of measurements while reducing computational costs.

Using cumulant analysis to recognize digital types of radio signal

Problem statement. Recognition of types of modulation of radio signals is an important task solved in radio engineering systems for various purposes. In radio monitoring tools, information about the type of modulation is used to identify unauthorized sources of radio emission and measure their parameters, in electronic warfare systems - when choosing a more effective type of interference, etc. The article substantiates the relevance of improving methods for recognizing digital types of modulation. It is shown that mixed cumulants of higher orders can be used as modulation features for recognizing types of modulation. Analytical expressions are given for calculating mixed cumulants up to the tenth order inclusive through the values of mixed moments and the value of mixed cumulants for radio signals with the most common types of digital modulation. Recommendations have been developed for the synthesis of algorithms for recognizing the type of modulation based on cumulant analysis. Goal. Obtain mathematical expressions for calculating mixed cumulants up to the tenth order inclusive and determine the values of mixed cumulants to recognize the most common digital types of modulation. Results. A general methodology has been developed for the synthesis of algorithms for recognizing the type of modulation based on cumulant analysis. Practical significance. Application of the developed approach in the design of radio-electronic systems makes it possible to obtain a high probability of correct recognition of digital types of modulation with a relatively low design complexity.

Determination of parameters of radio emission sources

An important task requiring additional research is the analysis of algorithms for determining the carrier frequencies of broadband signals of various durations, allowing for a short pulse duration to reliably determine the parameters of the input signal with positive signal-to-noise ratios. The search for optimal ways to determine the parameters of radio emission sources with minimal input data under operating conditions as part of on-board radio monitoring systems. Methods for determining the frequency and phase characteristics of broadband and narrowband signals with a minimum signal duration (up to 1 microsecond) are presented. A modification of the guiding cosine algorithm has been developed to optimize the resources of the signal processing system. The proposed algorithms make it possible to reduce the amount of computing device resources used. The total computational complexity of the algorithms is relatively low, and the amount of memory used is acceptable for loading into computing nodes from on-board equipment. This work was supported by the Ministry of Science and Higher Education within the State assignment № 075-00701-24-07.

Tracking the motion of a shock along a channel in the low solar corona

Context. Shock waves are excited by coronal mass ejections (CMEs) and large-scale extreme-ultraviolet (EUV) wave fronts and can result in low-frequency radio emission under certain coronal conditions. Aims. In this work, we investigate a moving source of low-frequency radio emission as a CME and an associated EUV wave front move along a channel of a lower density, magnetic field, and Alfvén speed in the solar corona. Methods. Observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, the Nançay Radio Heliograph (NRH), and the Irish Low Frequency Array (I-LOFAR) were analysed. Differential emission measure maps were generated to determine densities and Alfvén maps, and the kinematics of the EUV wave front was tracked using CorPITA. The radio sources’ positions and velocity were calculated from NRH images and I-LOFAR dynamic spectra. Results. The EUV wave expanded radially with a uniform velocity of ∼500 km s−1. However, the radio source was observed to be deflected and appeared to move along a channel of a lower Alfvén speed, abruptly slowing from 1700 km s−1 to 250 km s−1 as it entered a quiet-Sun region. A shock wave with an apparent radial velocity of > 420 km s−1 was determined from the drift rate of the associated Type II radio burst. Conclusions. The apparent motion of the radio source may have resulted from a wave front moving along a coronal wave guide or by different points along the wave front emitting at locations with favourable conditions for shock formation.

Comparison of two options for building three-coordinate electronic intelligence stations

The subject–coordinate measurement methods in ground electronic intelligence (ELINT) stations. The goal is to conduct a comparative analysis of two options for the composition ground ELINT stations in terms of accuracy of measuring coordinate information. The tasks to be solved are as follows: assessing the accuracy of determining the coordinates of the time difference of arrival method (TDOAМ) and hybrid method (HM); obtaining analytical ratios for estimating the root-mean-square error (RMSE) of the accuracy of measuring the altitude of radio emission sources (RES) of these methods; on the basis of the obtained estimates and analytical ratios, a comparative analysis of the methods, under conditions where the accuracy of the coordinate information obtained by both methods is commensurate; and development of recommendations regarding the practical application of HM coordinate measurements. The methods used are: the theory of measurements and the theory of evaluation of coordinate information. The following results were obtained: a comparative analysis of the TDOAМ and HM was performed according to the RMSE of the determination of plane coordinates and the altitude of the RES. The accuracy assessment was performed in a known way, based on the linearization of the functional dependence between the measured primary parameters (range differences, elevation angle) and spatial coordinates by expanding in a Taylor series with the deduction of the first two terms of the series. Calculations have shown that the presence of the third side station has very little effect on the accuracy of determining plane coordinates. Significant differences appear only in the results of estimating the RMSE of the RES altitude. To compare the methods, analytical relationships were obtained for estimating the RMSE of the altitude measurement. The condition is determined under which the accuracy of determining the altitude for the HM is not worse than that for the TDOAМ (the accuracy is the same). Starting from this value and further, when using the HM, the altitude is determined more accurately. Conclusions. An HM of high-precision determination of 3 coordinates in ELINT stations, based on measuring two distance differences and direction finding (DF) in the elevation plane, can, with a smaller number of side stations (two instead of three), provide accuracy no worse than the known TDOAM. However, this requires that the RMSE value for DF in elevation should be tenths of degrees. The practical application of HM is possible for the issuance of target designations on air defense missile systems radar.

