455 results on '"Cygnus A"'
Search Results
2. The X-ray ribs within the cocoon shock of Cygnus A.
- Author
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Duffy, R. T., Worrall, D. M., Birkinshaw, M., Nulsen, P. E. J., Wise, M. W., de Vries, M. N., Snios, B., Mathews, W. G., Perley, R. A., Hardcastle, M. J., Rafferty, D. A., McNamara, B. R., Edge, A. C., McKean, J. P., Carilli, C. L., Croston, J. H., Godfrey, L. E. H., and Laing, R. A.
- Subjects
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X-rays , *ACTIVE galaxies , *CYGNUS A , *GAS air conditioning - Abstract
We use new and archival Chandra observations of Cygnus A, totalling ~1.9Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon shock and exhibiting a rib-like structure.We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly 2 x 1010Mʘ. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
3. On the maximum energy of non-thermal particles in the primary hotspot of Cygnus A.
- Author
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Araudo, Anabella T., Bell, Anthony R., Blundell, Katherine M., and Matthews, James H.
- Subjects
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TURBULENCE , *MAGNETIC fields , *PARTICLE acceleration , *CYGNUS A , *SHOCK waves - Abstract
We study particle acceleration and magnetic field amplification in the primary hotspot in the north-west jet of radiogalaxy Cygnus A. By using the observed flux density at 43 GHz in a well-resolved region of this hotspot, we determine the minimum value of the jet density and constrain the magnitude of the magnetic field. We find that a jet with density greater than 5 × 10-5 cm-3 and hotspot magnetic field in the range 50-400 μG are required to explain the synchrotron emission at 43 GHz. The upper-energy cut-off in the hotspot synchrotron spectrum is at a frequency ≲5 × 1014 Hz, indicating that the maximum energy of non-thermal electrons accelerated at the jet reverse shock is Ee,max ~ 0.8 TeV in a magnetic field of 100 μG. Based on the condition that the magnetic-turbulence scalelength has to be larger than the plasma skin depth, and that the energy density in non-thermal particles cannot violate the limit imposed by the jet kinetic luminosity, we show that Ee,max cannot be constrained by synchrotron losses as traditionally assumed. In addition to that, and assuming that the shock is quasi-perpendicular, we show that non-resonant hybrid instabilities generated by the streaming of cosmic rays with energy Ee,max can grow fast enough to amplify the jet magnetic field up to 50-400 μG and accelerate particles up to the maximum energy Ee,max observed in the Cygnus A primary hotspot. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
4. Locating Radio Sources with the Moon.
- Author
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Clarke, R. W.
- Subjects
RADIO sources (Astronomy) ,RADIO astronomy ,CYGNUS A ,LUNAR eclipses ,OCCULTATIONS (Astronomy) - Abstract
The article investigates the observation that celestial radio sources emit radio waves. The study of the sources of radio waves began with the recognition of the source named Cygnus A in 1946. One of the major breakthroughs in study of radio sources was the occurrence of a series of occultations or eclipses of one of the strongest radio sources by the moon which could be observed from Parkes in Australia.
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- 1966
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5. Colliding Galaxies.
- Author
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Minkowski, Rudolph
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CYGNUS A ,BINARY stars ,GALAXY formation ,RADIO sources (Astronomy) ,GALACTIC X-ray sources - Abstract
The article studies the galactic collision in Cygnus A. There was indication that in Cygnus A scientists are beholding a close collision between two galaxies. In an encounter between two galaxies, the gravitational attraction of their stars will perturb the stars' motions and distort the structure of the galaxies, but the stars themselves would not be expected to undergo any observable change.
- Published
- 1956
- Full Text
- View/download PDF
6. The Disk-Driven Jet of Cygnus A.
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Boccardi, Bia, Krichbaum, Thomas P., and Bach, Uwe
- Subjects
REDSHIFT ,RADIO galaxies ,CYGNUS A ,SCHWARZSCHILD radius ,BLACK holes - Abstract
Recently published results from VLBI observations at 3 and 7 millimeters of the radio galaxy Cygnus A are reviewed in this article, and discussed within the model of a prominently stratified jet outflow. At the source redshift (z = 0.056), mm-VLBI allows a spatial resolution down to 200 Schwarzschild radii to be achieved, providing an extremely detailed view of the two-sided jet base. Through a study of the kinematic properties of the flow and of its transverse structure, it is shown that the radio emission is produced by an accelerating, mildly relativistic, parabolically expanding disk-wind. The observed transverse stratification, both of the flux density and of the bulk speed, supports the presence of an invisible faster spine close to the jet axis, powered either by the inner regions of the accretion disk or by the spinning black hole. [ABSTRACT FROM AUTHOR]
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- 2017
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7. Cygnus: a psychoeducational group for carers of people with a personality disorder
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Alice Holland, Sharon Prince, and Ruth Sutherland
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Health (social science) ,Psychoeducational group ,Sociology and Political Science ,health care facilities, manpower, and services ,Health Policy ,media_common.quotation_subject ,Public Health, Environmental and Occupational Health ,social sciences ,humanities ,health services administration ,Personality ,Cygnus A ,Psychology ,health care economics and organizations ,media_common ,Clinical psychology - Abstract
National Institute for Health and Care Excellence guidance suggests that carers of individuals with a diagnosis of borderline personality disorder experience high levels of psychological distress, yet few services in the UK offer specific support to this group of carers. This article will describe the development of a psychoeducational carers’ group based on schema theory (Young et al, 2003), including the development of the role of carer experts-by-experience as group co-facilitators. Initial outcome data from the pilot suggest that carers are highly satisfied with the group and that it improves their knowledge, understanding and personal well-being.
