143 research outputs found
The diffuse radio emission around NGC 5580 and NGC 5588
No full textThe galaxy pair NGC 5580 and NGC 5588 is part of a loose group of galaxies. They are surrounded by steep-spectrum, extended radio emission which was previously suggested to be a down-scaled example of Mpc-size radio haloes present in galaxies clusters. We present a multifrequency study of the radio emission aimed to clarify its nature. The source has been observed with the Giant Metrewave Radio Telescope at 235, 325 and 610 MHz and the images obtained were combined with archival data to cover the frequency range 150-1400 MHz. The new observations revealed the presence of a second, fainter lobe on the south-east of NGC 5580. The spectral index study of the source shows a flattening of the spectrum (which implies a younger particle population) close to the two galaxies. We argue that the extended radio emission is the remnant of a past activity cycle of the active galactic nucleus present in NGC 5580 and therefore a notable example of a dying radio galaxy located outside dense environments. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
High-resolution impurity data from the GRIP ice core
No full textThe ice core was drilled during the GRIP project in 1989-1992 at the Summit of the Greenland ice sheet. The length is 3025 m. Present-day accumulation 0.23 m ice/yr. Position 72.57N 37.62W, 3232 m a.s.l.. Impurities were measures as described in Fuhrer et al. (1993). The Holocene data were used for annual-layer identification during the making of the GICC05 and GIC21 time scales, but data are also provided over GS-1 (roughly equivalent to the Younger Dryas) and GI-1 (roughly equivalent to the Bølling-Allerød period). Data from deeper sections exist. Corresponding data author: Hubertus Fischer, Climate and Environmental Physics, Physics Institute, and Oeschger Centre for Climate Change Research, University of Bern, [email protected]
A shock front at the radio relic of Abell 2744
No full textRadio relics are Mpc-scale diffuse radio sources at the peripheries of galaxy clusters which are thought to trace outgoing merger shocks. We present XMM-Newton and Suzaku observations of the galaxy cluster Abell 2744 (z = 0.306), which reveal the presence of a shock front 1.5 Mpc east of the cluster core. The surface-brightness jump coincides with the position of a known radio relic. Although the surface-brightness jump indicates a weak shock with aMach number M = 1.7(-0.3)(+0.5), the plasma in the post-shock region has been heated to a very high temperature (similar to 13 keV) by the passage of the shock wave. The low-acceleration efficiency expected from such a weak shock suggests that mildly relativistic electrons have been re-accelerated by the passage of the shock front.LASTR
A new double radio relic in PSZ1 G096.89+24.17 and a radio relic mass-luminosity relation
No full textRadio relics are diffuse synchrotron sources in galaxy clusters that are believed to trace large-scale shock waves. We have discovered a new double radio relic system in PSZ1 G096.89+24.17 (z = 0.3) and have carried out a full-polarization radio observation using theWesterbork Synthesis Radio Telescope at 1.4 GHz. The observation revealed the presence of two relics located on the two diametrically opposite sides of the cluster and hints of a central radio halo. The linear sizes of the relics are ~0.9 and ~1.4 Mpc. We carried out an analysis of all known double radio relics by using radio, X-ray and Sunyaev-Zel'dovich data. We find that the radio luminosity of double relics is a steep function of the cluster mass, with L<inf>R</inf> a M<sup>2.83±0.39</sup>. If we include single radio relics, this relation is maintained. This dependence has implications for the origin of magnetic fields at the relic's locations
Advanced spectral analysis of ionospheric waves observed with sparse arrays
No full textThis paper presents a case study from a single, 6 h observing period to illustrate the application of techniques developed for interferometric radio telescopes to the spectral analysis of observations of ionospheric fluctuations with sparse arrays. We have adapted the deconvolution methods used for making high dynamic range images of cosmic sources with radio arrays to making comparably high dynamic range maps of spectral power of wavelike ionospheric phenomena. In the example presented here, we have used observations of the total electron content (TEC) gradient derived from Very Large Array (VLA) observations of synchrotron emission from two galaxy clusters at 330 MHz as well as GPS-based TEC measurements from a sparse array of 33 receivers located within New Mexico near the VLA. We show that these techniques provide a significant improvement in signal-to-noise ratio (S/N) of detected wavelike structures by correcting for both measurement inaccuracies and wavefront distortions. This is especially true for the GPS data when combining all available satellite/receiver pairs, which probe a larger physical area and likely have a wider variety of measurement errors than in the single-satellite case. In this instance, we found that the peak S/N of the detected waves was improved by more than an order of magnitude. The data products generated by the deconvolution procedure also allow for a reconstruction of the fluctuations as a two-dimensional waveform/phase screen that can be used to correct for their effects
KNOWN PULSARS IDENTIFIED in the GMRT 150 MHz ALL-SKY SURVEY
