Drift-pair bursts are an unusual type of solar low-frequency radio emission, which appear in the dynamic spectra as two parallel drifting bright stripes separated in time. Recent imaging spectroscopy ...observations allowed for the quantitative characterization of the drifting pairs in terms of source size, position, and evolution. Here, the drift-pair parameters are qualitatively analyzed and compared with the newly developed Monte Carlo ray-tracing technique simulating radio-wave propagation in the inhomogeneous anisotropic turbulent solar corona. The results suggest that drift-pair bursts can be formed due to a combination of refraction and scattering processes, with the trailing component being the result of turbulent reflection (turbulent radio echo). The formation of drift-pair bursts requires an anisotropic scattering with the level of plasma density fluctuations comparable to that in type III bursts, but with a stronger anisotropy at the inner turbulence scale. The anisotropic radio-wave scattering model can quantitatively reproduce the key properties of drift-pair bursts: the apparent source size and its increase with time at a given frequency, the parallel motion of the source centroid positions, and the delay between the burst components. The trailing component is found to be virtually cospatial and following the main component. The simulations suggest that drift-pair bursts are likely to be observed closer to the disk center and below 100 MHz due to the effects of free-free absorption and scattering. The exciter of drift pairs is consistent with propagating packets of whistlers, allowing for a fascinating way to diagnose the plasma turbulence and the radio emission mechanism.
Fast radio bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Nonrepeating FRB observations have had insufficient ...positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single-pulse FRB 180924 to a position 4 kiloparsecs from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from those of the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.
This book presents the fundamentals of wireless communications and services, explaining in detail what RF spectrum management is, why it is important, which are the authorities regulating the use of ...spectrum, and how is it managed and enforced at the international, regional and national levels. The book offers insights to the engineering, regulatory, economic, legal, management policy-making aspects involved. Real-world case studies are presented to depict the various approaches in different countries, and valuable lessons are drawn. The topics are addressed by engineers, advocates and economists employed by national and international spectrum regulators. The book is a tool that will allow the international regional and national regulators to better manage the RF spectrum, and will help operators and suppliers of wireless communications to better understand their regulators.
Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered ...four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x-or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.
Abstract
This paper studied the faint, diffuse extended X-ray emission associated with the radio lobes and the hot gas in the intracluster medium (ICM) environment for a sample of radio galaxies. We ...used shallow (∼10 ks) archival Chandra observations for 60 radio galaxies (7 FR I and 53 FR II) with 0.0222 ≤
z
≤ 1.785 selected from the 298 extragalactic radio sources identified in the 3CR catalog. We used Bayesian statistics to look for any asymmetry in the extended X-ray emission between regions that contain the radio lobes and regions that contain the hot gas in the ICM. In the Chandra broad band (0.5–7.0 keV), which has the highest detected X-ray flux and the highest signal-to-noise ratio, we found that the nonthermal X-ray emission from the radio lobes dominates the thermal X-ray emission from the environment for ∼77% of the sources in our sample. We also found that the relative amount of on-jet axis nonthermal emission from the radio lobes tends to increase with redshift compared to the off-jet axis thermal emission from the environment. This suggests that the dominant X-ray mechanism for the nonthermal X-ray emission in the radio lobes is due to the inverse Compton upscattering of cosmic microwave background (CMB) seed photons by relativistic electrons in the radio lobes, a process for which the observed flux is roughly redshift independent due to the increasing CMB energy density with increasing redshift.
Es innegable la fortaleza de la radio como medio de comunicación en sus recién cumplidos cien años. Incluso el resurgimiento de la ficción a través del podcast y los nuevos medios, deudores del gran ...teatro de las ondas, augura a la radio como medio de expresión un futuro inmediato creativamente revelador. Recordemos que la imaginación es la fuente de la creatividad, y la radio ha sido siempre uno de sus portaestandartes más genuinos.
The emergence of Radio Marca in the Spanish radio landscape, at the beginning of the 21st century, was an event. It was the first radio station in the country to specialize in sports. The company ...history of this outlet is linked to the initiatives of the Recoletos group.
Radio Marca started out in a context in which communications media in Spain were adapting to the new reality brought about by digital technology. It was conceived for digital radio transmission (or DAB, by its Spanish acronym). However, this system was hardly used in Spain, so the project was steered towards an FM system.
This article presents the results of thirteen in-depth interviews with the leaders, professionals, and managers who kicked off the project. It also uses bibliographic sources, including the document with which the Recoletos group applied for the DAB broadcast license.
Our study concludes that Recoletos sports director Manuel Saucedo was key to the horizontal growth of the group. Radio Marca was a gamble from Recoletos, which sought to expand its influence in the sports news market. For that, a pioneering project was begun in Spain, with the aim of creating a radio station specialized in sports news.
O início das transmissões da Radio Marca foi um marco na história da rádio espanhola porque foi a primeira estação de rádio especializada em esportes na Espanha a transmitir sua programação em todo o país 24 horas por dia. A história empresarial da Rádio Marca está ligada à iniciativa do Grupo Recoletos.
A Rádio Marca iniciou suas transmissões em um contexto específico no qual todos os meios de comunicação na Espanha estavam se adaptando à implementação da tecnologia digital no campo do jornalismo. O projeto foi concebido para ser desenvolvido em conjunto com o DAB, um sistema de difusão de sinais que não tem tido sucesso na Espanha. Por conseguinte, a empresa dirigiu o projeto em direção ao sistema FM.
Este documento apresenta os resultados de uma base de estudos de pesquisa com treze entrevistas em profundidade com executivos, gerentes e profissionais que lançaram o projeto. Além disso, foram consultadas fontes bibliográficas, incluindo o documento com o qual o grupo Recoletos solicitou a licença de transmissão no sistema DAB.