- Published
- 2020
8. Influence of Black Hole Spin on the Shape of the Fe Kα Spectral Line: The Case of 3C 405
- Author
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Jovanović P., Jovanović V. Borka, and Borka D.
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galaxies active ,individual 3c 405 ,cygnus a ,xrays ,galaxies ,Astronomy ,QB1-991 - Abstract
Here we analyze how the angular momenta (spins) of black holes in the centers of Active Galactic Nuclei (AGN) affect the shape of the FeK line emitted from their accretion disks. For that purpose, we compared the observed line profile in the case of radio galaxy 3C 405 (Cygnus A) with its profiles, obtained by numerical simulations based on ray-tracing method in the Kerr metric. Our results show that the spins of rotating central black holes of AGN have significant influence on their FeKα line shapes. Also, we found that in the case of Cygnus A the observed line is probably emitted from the innermost region of its slightly inclined accretion disk around very slowly rotating or even stationary central black hole.
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- 2011
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9. Long-rising Type II supernovae from Palomar Transient Factory and Caltech Core-Collapse Project.
- Author
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Taddia, F., Sollerman, J., Fremling, C., Migotto, K., Gal-Yam, A., Armen, S., Duggan, G., Ergon, M., Filippenko, A. V., Fransson, C., Hosseinzadeh, G., Kasliwal, M. M., Laher, R. R., Leloudas, G., Leonard, D. C., Lunnan, R., Masci, F. J., Moon, D. S., Silverman, J. M., and Wozniak, P. R.
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SUPERNOVAE , *CATACLYSMIC variable stars , *GALACTIC X-ray sources , *STELLAR luminosity function , *CYGNUS A - Abstract
Context. Supernova (SN) 1987A was a peculiar hydrogen-rich event with a long-rising (~84 d) light curve, stemming from the explosion of a compact blue supergiant star. Only a few similar events have been presented in the literature in recent decades. Aims. We present new data for a sample of six long-rising Type II SNe (SNe II), three of which were discovered and observed by the Palomar Transient Factory (PTF) and three observed by the Caltech Core-Collapse Project (CCCP). Our aim is to enlarge this small family of long-rising SNe II, characterizing their differences in terms of progenitor and explosion parameters. We also study the metallicity of their environments. Methods. Optical light curves, spectra, and host-galaxy properties of these SNe are presented and analyzed. Detailed comparisons with known SN 1987A-like events in the literature are shown, with particular emphasis on the absolute magnitudes, colors, expansion velocities, and host-galaxy metallicities. Bolometric properties are derived from the multiband light curves. By modeling the earlytime emission with scaling relations derived from the SuperNova Explosion Code (SNEC) models of MESA progenitor stars, we estimate the progenitor radii of these transients. The modeling of the bolometric light curves also allows us to estimate other progenitor and explosion parameters, such as the ejected 56Ni mass, the explosion energy, and the ejecta mass. Results. We present PTF12kso, a long-rising SN II that is estimated to have the largest amount of ejected 56Ni mass measured for this class. PTF09gpn and PTF12kso are found at the lowest host metallicities observed for this SN group. The variety of early lightcurve luminosities depends on the wide range of progenitor radii of these SNe, from a few tens of R⊙ (SN 2005ci) up to thousands (SN 2004ek) with some intermediate cases between 100 R⊙ (PTF09gpn) and 300 R⊙ (SN 2004em). Conclusions. We confirm that long-rising SNe II with light-curve shapes closely resembling that of SN 1987A generally arise from blue supergiant (BSG) stars. However, some of them, such as SN 2004em, likely have progenitors with larger radii (~300 Ro, typical of yellow supergiants) and can thus be regarded as intermediate cases between normal SNe IIP and SN 1987A-like SNe. Some extended red supergiant (RSG) stars such as the progenitor of SN 2004ek can also produce long-rising SNe II if they synthesized a large amount of 56Ni in the explosion. Low host metallicity is confirmed as a characteristic of the SNe arising from compact BSG stars. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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10. Fine structure of the jet from Cygnus A.
- Author
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Matveyenko, L. and Seleznev, S.
