Origin of the ring structures in Hercules A Timmerman, R.; van Weeren, R. J.; Callingham, J. R. ...
Astronomy and astrophysics (Berlin),
02/2022, Letnik:
658
Journal Article
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The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring ...structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the
Karl G. Jansky
Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.
We have mapped the powerful radio galaxy Hercules A at six frequencies spanning 1295 to 8440 MHz using the Very Large Array (VLA) in all four configurations. Here we discuss the structure revealed in ...total intensity, spectral index, polarization, and projected magnetic field. Our observations clearly reveal the relation between the bright jets, prominent rings, bulbous outer lobes and faint bridge that make up the radio source. The jets and rings form a coherent structure with a dramatically flatter spectrum than the surrounding lobes and bridge, strongly suggesting that they represent a recently renewed outburst from the active nucleus. The spectrum of the lobes is also steeper than in typical radio sources, and steepens further towards the centre. The compact core is optically thin and also has a remarkably steep spectrum (α≃−1.2). There is some evidence that the old lobe material has been swept up and compressed ahead of the new outburst. We interpret the dramatic asymmetry in the bright structure, and more subtle differences between diffuse lobe structures, in terms of relativistic beaming combined with front-to-back light-travel delays, which mean that we view the two lobes at different stages of the outburst. After correcting for Faraday rotation the projected magnetic field closely follows the edge of the lobes, the jets and the rings; the field pattern in the two lobes is broadly similar. We confirm a strong asymmetry in depolarization and Faraday rotation, with the jet side being the less depolarized and with the flatter spectrum, consistent with general correlations between these asymmetries. The spectral index asymmetry is clearly present in the ‘old’ lobe material and so, at least in this case, is not caused by beaming; but it can be understood in terms of the light-travel delay.
We present the results of the first successful observations of the Pie Town link with the Very Large Array at 74 MHz on Hercules A. The improvement in resolution from 25 to 10 arcsec resolves the ...helical- and ring-like features seen at higher frequencies. We also present new high dynamic range images of this powerful radio galaxy at 325 MHz. Our low-frequency observations confirm the multiple outburst interpretation of the spectral index differences at high frequencies. A comparison between our radio and ROSAT X-ray data does not reveal any association between the X-ray emission from the cluster and the radio lobes. There are no extra regions of radio emission at 74 MHz.
The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring ...structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.
We have made ROSAT Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) X-ray observations to study the intracluster gas surrounding the powerful radio source Hercules A. ...The cluster is luminous in X-rays (Lbol= 4.8 × 1037 W), although apparently poor in optical galaxies, and the host of the radio source is the central dominating galaxy of the cluster. The azimuthally averaged X-ray surface brightness profile is well fitted by a modified King (β) model, with core radius rc= 121 ± 10 kpc and β= 0.74 ± 0.03, but the cluster is elongated parallel to the radio source, especially on the scale of the radio lobes, and fits to individual quadrants give a core radius 50 per cent larger along the radio axis. Part of this elongation appears to be associated with enhanced X-ray emission superimposed on the outer radio lobes, which extend to just over 2rc. There are no obvious depressions in the X-ray emission coincident with the radio lobes, as expected if the relativistic plasma displaces the intracluster medium (ICM). However, we show that these depressions may be quite weak, essentially because the main part of the lobes are outside the cluster core. From the surface brightness profile for the PSPC data the X-ray emission extends out to ∼2.2-Mpc radius. In the absence of the powerful jets (which must be a transient phenomenon on cosmological time-scales), we would expect a cooling flow at the centre of the cluster; but currently it must be substantially disturbed by the expansion of the radio lobes. The PSPC spectrum reveals a cool component of the ICM with 0.5 ≲kT≲ 1 keV in addition to the ≈ 4-keV component detected by ASCA and BeppoSAX. The central cooling time could be as low as 2 Gyr if the cool component is centrally concentrated, otherwise it is around 6 Gyr. Cooling is significant on a Hubble time to a radius of about 90 kpc. The modelled central electron density of n0= 1.0 × 104 m−3 is typical for modest cooling flows. Finally, we have detected faint X-ray emission from a compact central source, with size < 15 kpc and luminosity ≈ 2 × 1036 W.