Determination of the Direction to the Source of Radio Emission in a Radio Direction Finder with a Five-Element Ring Antenna Array and Total Difference Processing

One of the methods for measuring the direction of arrival of an electromagnetic wave from a radio source by an automatic direction finder with a small antenna base and a limited number of channels of the radio receiving path is proposed. The problems that arise during the implementation of this method are listed, and suggestions for their solution are presented. A block diagram has been obtained and a layout of a radio direction finder has been created, in which the processing device is implemented using a two-channel LimeSDR transceiver. The results of the radio direction finder test for detecting and evaluating the direction of an unmanned aerial vehicle are presented.

СОВМЕСТНЫЙ КВАЗИОПТИМАЛЬНЫЙ АЛГОРИТМ ОБРАБОТКИ РАДИОСИГНАЛОВ ИСТОЧНИКОВ РАДИОИЗЛУЧЕНИЯ АВИАЦИОННЫМ СРЕДСТВОМ РАДИОТЕХНИЧЕСКОГО НАБЛЮДЕНИЯ

The article discusses the development of a joint quasi-optimal algorithm for processing radio signals from radio emission sources by aviation means of radio surveillance. The Bayesian method of a joint quasi-optimal algorithm is used to conduct an independent synthesis of decision rules on discrimination (recognition and detection), resolution, and assessment of the state parameters of a radio source. A block diagram of the developed algorithm is presented. An analysis of the feasibility of a quasi-optimal algorithm is carried out, taking into account the required computational costs for its implementation. Mathematical modeling of the blocks of the developed algorithm was carried out, confirming the increased efficiency of radio signal processing.

Radio sources location determination by the difference-range measuring method based on swarm intelligence

The solution of the location determining problem by the difference-range measuring method in most cases boils down to finding the extremums of functions using various modifications of the gradient optimization method, which has a number of disadvantages, including the need to specify the first approximation of the coordinates of the source, the dependence of the solution of the system of equations on this approximation, as well as the potential possibility of finding a local extremum, instead of a global one. Because of this, there is a need to use global optimization methods that do not have these disadvantages. One of such methods is a heuristic method based on the intelligence of a swarm of particles. The article presents the results of research on the possibility of using swarm intelligence to solve the problem of determining the location of radio sources by the difference-rangefinder method. An analytical description of the method of global optimization of functions based on the intelligence of a "swarm" of particles is presented. The objective function of coordinates of radio emission sources is formed in relation to the difference-rangefinder method of location determination using the Mahalanobis metric. The results of solving the problem of determining the coordinates of radio emission sources based on the search for the minimum of the formed objective function by the "swarm" of particles are presented. The obtained results can be used in the development of mathematical models and software and hardware complexes for determining the location of radio sources by the difference-rangefinder method.

Аналитический метод решения задачи определения местоположения источника радиоизлучения в трёхмерном пространстве

For the location system of time difference of arrival consisting of two arbitrary pairs of receiving stations, an analytical method for solving the problem of estimating the coordinates of a radio emission source in three-dimensional space is proposed, assuming that the height of this source is known or specified.

Main statistical properties of hectometric continuum radiation in near-Earth space

In this work, we have studied the recently discovered hectometric continuum radiation in near-Earth plasma. We have carried out a detailed statistical analysis of the occurrence of a hectometric continuum near Earth at distances 1.1–2 Re, where Re is the Earth radius, for a two-year period, using data from the ERG (Arase) satellite. We have established that the generation of the hectometric radiation depends on the local magnetic time. The continuum radiation of this type is shown to occur mainly at night and in the morning. We have also studied the dependence of the occurrence of hectometric radiation on geomagnetic activity and have demonstrated that there is no direct dependence of the occurrence of hectometric radiation on geomagnetic disturbances. Moreover, the statistical analysis made it possible to localize sources of radio emission of this type in near-Earth space and to show that the source(s) of generation of the hectometric continuum radiation is located at low latitudes.