- Subjects
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RADIO galaxies , *WAVELENGTHS , *MAGNETIC fields , *PLASMA flow , *ANGULAR momentum (Nuclear physics) , *CYGNUS A - Abstract
The superfine structure of the bipolar outflow from the radio galaxy Cygnus A has been investigated at a wavelength of 2 cm. The surrounding thermal plasma inflows onto the disk and is transferred in a spiral to the center, with the plasma velocity and temperature increasing to relativistic values. The rotating bipolar outflow carries away an excess angular momentum as it is accumulated. The high-velocity central flow is surrounded by parallel chains of components, the tangential directions of the low-velocity flows. Rotation collimates the flow; ring currents, a longitudinal magnetic field, are generated in it. The size of the high-velocity jet exceeds the size of the counterjet by a factor of 3.5 due to the velocity difference: the acceleration of the flow moving along the field and its decelerationwhenmoving in a direction opposite to the magnetic field of the system. The observed features are typical of objects with active nuclei. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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11. Powerful multiphase outflows in the central region of Cygnus A
- Author
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Rogemar A. Riffel
- Subjects
Physics ,Electron density ,010308 nuclear & particles physics ,Radio galaxy ,Star formation ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Position angle ,01 natural sciences ,Astrophysics - Astrophysics of Galaxies ,Luminosity ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Emission spectrum ,Cygnus A ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Line (formation) - Abstract
We use Gemini Near-Infrared Integral Field Spectrograph (NIFS) observations of the inner 3.5$\times$3.5 kpc$^2$ of the radio galaxy Cygnus A to map the gas excitation and kinematics at a spatial resolution of 200 pc. The emission of the ionised gas shows a biconical morphology, with half-opening angle of 45$^\circ$ and oriented along the position angle of the radio jet. Coronal line emission is seen within the cone, up to 1.75 kpc from the nucleus, with higher ionisation gas observed in the easterly side. The H$_2$ and [Fe II] emission lines are consistent with excitation by the central AGN, with some contribution of shocks to the southwest of the nucleus. The gas visual extinction and electron density are larger than those from optical-based measurements, consistent with the fact that near-IR observations penetrate deeply into the gas emission structure, probing denser and more obscured regions. The gas kinematics shows two components: (i) a rotating disc with kinematic position angle of $\Psi_0=21^\circ\pm2^\circ$, seen both in ionised and molecular gas, and (ii) outflows with velocities of up to 600 kms$^{-1}$ observed within the ionisation cone in ionised gas and restricted to inner 0.5 arcsec in molecular gas. The mass outflow rate in ionised gas is in the range $\sim100-280 {\rm M_\odot yr^{-1}}$ and the kinetic power of the outflow corresponds to 0.3-3.3 per cent of the AGN bolometric luminosity, indicating that the outflows in Cygnus A may be effective in suppressing star formation., Comment: 13 pages, Published in MNRAS, DOI: 10.1093/mnras/stab1877, Version with corrections in the axes labels of some figures
- Published
- 2021
12. Cosmology with powerful radio-loud AGNs
- Author
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Ross J. Turner and Stanislav S. Shabala
- Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Astrophysics::High Energy Astrophysical Phenomena ,Cosmic microwave background ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,7. Clean energy ,01 natural sciences ,symbols.namesake ,0103 physical sciences ,Cygnus A ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,010308 nuclear & particles physics ,Cosmic distance ladder ,Astronomy and Astrophysics ,Quasar ,Comoving distance ,Astrophysics - Astrophysics of Galaxies ,Redshift ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,symbols ,Baryon acoustic oscillations ,Astrophysics - Cosmology and Nongalactic Astrophysics ,Hubble's law - Abstract
Immensely bright quasars and radio-loud active galactic nuclei (AGNs) provide an enticing opportunity to construct standard candles detectable up to the very early universe. An analytic theory is proposed to measure the distance to powerful \citeauthor{FR+1974} type-II radio sources based on their integrated flux density across a broad range of radio frequencies, and the angular size and axis ratio of their synchrotron-emitting lobes. This technique can be used at low-redshift to construct absolute standard candles in conjunction with X-ray observations of the host cluster, or at high-redshift to measure the relative distances of objects and constrain the curvature of our universe. Distances calculated with this method are consistent for dissimilar objects at the same redshift; the two lobes of Cygnus A have flux densities, linear sizes and spectral break frequencies varying by between 15-35\% yet their fitted distances are the same to within 7\%. These distance estimates together yield a transverse comoving distance to Cygnus A of $261_{-55}^{+70}\rm\, Mpc$ corresponding to a Hubble constant of $H_0 = 64_{-13}^{+17}\rm\, km\, s^{-1}\, Mpc^{-1}$. Large samples of suitable FR-II sources could provide a measure of the Hubble constant independent of existing techniques such as the cosmic microwave background, baryon acoustic oscillations, and type 1a supernovae., Comment: 12 pages, 3 figures, 3 tables; accepted in MNRAS
- Published
- 2019
13. Simulations of the merging cluster of galaxies Cygnus A
- Author
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J. M. F. Donnert, Timo Halbesma, M. N. de Vries, Michael W. Wise, and High Energy Astrophys. & Astropart. Phys (API, FNWI)
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Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Active galactic nucleus ,010308 nuclear & particles physics ,Cluster state ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Mass ratio ,01 natural sciences ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Space and Planetary Science ,Intracluster medium ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Cluster (physics) ,Cygnus A ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,Galaxy cluster ,Astrophysics::Galaxy Astrophysics - Abstract
The archetype FR-II galaxy Cygnus A lies in a moderately rich cluster about to undergo a major merger. We study the pre-merger Cygnus cluster environment using smoothed particle hydrodynamics simulations constrained by 2Ms of Chandra observations of the hot intracluster medium. The observations constrain the total gravitating mass and concentration parameter, and the simulations provide the quiescent and merger-enhanced temperature profiles of the pre- and post-merger of the cluster excluding the central active galactic nucleus (AGN). We present the first detailed model of the sub cluster north west of Cygnus A, named CygNW. We find a lower baryon fraction and higher concentration parameter for CygA than expected from known scaling relations in the literature. The model suggests the Cygnus cluster hosts a pre-merger with a progenitor mass ratio of about 1.5:1 at the virial radius. We notice that the intra cluster medium is heated as a result of the merger, but we find no evidence for a (pre-)merger shock in the interstitial region between both cluster haloes. We attribute the merger-induced heating to compression of the cluster outskirts. The smooth model obtained from our simulations is subtracted from the observed cluster state and shows residual temperature structure that is neither hydrostatic nor merger-heated cluster gas. We speculate that this residual heating may result from previous AGN activity over the last ∼100 Myr.
