Radio Empire Morse, Daniel Ryan
2020, 2020-11-10
eBook
Initially created to counteract broadcasts from Nazi Germany, the BBC's Eastern Service became a cauldron of global modernism and an unlikely nexus of artistic exchange. Daniel Ryan Morse ...demonstrates the significance of the Eastern Service for global Anglophone literature and literary broadcasting.
Abstract We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their ...characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts ( z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M ⊙ ) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1−8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm.
The Beautiful Mess in Abell 2255 Botteon, A.; Brunetti, G.; van Weeren, R. J. ...
Astrophysical journal/The Astrophysical journal,
07/2020, Letnik:
897, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby (z = 0.0806) merging galaxy cluster hosting one of the first radio halos ever ...detected in the intracluster medium (ICM). The deep LOFAR images at 144 MHz of the central ∼10 Mpc2 region show a plethora of emission on different scales, from tens of kiloparsecs to above megaparsec sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and nonthermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by the turbulence generating the extended radio halo.
In Tracking the Audience: The Ratings Industry From Analog to Digital, author Karen Buzzard examines the key economic, political, and competitive factors that have influenced ratings methods dominant ...in each of the markets for radio, TV, and the Internet, tracing the practice¹s history from its early beginnings up to its most recent advances. Beginning with the birth of the industry in 1929, Tracking the Audience traces the establishment of a standardized ratings &dquotecurrency&dquote as it evolved to meet the needs of the analog broadcast system, and explores the search for new gold standards necessitated by the devastating effects of the digital revolution. Buzzard examines key challenges to the established system by discussing the movement from traditional sampling methods to new, more transparent measurements. More than a history of the ratings industry itself, it also tracks the evolving business model for the broadcast industry.
Tracking the Audience: The Ratings Industry From Analog to Digital shows how the development of conceptual tools designed to measure and package radio, TV, and Internet audiences is the result of a variety of historical factors. With a detailed examination of ratings providers, their methods, and their attempts to adjust to meet new demands a digital age, this volume explains how a standardized broadcast system of audience measurement ratings has evolved, and where it is going in the future.
When a Russian émigré jazz musician makes his DJ debut on the BBC's airwaves in 1977 with Stevie Wonder's "Sir Duke," no one expects that he, Seva Novgorodsev, would become more popular than just a ...presenter of forbidden Western music--he would liberate the people of the USSR.
The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterizing the physical and evolutionary ...properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper, we present new 150-MHz observations carried out with the LOw-Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6 x 14.7 arcsec and reaches an rms of 160 mu Jy beam super( -1) at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of ... The median spectral index becomes slightly flatter (increasing from ... with decreasing flux density down to S sub( 150) ~10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample, we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 ultra-steep-spectrum sources and 13 peaked-spectrum sources. We estimate that up to 21 per cent of these could have z > 4 and are candidate high-z radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We report on the results of multiwavelength follow-up observations with Gemini, Very Large Array (VLA), and Australia Telescope Compact Array to search for a host galaxy and any persistent ...radio emission associated with FRB 180309. This FRB is among the most luminous FRB detections to date, with a luminosity of >8.7 × 10
32
erg Hz
−1
at the dispersion-based redshift upper limit of 0.32. We used the high-significance detection of FRB 180309 with the Parkes Telescope and a beam model of the Parkes Multibeam Receiver to improve the localization of the FRB to a region spanning approximately
∼
2
′
×
2
′
. We aimed to seek bright galaxies within this region to determine the strongest candidates as the originator of this highly luminous FRB. We identified optical sources within the localization region above our
r
-band magnitude limit of 24.27, 14 of which have photometric redshifts whose fitted mean is consistent with the redshift upper limit (
z
< 0.32) of our FRB. Two of these galaxies are coincident with marginally detected “persistent” radio sources of flux density 24.3
μ
Jy beam
−1
and 22.1
μ
Jy beam
−1
, respectively. Our redshift-dependent limit on the luminosity of any associated persistent radio source is comparable to the luminosity limits for other localized FRBs. We analyze several properties of the candidate hosts we identified, including chance association probability, redshift, and presence of radio emission; however, it remains possible that any of these galaxies could be the host of this FRB. Follow-up spectroscopy on these objects to explore their H
α
emission and ionization contents, as well as to obtain more precisely measured redshifts, may be able to isolate a single host for this luminous FRB.