A search for auroral radio emission from β Pictoris b

Abstract Magnetized exoplanets can serve as the source of auroral radio emissions, allowing us to characterize the magnetospheric properties of these planets. Successful detections of auroral radio emissions from brown dwarfs, as well as from Jupiter, suggest that Jupiter-like planets in distant orbits may also generate radio emissions through a similar mechanism. In this study, we present our search for 250-500 MHz emissions from β Pictoris b, one of the most extensively studied young Jupiter-like planets. We conducted the search using the upgraded Giant Metrewave Radio Telescope (uGMRT). Despite the favourable orbital inclination, no signal was detected, putting 3σ upper limits on the radiation at 0.18 mJy. We translate this limit into constraints on the ionospheric and magnetospheric parameters, assuming that the emission is powered by the Hill current system. While the upper limit is larger by a factor of a few than the nominal estimate of radio intensity, we put constraints on the magnetospheric and ionospheric parameters.

Electromagnetic Accessibility of Starlink User Terminals

The results of assessing the electromagnetic accessibility of radio emission sources of the Starlink satellite communication system are presented. The features of the organizational and technical structure of the system are considered. Its main technical capabilities for organizing the provision of telecommunications services to users of subscriber terminals are analyzed. The technical features of the infrastructure of the Starlink satellite communication system, which are essential for the electromagnetic accessibility of its sources, have been studied. The possibility of radio links for transmitting information content in the upstream and downstream channels of the Starlink satellite communication system was assessed. The main stages of the developed methodology for assessing the electromagnetic accessibility of sources are presented. Analytical expressions are given for calculating the probability of detection and attenuation of signals. The requirements for the sensitivity of the receiving equipment of monitoring equipment are substantiated. Dependences of the level of signal attenuation on the distance of control equipment were obtained.

Основные статистические свойства излучения типа гектометровый континуум в околоземном пространстве

In this work, we have studied the recently discovered hectometric continuum radiation in near-Earth plasma. We have carried out a detailed statistical analysis of the occurrence of a hectometric continuum near Earth at distances 1.1–2 Re, where Re is the Earth radius, for a two-year period, using data from the ERG (Arase) satellite. We have established that the generation of the hectometric radiation depends on the local magnetic time. The continuum radiation of this type is shown to occur mainly at night and in the morning. We have also studied the dependence of the occurrence of hectometric radiation on geomagnetic activity and have demonstrated that there is no direct dependence of the occurrence of hectometric radiation on geomagnetic disturbances. Moreover, the statistical analysis made it possible to localize sources of radio emission of this type in near-Earth space and to show that the source(s) of generation of the hectometric continuum radiation is located at low latitudes.

Four-antenna amplitude direction finder: statistical synthesis and experimental research of signal processing algorithm

The subject of this study is the algorithms for measuring the angular positions of radio emission sources. The goal of this study is to develop an improved algorithm for signal processing in amplitude direction finders that will provide several unambiguous measurement angles at high steepness of the discrimination characteristic by combining measurements of systems with different widths of antenna patterns. The task: to develop an optimal signal processing algorithm for a four-antenna amplitude direction finding system, two antennas of which have a wide radiation pattern and the other two have a narrow one; to test the overall performance of the resulting algorithm by simulating the direction finder; to develop and conduct a study of an experimental model of a four-antenna direction finder, which includes two antennas with wide radiation patterns, two antennas with narrow radiation patterns, radio frequency paths, and a signal processing unit that implements the developed algorithm; to analyze the effectiveness and features of the application of the developed algorithm, and to compare the results of simulation modeling and experimental research. The methods used are statistical methods and optimal solutions for solving problems of statistical synthesis of signal processing algorithms in passive radio systems, computer simulation modeling methods, and experimental research methods. The following results were obtained. The algorithm for signal processing in a four-antenna direction finding system was synthesized using the maximum likelihood method. By simulation modeling, the overall effectiveness of measurement integration in multi-antenna amplitude direction finders was confirmed, and the peculiarities of the synthesized algorithm application were revealed, namely, the need to introduce additional proportionality coefficients into the measurement channels. During the experimental studies of the developed model of the direction finder, the results of the simulation modeling were confirmed. Conclusions. To determine the direction of radiation sources by amplitude direction finders, it is advisable to simultaneously use systems with wide and narrow antenna patterns, the measurements of which are combined by the proposed algorithm. This makes it possible to simultaneously expand the range of unambiguous measurement angles and increase the accuracy of measurements within the equal-signal zone. The disadvantage of using the algorithm is the nonlinear form of the obtained discrimination characteristics and the need to determine additional proportionality coefficients heuristically.