- Published
- 2019
14. ON THE INFLUENCE OF MHD TURBULENCE ON THE STRUCTURE OF THE RADIOGALAXY LOBES
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N. O. Tsvyk
- Subjects
Physics ,Entrainment (hydrodynamics) ,Turbulence ,Radio galaxy ,lcsh:Astronomy ,Astrophysics::High Energy Astrophysical Phenomena ,radio galaxy ,lobes ,FRII ,Cygnus A ,FRI ,M87 ,cosmic rays ,magnetic field ,MHD turbulence ,transport of CRs ,diffusion ,Cosmic ray ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Magnetic field ,Vortex ,lcsh:QB1-991 ,Astrophysics::Solar and Stellar Astrophysics ,Magnetohydrodynamics ,Astrophysics::Galaxy Astrophysics - Abstract
There is considered the evolution of the shape for the radio galaxy lobes of FRI and FRII types from the point of view on changing the configuration of large-scale structure of magnetic field, and energy transport in the turbulent MHD waves. There have been studied the interaction and transformation of waves in the active regions of the lobes, and so studied the role of MHD waves and vortexes in media-mixing processes and in the amplification of the average magnetic field. The transport of low-energy e-CRs responsible for the radio emission in the MHz band (recorded at the UTR-2 and GURT telescopes) is analyzed for the sources like to the Cygnus A and M87. It is shown that the transport of e-CRs mainly corresponds to the diffusion of CRs on MHD and turbulence scatter, and the entrainment of CRs by quasi-regular post-jet flows inside to the lobe. So, the MHz radio emission that observed emphasizes the peculiarities in the lobe which arising when the magnetic field is in reorganization.
- Published
- 2018
15. Cygnus A jointly calibrated and imaged via non-convex optimisation from VLA data
- Author
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Richard A. Perley, Arwa Dabbech, Audrey Repetti, Yves Wiaux, and Oleg Smirnov
- Subjects
Physics ,Radio galaxy ,FOS: Physical sciences ,020206 networking & telecommunications ,Astronomy and Astrophysics ,Context (language use) ,02 engineering and technology ,Inverse problem ,01 natural sciences ,Jansky ,Interferometry ,Space and Planetary Science ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,S band ,Antenna (radio) ,Astrophysics - Instrumentation and Methods for Astrophysics ,Cygnus A ,010303 astronomy & astrophysics ,Algorithm ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,High dynamic range - Abstract
Radio interferometric (RI) data are noisy under-sampled spatial Fourier components of the unknown radio sky affected by direction-dependent antenna gains. Failure to model these antenna gains accurately results in a radio sky estimate with limited fidelity and resolution. The RI inverse problem has been recently addressed via a joint calibration and imaging approach which consists in solving a non-convex minimisation task, involving suitable priors for the DDEs, namely temporal and spatial smoothness, and sparsity for the unknown radio map via an $\ell_1$-norm prior, in the context of realistic RI simulations. Building on these developments, we propose to promote sparsity of the radio map via a log-sum prior, enforcing sparsity more strongly than the $\ell_1$-norm. The resulting minimisation task is addressed via a sequence of non-convex minimisation tasks composed of re-weighted $\ell_1$ image priors, which are solved approximately. We demonstrate the efficiency of the approach on RI observations of the celebrated radio galaxy Cygnus~A obtained with the Karl G. Jansky Very Large Array at X, C, and S bands. More precisely, we showcase that the approach enhances data fidelity significantly while achieving high resolution high dynamic range radio maps, confirming the suitability of the priors considered for the unknown DDEs and radio image. As a clear qualitative indication of the high fidelity achieved by the data and the proposed approach, we report the detection of three background sources in the vicinity of Cyg~A, at S band., Comment: 22 pages,13 figures. Submitted to MNRAS
- Published
- 2021
- Full Text
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16. Phenomenological model for the evolution of radio galaxies such as Cygnus A.
- Author
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Artyukh, V.
- Subjects
- *
RADIO galaxies , *PHENOMENOLOGICAL theory (Physics) , *MATHEMATICAL models , *STAR formation , *COSMOLOGICAL distances , *CYGNUS A - Abstract
A phenomenological model for the evolution of classical radio galaxies such as Cygnus A is presented. An activity cycle of the host galaxy in the radio begins with the birth of radio jets, which correspond to shocks on scales ∼1 pc (the radio galaxy B0108+388). In the following stage of the evolution, the radio emission comes predominantly from formations on scales of 10-100 pc, whose physical parameters are close to those of the hot spots of Cygnus A (this corresponds to GHz-peaked spectrum radio sources). Further, the hot spots create radio lobes on scales of 10-10 pc (compact steep-spectrum radio sources). The fully formed radio galaxies have radio jets, hot spots, and giant radio lobes; the direction of the jets can vary in a discrete steps with time, creating new hot spots and inflating the radio lobes (as in Cygnus A). In the final stage of the evolutionary cycle, first the radio jets disappear, then the hot spots, and finally the radio lobes (similar to the giant radio galaxies DA 240 and 3C 236). A large fraction of radio galaxies with repeating activity cycles is observed. The close connection between Cygnus A-type radio galaxies and optical quasars is noted, as well as similarity in the cosmological evolution of powerful radio galaxies and optical quasars. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
17. Multiwavelength study of Cygnus A.
- Author
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Pyrzas, S., Steenbrugge, K. C., and Blundell, K. M.