No full textWe have used the 150 MHz radio continuum survey (TGSS ADR) from the Giant Metrewave Radio Telescope (GMRT) to search for phase-averaged emission toward all well-localized radio pulsars north of -53° decl. We detect emission toward 200 pulsars with high confidence (=5s) and another 88 pulsars at fainter levels. We show that most of our identifications are likely from pulsars, except for a small number where the measured flux density is confused by an associated supernova or pulsar-wind nebula, or a globular cluster. We investigate the radio properties of the 150 MHz sample and find an unusually high number of gamma-ray binary millisecond pulsars with very steep spectral indices. We also note a discrepancy in the measured flux densities between GMRT and LOFAR pulsar samples, suggesting that the flux density scale for the LOFAR pulsar sample may be in error by approximately a factor of two. We carry out a separate search of 30 well-localized gamma-ray, radio-quiet pulsars in an effort to detect a widening of the radio beam into the line of sight at lower frequencies. No steep-spectrum emission was detected either toward individual pulsars or in a weighted stack of all 30 images
On the effects of the TBM-shield body articulation on tunnelling in soft soil
No full textWhen a Tunnel Boring Machine (TBM) is driven in soft soil, the TBM-shield constantly interacts with the surrounding soil profile excavated by the cutting wheel. The interaction pattern of shield-soil interface displacements determines compression and extension sectors in the surrounding soil. Soil compression is generated when the shield displaces the excavated profile in outward direction; soil extension happens when the shield fits inside that profile. This aspect of TBM behaviour, referred to as shield-soil kinematical interaction, has been demonstrated in a recent study investigating the monitoring data from the Hubertus tunnel in The Hague. The TBM used at the Hubertus tunnel was not equipped with a shield-body articulation. The articulation, designed to limit the undesired shield-soil interactions of the kind described, was present in the TBMs used at the North-South metro line in Amsterdam. This study aims to quantify the consequences of using a shield articulation in terms of shield-soil kinematical interactions. The study, comparing the results from the Hubertus and the North-South line tunnels, revealed remarkable differences, although other discriminating aspects have to be accounted for. The fundamental understanding of the kinematical interactions is crucial to building reliable numerical models for TBM driving in soft soilGeoscience & EngineeringCivil Engineering and Geoscience
EVIDENCE FOR PARTICLE RE-ACCELERATION IN THE RADIO RELIC IN THE GALAXY CLUSTER PLCKG287.0+32.9
No full textRadio relics are diffuse radio sources observed in galaxy clusters, probably produced by shock acceleration during cluster-cluster mergers. Their large size, of the order of 1 Mpc, indicates that the emitting electrons need to be (re)accelerated locally. The usually invoked diffusive shock acceleration models have been challenged by recent observations and theory. We report the discovery of complex radio emission in the Galaxy cluster PLCKG287.0+32.9, which hosts two relics, a radio halo, and several radio filamentary emission. Optical observations suggest that the cluster is elongated, likely along an intergalactic filament, and displays a significant amount of substructure. The peculiar features of this radio relic are that (1) it appears to be connected to the lobes of a radio galaxy and (2) the radio spectrum steepens on either side of the radio relic. We discuss the origins of these features in the context of particle re-acceleration
A powerful double radio relic system discovered in PSZ1 G108.18-11.53: Evidence for a shock with non-uniform Mach number?
No full textDiffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we found M = 2.33-0.26+0.19, while the northern shock Mach number goes fromM= 2.20-0.14+0.07 in the north part down toM= 2.00-0.08+0.03 in the southern region. If the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock
Glucagon-Like Peptide 1 Receptor Agonists in Psychiatry
No full text<p>The glucagon-like peptide 1 (GLP-1)&ndash;based diabetes and obesity drug semaglutide, with trade names Ozempic and Wegovy, will become the second best-selling drug in 2024, with estimated worldwide Ozempic sales of US ~$16 billion. Finally, the pharmacological treatment of obesity seems to have a breakthrough after decades of setbacks, with previous weight-loss medications withdrawn from the market because of serious side effects.</p> <p>In this podcast, the co-author of a guest editorial, <a href="https://doi.org/10.1097/JCP.0000000000001869">&ldquo;Glucagon-Like Peptide 1 Receptor Agonists in Psychiatry,&rdquo;</a> Hubertus Himmerich, MD, reviews the implications of GLP-1 drugs for psychiatry and healthcare globally. The article is published in the May/June 2024 issue of the <em>Journal of Clinical Psychopharmacology.</em> Dr. Himmerich, who is from the department of psychological medicine, Institute of Psychiatry, Psychology &amp; Neuroscience at King's College in London, authored the editorial with Dr. Susan L. McElroy, of the Lindner Center of HOPE, Mason, OH, and the Department of Psychiatry and Behavioral Neuroscience at the University of Cincinnati College of Medicine.</p>
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