We report on a simulation study of the calibration potential offered by floating Extensive Air Shower (EAS) detector stations (HELYCON), operating in coincidence with the KM3NeT Mediterranean ...deep-sea neutrino telescope. We describe strategies in order to investigate for possible systematic errors in reconstructing the direction of energetic muons as well as to determine the absolute position of the underwater detector.
We propose the operation of floating Extensive Air Shower (EAS) detector stations in coincidence with the KM3NeT Mediterranean deep-sea neutrino telescope to determine the absolute position and ...orientation of the underwater detector and to investigate possible systematic angular errors. We evaluate the accuracy of the proposed calibration strategies using a detailed simulation of the EAS and KM3NeT detectors.
Letter of intent for KM3NeT 2.0 Adrián-Martínez, S; Aharonian, F; Aiello, S ...
Journal of physics. G, Nuclear and particle physics,
08/2016, Letnik:
43, Številka:
8
Journal Article
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The main objectives of the KM3NeT Collaboration are (i) the discovery and subsequent observation of high-energy neutrino sources in the Universe and (ii) the determination of the mass hierarchy of ...neutrinos. These objectives are strongly motivated by two recent important discoveries, namely: (1) the high-energy astrophysical neutrino signal reported by IceCube and (2) the sizable contribution of electron neutrinos to the third neutrino mass eigenstate as reported by Daya Bay, Reno and others. To meet these objectives, the KM3NeT Collaboration plans to build a new Research Infrastructure consisting of a network of deep-sea neutrino telescopes in the Mediterranean Sea. A phased and distributed implementation is pursued which maximises the access to regional funds, the availability of human resources and the synergistic opportunities for the Earth and sea sciences community. Three suitable deep-sea sites are selected, namely off-shore Toulon (France), Capo Passero (Sicily, Italy) and Pylos (Peloponnese, Greece). The infrastructure will consist of three so-called building blocks. A building block comprises 115 strings, each string comprises 18 optical modules and each optical module comprises 31 photo-multiplier tubes. Each building block thus constitutes a three-dimensional array of photo sensors that can be used to detect the Cherenkov light produced by relativistic particles emerging from neutrino interactions. Two building blocks will be sparsely configured to fully explore the IceCube signal with similar instrumented volume, different methodology, improved resolution and complementary field of view, including the galactic plane. One building block will be densely configured to precisely measure atmospheric neutrino oscillations.
First look at the physics case of TLEP Bicer, M.; Duran Yildiz, H.; Coignet, G. ...
The journal of high energy physics,
01/2014, Letnik:
2014, Številka:
1
Journal Article
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A
bstract
The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the ...absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e
+
e
−
collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the
threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.
The prototype detection unit of the KM3NeT detector Adrián-Martínez, S.; Ageron, M.; Anghinolfi, M. ...
The European physical journal. C, Particles and fields,
02/2016, Letnik:
76, Številka:
2
Journal Article
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A prototype detection unit of the KM3NeT deep-sea neutrino telescope has been installed at 3500m depth 80 km offshore the Italian coast. KM3NeT in its final configuration will contain several ...hundreds of detection units. Each detection unit is a mechanical structure anchored to the sea floor, held vertical by a submerged buoy and supporting optical modules for the detection of Cherenkov light emitted by charged secondary particles emerging from neutrino interactions. This prototype string implements three optical modules with 31 photomultiplier tubes each. These optical modules were developed by the KM3NeT Collaboration to enhance the detection capability of neutrino interactions. The prototype detection unit was operated since its deployment in May 2014 until its decommissioning in July 2015. Reconstruction of the particle trajectories from the data requires a nanosecond accuracy in the time calibration. A procedure for relative time calibration of the photomultiplier tubes contained in each optical module is described. This procedure is based on the measured coincidences produced in the sea by the
40
K background light and can easily be expanded to a detector with several thousands of optical modules. The time offsets between the different optical modules are obtained using LED nanobeacons mounted inside them. A set of data corresponding to 600 h of livetime was analysed. The results show good agreement with Monte Carlo simulations of the expected optical background and the signal from atmospheric muons. An almost background-free sample of muons was selected by filtering the time correlated signals on all the three optical modules. The zenith angle of the selected muons was reconstructed with a precision of about 3
∘
.
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