- Subjects
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CYGNUS A , *ACTIVE galactic nuclei , *RADIO galaxies , *RADIO jets (Astrophysics) , *STELLAR magnetic fields , *STELLAR luminosity function - Abstract
Context. The jets in Faranoff-Riley type II AGN are supposed come to an abrupt halt in hotspots on opposite sides of the nucleus. Quite commonly, two hotspots are observed in each lobe. The origin of the second hotspot is currently poorly understood. Aims. Our aims are to determine the origin of the secondary hotspot in the western lobe of Cygnus A from high resolution multifrequency radio images; to determine the minimum Lorentz factor of the electrons in the hotspots, often referred to as the low-energy turnover; and to study the magnetic field configuration of the hotspots. Methods. We used 151 MHz Merlin and 327 MHz, 1.4, 5, 8, 15, and 43 GHz VLA images to determine the centroid of the peak luminosity, the spectral shape, and polarization fraction of both hotspots in the western lobe of Cygnus A. Results. We find a spatial shift in peak luminosity between the lower and higher frequency images for both hotspots. We determine the minimum Lorentz factor of the electrons to be ~1000, and show that most of the emission from the primary hotspot is linearly polarized. The minimum energy magnetic field strength is found to range between ~0.14 and ~0.5mG in both the primary and secondary hotspots. Conclusions. From the low polarization and the determined outflow velocity, we conclude that the secondary hotspot is no longer a strong shock, and is an expanding, and hence a fading hotspot. This hotspot has an age that is of the same order of magnitude as the jet precession period. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
18. The White Dwarf in SS Cygni and Related Topics: FUSE + HST Spectral Analysis.
- Author
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Sion, Edward M., Godon, Patrick, Myszka, Janine, and Blair, William P.
- Subjects
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WHITE dwarf stars , *VACUUM ultraviolet spectroscopy , *ACCRETION (Astrophysics) , *SPECTRAL energy distribution , *COOLING , *DWARF novae , *STARBURSTS , *VARIABLE stars , *CYGNUS A - Abstract
We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. From the best-fit model solutions to the combined HST +FUSE spectral energy distribution, we find that the white dwarf is reaching a temperature Teff≈45-55,000 K in quiescence, assuming log(g) = 8.3 with a solar composition accreted atmosphere. We discuss two challenges to understanding the cooling of a white dwarf in response to heating by a dwarf nova accretion event. We present the most recent distribution of white dwarf temperatures versus orbital period in the context of the time-averaged accretion rate and long term compressional heating models. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
19. A radio and near-infrared mini-survey of the MGRO J2019+37 complex.
- Author
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Paredes, J. M., Martí, J., Ishwara-Chandra, C. H., Sánchez-Sutil, J. R., Muñoz-Arjonilla, A. J., Zabalza, V., Ribó, M., Luque-Escamilla, P. L., Bosch-Ramon, V., Peracaula, M., Moldón, J., and Bordas, P.
- Subjects
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GAMMA rays , *RADIO telescopes , *CYGNUS A , *ASTRONOMICAL observatories , *INFRARED technology - Abstract
MGRO J2019+37 is an unidentified source of very high energy gamma-rays originally reported by the MILAGRO collaboration as the brightest TeV source in the Cygnus region. Despite the poor angular resolution of MILAGRO, this object seems to be most likely an extended source or, alternatively, a superposition of point-like TeV sources. In order to contribute to the understanding of this peculiar object, we have mosaiced it with the Giant Metrewave Radio Telescope (GMRT) in Pune, India, at the 610 MHz frequency covering a field of view of about 6 square degrees down to a typical rms noise of a few tenths of mJy. We also observed the central square degree of this mosaic in the near infrared Ks-band using the 3.5 m telescope and the OMEGA2000 camera at the Calar Alto observatory (Spain). We present here a first account of our observations and results, together with a preliminar cross correlation of the radio and infrared source catalog as well as a correlation with the available X-ray observations of the region. [ABSTRACT FROM AUTHOR]
- Published
- 2008
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20. Hubble & Eddington.
- Author
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Gondhalekar, Prabhakar
- Abstract
Gravity is the only truly universal force. It moulded the universe and it almost certainly will overwhelmingly determine the end of the universe. Today we also know (certainly believe) that gravitation is primarily responsible for the formation of the large structures we see around us: the Earth, the solar system, the stars, and the galaxies. Gravity has fashioned the beautiful and awe-inspiring sights in the sky, which have inspired both philosophers and mystics. Without gravity the sky would have been a very boring sight. Even more exotic objects, only visible at radio, X-ray or other energies, are present in the sky and these have also been fashioned by gravity. After the formation of the solar system, gravity has played a benign role in the evolution of life in the solar system. The strong gravity of Jupiter has shielded Earth from destructive impacts by comets and asteroids, and it is reasonable to say that life on Earth would not have survived without this ‘gravity shield’. It is for this reason that there is such excitement at the discovery of large planets around other stars. Life, as we know it, may not (almost certainly does not) exist on these large planets, but without such a large planet and its gravity shield, life certainly would not survive and flourish on an inner planet if there is one. In this chapter the central role of gravity in shaping the universe and even the climate on Earth is described. FIGURES OF PLANETS The sizes and the figures of the planets have been subjects of inquiry and discussion since antiquity. The Greeks accepted the Platonic belief in perfect shapes and believed that the planets, and the Earth in particular, were perfect spheres. [ABSTRACT FROM AUTHOR]
- Published
- 2001
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21. Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus.
- Author
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Steenbrugge, K. C., Blundell, K. M., and Pyrzas, S.