O estudo conclui que a figura de Manuel Saucedo foi a chave para o crescimento horizontal do grupo. A Rádio Marca foi a proposta da Recoletos para alargar a sua influência jornalística no mercado da informação desportiva. Para tal, criou um projecto pioneiro em Espanha com a ideia de uma estação de rádio especializada em notícias desportivas como seu conteúdo principal.
La implantación de Radio Marca en el panorama radiofónico español a comienzos del siglo XXI supuso un hito por ser la primera radio especializada de temática deportiva en España. La historia empresarial de este medio está vinculada a la iniciativa del grupo Recoletos.
Radio Marca comenzó sus emisiones en un contexto en el que los medios de comunicación en España se estaban adaptando a la nueva realidad propiciada por la llegada de la tecnología digital. Pese a ser concebido como un proyecto enfocado a la difusión de la señal a través de la llamada radio digital (DAB), la escasa implantación de este sistema obligó a los responsables de la emisora a redirigir la emisión hacia la frecuencia modulada.
Este artículo presenta los resultados de una investigación desarrollada a partir de la realización de trece entrevistas en profundidad a directivos, responsables y profesionales que pusieron en marcha el proyecto, además de la consulta de fuentes bibliográficas, entre las que destaca el documento con el que el grupo Recoletos solicitó la licencia de emisión de DAB.
El estudio concluye que la figura de Manuel Saucedo fue clave para el crecimiento horizontal del grupo. Radio Marca fue una apuesta de Recoletos para extender su influencia periodística en el mercado de la información deportiva. Para ello, creó un proyecto pionero en España con la ideación de una emisora de radio especializada en la actualidad del deporte como contenido principal.
Abstract
Recent developments in astronomical radio telescopes opened new opportunities in imaging and spectroscopy of solar radio bursts at subsecond timescales. Imaging in narrow frequency bands has ...revealed temporal variations in the positions and source sizes that do not fit into the standard picture of type III solar radio bursts, and require a better understanding of radio-wave transport. In this paper, we utilize 3D Monte Carlo ray-tracing simulations that account for the anisotropic density turbulence in the inhomogeneous solar corona to quantitatively explain the image dynamics at the fundamental (near plasma frequency) and harmonic (double) plasma emissions observed at ∼32 MHz. Comparing the simulations with observations, we find that anisotropic scattering from an instantaneous emission point source can account for the observed time profiles, centroid locations, and source sizes of the fundamental component of type III radio bursts (generated where
f
pe
≈ 32 MHz). The best agreement with observations is achieved when the ratio of the perpendicular to the parallel component of the wavevector of anisotropic density turbulence is around 0.25. Harmonic emission sources observed at the same frequency (∼32 MHz, but generated where
f
pe
≈ 16 MHz) have apparent sizes comparable to those produced by the fundamental emission, but demonstrate a much slower temporal evolution. The simulations of radio-wave propagation make it possible to quantitatively explain the variations of apparent source sizes and positions at subsecond timescales both for the fundamental and harmonic emissions, and can be used as a diagnostic tool for the plasma turbulence in the upper corona.
As the Second World War raged throughout Europe, modernist writers often became crucial voices in the propaganda efforts of both sides. Modernism at the Microphone: Radio, Propaganda, and Literary ...Aesthetics During World War II is a comprehensive study of the role modernist writers' radio works played in the propaganda war and the relationship between modernist literary aesthetics and propaganda. Drawing on new archival research, the book covers the broadcast work of such key figures as George Orwell, Orson Welles, Dorothy L. Sayers, Louis MacNeice, Mulk Raj Anand, T.S. Eliot, and P.G. Wodehouse. In addition to the work of Anglo-American modernists, Melissa Dinsman also explores the radio work of exiled German writers, such as Thomas Mann, as well as Ezra Pound's notorious pro-fascist broadcasts. In this way, the book reveals modernism's engagement with new technologies that opened up transnational boundaries under the pressures of war.
Abstract
We present high-resolution, high-sensitivity upgraded Giant Metrewave Radio Telescope observations of the Coma cluster (A1656) at 250–500 MHz and 550–850 MHz. At 250–500 MHz, 135 sources ...have extensions >0.′45 (with peak-to-local-noise ratio >4). Of these, 24 sources are associated with Coma-member galaxies. In addition, we supplement this sample of 24 galaxies with 20 ram pressure stripped (RPS) galaxies from (Chen et al. 2020, eight are included in the original extended radio source sample) and an additional five are detected and extended. We present radio morphologies, radio spectra, spectral index maps, and equipartition properties for these two samples. In general, we find the equipartition properties lie within a narrow range (e.g.,
P
min
= 1–3 × 10
−
13
dynes cm
−2
). Only NGC 4874, one of the two brightest central Coma cluster galaxies, has a central energy density and pressure about five times higher and a radio source age about 50% lower than that of the other Coma galaxies. We find a diffuse tail of radio emission trailing the dominant galaxy of the merging NGC 4839 group that coincides with the
slingshot
tail seen in X-rays. The southwestern radio relic, B1253+275, has a large extent ≈32′ × 10′ (≃1.08 × 0.34 Mpc
2
). For NGC 4789, whose long radio tails merge into the relic and may be a source of its relativistic seed electrons, we find a transverse radio spectral gradient, a steepening from southwest to northeast across the width of the radio source. Finally, radio morphologies of the extended and RPS samples suggest that these galaxies are on their first infall into Coma on (predominantly) radial orbits.
PDF