Abstract
Solar radio emissions provide several unique diagnostics to estimate different physical parameters of the solar corona, which are otherwise simply inaccessible. However, imaging the highly ...dynamic solar coronal emissions spanning a large range of angular scales at radio wavelengths is extremely challenging. At gigahertz frequencies, MeerKAT radio telescope is possibly globally the best-suited instrument at present for providing high-fidelity spectroscopic snapshot solar images. Here, we present the first published spectroscopic images of the Sun made using the observations with MeerKAT in the 880–1670 MHz band. This work demonstrates the high fidelity of spectroscopic snapshot MeerKAT solar images through a comparison with simulated radio images at MeerKAT frequencies. The observed images show extremely good morphological similarities with the simulated images. Our analysis shows that below ∼900 MHz MeerKAT images can recover essentially the entire flux density from the large angular-scale solar disk. Not surprisingly, at higher frequencies, the missing flux density can be as large as ∼50%. However, it can potentially be estimated and corrected for. We believe once solar observation with MeerKAT is commissioned, it will enable a host of novel studies, open the door to a large unexplored phase space with significant discovery potential, and also pave the way for solar science with the upcoming Square Kilometre Array-Mid telescope, of which MeerKAT is a precursor.
Abstract
Solar radio bursts are strongly affected by radio-wave scattering on density inhomogeneities, changing their observed time characteristics, sizes, and positions. The same turbulence causes ...angular broadening and scintillation of galactic and extragalactic compact radio sources observed through the solar atmosphere. Using large-scale simulations of radio-wave transport, the characteristics of anisotropic density turbulence from 0.1
R
⊙
to 1 au are explored. For the first time, a profile of heliospheric density fluctuations is deduced that accounts for the properties of extrasolar radio sources, solar radio bursts, and in situ density fluctuation measurements in the solar wind at 1 au. The radial profile of the spectrum-weighted mean wavenumber of density fluctuations (a quantity proportional to the scattering rate of radio waves) is found to have a broad maximum at around (4–7)
R
⊙
, where the slow solar wind becomes supersonic. The level of density fluctuations at the inner scale (which is consistent with the proton resonance scale) decreases with heliocentric distance as
〈
δ
n
i
2
〉
(
r
)
≃
2
×
10
7
r
/
R
⊙
−
1
−
3.7
cm
−6
. Due to scattering, the apparent positions of solar burst sources observed at frequencies between 0.1 and 300 MHz are computed to be essentially cospatial and to have comparable sizes, for both fundamental and harmonic emission. Anisotropic scattering is found to account for the shortest solar radio burst decay times observed, and the required wavenumber anisotropy is
q
∥
/
q
⊥
= 0.25–0.4, depending on whether fundamental or harmonic emission is involved. The deduced radio-wave scattering rate paves the way to quantify intrinsic solar radio burst characteristics.
In the Age of Enlightenment the German philosopher Immanuel Kant encouraged people to use their own mind as the basis for reasoning instead of following dogmatic religious rules - Sapere aude! (dare ...to know!) - Today wireless communication networks are increasingly becoming aware of the conditions of its their component parts and surrounding environment. Cognition, a continuous process involving sensing, reasoning, understanding and reacting, can be applied to wireless networks in order to adapt the system to the highly dynamic wireless ecosystem. The ultimate goals are to enhance the efficiency in the use of radio resources as well as to improve both link and network performance. This book presents a detailed overview of a rapidly emerging topic in modern communications: cognitive wireless networks. The key aspects of cognitive and cooperative principles in wireless networks are discussed in this book. Furthermore, Cognitive Wireless Networks advocates the concept of breaking up the cellular communication architecture by introducing cooperative strategies among wireless devices. Cognitive wireless networking is the key to success in handling the upcoming dynamic network configurations and exploiting this cross-over to the fullest extent. As wireless networks become pervasive, highly populated and increasingly complex, the essential preconditions for exploiting rich interactions among mobile devices are better fulfilled. Today, these trends are giving rise to new communications paradigms making use of cooperation and cognition as the main underlying principles. Cognition, together with its complementary principle cooperation, confer to the wireless networks some degree of consciousness or understanding about their own existence, such as internal structure, capabilities, relationships to the outside world, limitations, current use of radio resources and many more. Current wireless networks are aware of their surrounding environment to a very limited extent, but in future wireless networks this capability will be highly developed, as a consequence of exploiting jointly cooperative and cognitive principles. Especially for cooperative wireless networks, where the communication scenario is highly dynamic, the mobile devices need to adapt their capabilities in a flexible manner, taking advantage of cognitive principles.
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