- Subjects
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RADIO galaxies , *ACTIVE galaxies , *GALAXY clusters , *RADIAL velocity of stars , *CYGNUS A - Abstract
Context. Cygnus A, as the nearest powerful FR II radio galaxy, plays an important role in understanding jets and their impact on the surrounding intracluster medium. Aims. We explain why the nucleus is observed superposed onto the eastern lobe rather than in between the two lobes, and why the jet and counterjet are non-colinear. Methods. We made a comparative study of the radio images at different frequencies of Cygnus A, in combination with the published results on the radial velocities in the Cygnus A cluster. Results. From the morphology of the inner lobes we conclude that the lobes are not interacting with one another, but are well separated, even at low radio frequencies. We explain the location of the nucleus as the result of the proper motion of the galaxy through the cluster. The required proper motion is of the same order of magnitude as the radial velocity offset of Cygnus A with the sub-cluster it belongs to. The proper motion of the galaxy through the cluster likely also explains the non-colinearity of the jet and counterjet. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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22. FIRST DYNAMIC COMPUTATIONS OF SYNCHROTRON EMISSION FROM THE CYGNUS A RADIO CAVITY: EVIDENCE FOR ELECTRON PAIR PLASMA IN CAVITY.
- Author
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Mathews, William G.
- Subjects
- *
GALAXIES , *CYGNUS A , *SYNCHROTRON radiation , *HYDRODYNAMICS , *HELIOSPHERE - Abstract
Cosmic rays, thermal gas and magnetic fields in FRII radio cavities are assumed to come entirely from winds flowing from just behind the jet shocks. Combining analytic and computational methods, it is shown that the computed radio-electron energy distribution and synchrotron emissivity spectra everywhere in the Cygnus A radio cavity agree with radio observations of the Cygnus A lobes. The magnetic field energy density is small everywhere and evolves passively in the post-shock wind. Most synchrotron emission arises in recent post-shock material as it flows back along the radio cavity wall. Because it experienced less adiabatic expansion, the magnetic field in this young backflow is larger than elsewhere in the radio lobe, explaining the observed radio synchrotron limb-brightening. The boundary backflow decelerates due to small cavity pressure gradients, causing large-scale fields perpendicular to the backflow (and synchrotron emission) to grow exponentially unlike observations. However, if the field is random on subgrid (sub-kpc) scales, the computed field reproduces both the magnitude and slowly decreasing radio synchrotron emissivity observed along the backflow. The radio synchrotron spectrum and image computed with a small-scale random field agree with Very Large Array observations. The total relativistic energy density in the post-jet shock region required in computations to inflate the radio cavity matches the energy density of relativistic electrons observed in the post-shock region of Cygnus A. This indicates that the component in the jet and cavity that dominates the dynamical evolution is a relativistic pair plasma. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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23. The X-Ray Cavity Around Hotspot E in Cygnus A: Tunneled by a Deflected Jet
- Author
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Amalya C. Johnson, Martijn de Vries, Lerato Sebokolodi, Bradford Snios, Paul Nulsen, Michael W. Wise, Ralph P. Kraft, and Richard A. Perley
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,010504 meteorology & atmospheric sciences ,Radio galaxy ,X-ray ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Lobe ,medicine.anatomical_structure ,Space and Planetary Science ,Intracluster medium ,0103 physical sciences ,Hotspot (geology) ,medicine ,Outflow ,Surface brightness ,Cygnus A ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
The powerful FR II radio galaxy Cygnus A exhibits primary and secondary hotspots in each lobe. A 2 Msec Chandra X-ray image of Cygnus A has revealed an approximately circular hole, with a radius of 3.9 kpc, centered on the primary hotspot in the eastern radio lobe, hotspot E. We infer the distribution of X-ray emission on our line-of-sight from an X-ray surface brightness profile of the radio lobe adjacent to the hole and use it to argue that the hole is excavated from the radio lobe. The surface brightness profile of the hole implies a depth at least 1.7 $\pm$ 0.3 times greater than its projected width, requiring a minimum depth of 13.3 $\pm$ 2.3 kpc. A similar hole observed in the 5 GHz VLA radio map reinforces the argument for a cavity lying within the lobe. We argue that the jet encounters the shock compressed intracluster medium at hotspot E, passing through one or more shocks as it is deflected back into the radio lobe. The orientation of Cygnus A allows the outflow from hotspot E to travel almost directly away from us, creating an elongated cavity, as observed. These results favor models for multiple hotspots in which an FR II jet is deflected at a primary hotspot, then travels onward to deposit the bulk of its power at a secondary hotspot, rather than the dentist drill model., Accepted to ApJ, 12 pages, 7 figures, 5 tables
- Published
- 2020
24. AGN feedback in the FR II galaxy 3C 220.1
- Author
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Mark Birkinshaw, Ming Sun, Christine Jones, William R. Forman, Chong Ge, Craig L. Sarazin, Wenhao Liu, Paul Nulsen, and Diana M Worrall
- Subjects
Active galactic nucleus ,Radio galaxy ,astro-ph.GA ,Astrophysics::High Energy Astrophysical Phenomena ,Inverse ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Luminosity ,0103 physical sciences ,Brightest cluster galaxy ,010306 general physics ,Cygnus A ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,astro-ph.HE ,Astronomy and Astrophysics ,Radius ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
We present results from a deep (174 ks) Chandra observation of the FR-II radio galaxy 3C 220.1, the central brightest cluster galaxy (BCG) of a $kT \sim$ 4 keV cluster at $z=0.61$. The temperature of the hot cluster medium drops from $\sim5.9$ keV to $\sim3.9$ keV at $\sim$ 35 kpc radius, while the temperature at smaller radii may be substantially lower. The central active galactic nucleus (AGN) outshines the whole cluster in X-rays, with a bolometric luminosity of $2.0\times10^{46}$ erg s$^{-1}$ ($\sim10$% of the Eddington rate). The system shows a pair of potential X-ray cavities $\sim35$ kpc east and west of the nucleus. The cavity power is estimated within the range of $1.0\times10^{44}$ erg s$^{-1}$ and $1.7\times10^{45}$ erg s$^{-1}$, from different methods. The X-ray enhancements in the radio lobes could be due to inverse Compton emission, with a total 2-10 keV luminosity of $\sim8.0\times10^{42}$ erg s$^{-1}$. We compare 3C 220.1 with other cluster BCGs, including Cygnus A, as there are few BCGs in rich clusters hosting an FR-II galaxy. We also summarize the jet power of FR-II galaxies from different methods. The comparison suggests that the cavity power of FR-II galaxies likely under-estimates the jet power. The properties of 3C 220.1 suggest that it is at the transition stage from quasar-mode feedback to radio-mode feedback., 14 pages, 13 figures, MNRAS accepted
- Published
- 2020
25. Archival VLBA observations of the Cygnus A Nuclear Radio Transient (Cyg A-2) Strengthen the Tidal Disruption Event Interpretation
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Emil Lenc, Steven Tingay, and James Miller-Jones
- Subjects
Physics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Active galactic nucleus ,010504 meteorology & atmospheric sciences ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Compact star ,01 natural sciences ,Astrophysics - Astrophysics of Galaxies ,Calculation methods ,Luminosity ,Tidal disruption event ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Transient (oscillation) ,Cygnus A ,Astrophysics - High Energy Astrophysical Phenomena ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
We have analyzed archival VLBA data for Cygnus A between 2002 and 2013, to search for radio emission from the transient discovered in 2015 by \citet{per18} approximately 0.4\arcsec~ from the nucleus of Cygnus A (Cyg A-2). \citet{per18} use VLA and VLBA archival data (between 1989 and 1997) to show that the transient rises in flux density by a factor of at least five in less than approximately 20 years. With the additional data presented here, we revise the rise time to between approximately four years and six years, based on a new detection of the source at 15.4 GHz from October 2011. Our results strengthen the interpretation of Cyg A-2 as the result of a Tidal Disruption Event (TDE), as we can identify the location of the compact object responsible for the TDE and can estimate the angular expansion speed of the resulting radio emitting structures, equivalent to an apparent expansion speed of $10^{49}$ erg. Due to the improved temporal coverage of our archival measurements, we find that it is unlikely that Cyg A-2 has previously been in a high luminosity radio state over the last 30 years., Eight pages, three figures, accepted to ApJ Letters
- Published
- 2020
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26. Cassiopeia A, Cygnus A, Taurus A, and Virgo A at ultra-low radio frequencies
- Author
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F. de Gasperin, J. Vink, J. P. McKean, A. Asgekar, I. Avruch, M. J. Bentum, R. Blaauw, A. Bonafede, J. W. Broderick, M. Brüggen, F. Breitling, W. N. Brouw, H. R. Butcher, B. Ciardi, V. Cuciti, M. de Vos, S. Duscha, J. Eislöffel, D. Engels, R. A. Fallows, T. M. O. Franzen, M. A. Garrett, A. W. Gunst, J. Hörandel, G. Heald, M. Hoeft, M. Iacobelli, L. V. E. Koopmans, A. Krankowski, P. Maat, G. Mann, M. Mevius, G. Miley, R. Morganti, A. Nelles, M. J. Norden, A. R. Offringa, E. Orrú, H. Paas, V. N. Pandey, M. Pandey-Pommier, R. Pekal, R. Pizzo, W. Reich, A. Rowlinson, H. J. A. Rottgering, D. J. Schwarz, A. Shulevski, O. Smirnov, C. Sobey, M. Soida, M. Steinmetz, M. Tagger, M. C. Toribio, A. van Ardenne, A. J. van der Horst, M. P. van Haarlem, R. J. van Weeren, C. Vocks, O. Wucknitz, P. Zarka, P. Zucca, Astronomy, Kapteyn Astronomical Institute, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), De Gasperin F., Vink J., McKean J.P., Asgekar A., Avruch I., Bentum M.J., Blaauw R., Bonafede A., Broderick J.W., Bruggen M., Breitling F., Brouw W.N., Butcher H.R., Ciardi B., Cuciti V., De Vos M., Duscha S., Eisloffel J., Engels D., Fallows R.A., Franzen T.M.O., Garrett M.A., Gunst A.W., Horandel J., Heald G., Hoeft M., Iacobelli M., Koopmans L.V.E., Krankowski A., Maat P., Mann G., Mevius M., Miley G., Morganti R., Nelles A., Norden M.J., Offringa A.R., Orru E., Paas H., Pandey V.N., Pandey-Pommier M., Pekal R., Pizzo R., Reich W., Rowlinson A., Rottgering H.J.A., Schwarz D.J., Shulevski A., Smirnov O., Sobey C., Soida M., Steinmetz M., Tagger M., Toribio M.C., Van Ardenne A., Van Der Horst A.J., Van Haarlem M.P., Van Weeren R.J., Vocks C., Wucknitz O., Zarka P., Zucca P., High Energy Astrophys. & Astropart. Phys (API, FNWI), Gravitation and Astroparticle Physics Amsterdam, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES)
- Subjects
Astronomy ,media_common.quotation_subject ,Astrophysics::High Energy Astrophysical Phenomena ,radio continuum: general ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,radio continuum ,law.invention ,Telescope ,law ,0103 physical sciences ,Angular resolution ,[PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det] ,Surface brightness ,010306 general physics ,Cygnus A ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,media_common ,High Energy Astrophysical Phenomena (astro-ph.HE) ,[PHYS]Physics [physics] ,Physics ,[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph] ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy and Astrophysics ,LOFAR ,Astrophysics - Astrophysics of Galaxies ,interferometric [techniques] ,Cassiopeia A ,techniques: interferometric ,13. Climate action ,Space and Planetary Science ,Sky ,general ,Astrophysics of Galaxies (astro-ph.GA) ,interferometric ,ddc:520 ,general [radio continuum] ,Radio frequency ,Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics - Instrumentation and Methods for Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,techniques ,general [ontinuum] - Abstract
The four persistent radio sources in the northern sky with the highest flux density at metre wavelengths are Cassiopeia A, Cygnus A, Taurus A, and Virgo A; collectively they are called the A-team. Their flux densities at ultra-low frequencies (, 7 pages, 2 figures, accepted A&A, online data on A&A website
- Published
- 2020
27. First results of radio observations of the sun and powerful discrete radio sources using the Irkutsk Radar.
- Author
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Vasil'ev, R., Kushnarev, D., Kashapova, L., Lebedev, V., Medvedev, A., Nevedimov, N., and Ratovskii, K.
- Subjects
- *
ASTRONOMICAL observations , *RADIO sources (Astronomy) , *RADAR , *SCATTERING (Physics) , *IONOSPHERE , *CORONAL mass ejections , *CYGNUS A - Abstract
Using the Irkutsk Incoherent Scattering Radar, it is demonstrated that the high sensitivity of such radars, which are usually used for studies of the Earth's ionosphere, also enables their use in a passive mode for observations of astronomical radio sources. Observations of solar flares accompanied by coronal mass ejections and of quasi-stationary radio sources on the Sun have been carried out. In addition, scintillations of several of the brightest discrete radio sources (Cygnus A, Cassiopeia A, and the Crab Nebula) have been studied over several months. These data can also be useful for studies of the ionosphere and interplanetary space. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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28. How frequent are close supermassive binary black holes in powerful jet sources?
- Author
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Alexander Wagner, Hans Böhringer, Marc Sarzi, Geoffrey V. Bicknell, Martin Krause, Gayoung Chon, Stanislav S. Shabala, Martin J. Hardcastle, and Mohammad Ali Nawaz
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Supermassive black hole ,010308 nuclear & particles physics ,Gravitational wave ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Jansky ,Binary black hole ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Physics::Space Physics ,0103 physical sciences ,Precession ,Astrophysics - High Energy Astrophysical Phenomena ,Blazar ,Cygnus A ,010303 astronomy & astrophysics ,Geodetic effect - Abstract
Supermassive black hole binaries may be detectable by an upcoming suite of gravitational wave experiments. Their binary nature can also be revealed by radio jets via a short-period precession driven by the orbital motion as well as the geodetic precession at typically longer periods. We have investigated Karl G. Jansky Very Large Array (VLA) and MERLIN radio maps of powerful jet sources for morphological evidence of geodetic precession. For perhaps the best studied source, Cygnus A, we find strong evidence for geodetic precession. Projection effects can enhance precession features, for which we find indications in strongly projected sources. For a complete sample of 33 3CR radio sources we find strong evidence for jet precession in 24 cases (73 per cent). The morphology of the radio maps suggests that the precession periods are of the order of 10^6 - 10^7 yr. We consider different explanations for the morphological features and conclude that geodetic precession is the best explanation. The frequently observed gradual jet angle changes in samples of powerful blazars can be explained by orbital motion. Both observations can be explained simultaneously by postulating that a high fraction of powerful radio sources have sub-parsec supermassive black hole binaries. We consider complementary evidence and discuss if any jetted supermassive black hole with some indication of precession could be detected as individual gravitational wave source in the near future. This appears unlikely, with the possible exception of M87., Comment: 24 pages, 36 figures, accepted by MNRAS
- Published
- 2018
29. Non-thermal emission in lobes of radio galaxies: III. 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236
- Author
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Yoel Rephaeli and Massimo Persic
- Subjects
High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Radio galaxy ,Astrophysics::High Energy Astrophysical Phenomena ,Cosmic microwave background ,Compton scattering ,FOS: Physical sciences ,Astronomy and Astrophysics ,Electron ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Radiation ,Extragalactic background light ,Space and Planetary Science ,Cygnus A ,Astrophysics - High Energy Astrophysical Phenomena ,Astrophysics::Galaxy Astrophysics ,Fermi Gamma-ray Space Telescope - Abstract
Recent analyses of the broad spectral energy distributions (SED) of extensive lobes of local radio-galaxies have confirmed the leptonic origin of their Fermi/LAT gamma-ray emission, significantly constraining the level of hadronic contribution. SED of distant (D > 125 Mpc) radio-galaxy lobes are currently limited to the radio and X-ray bands, hence give no information on the presence of non-thermal (NT) protons but are adequate to describe the properties of NT electrons. Modeling lobe radio and X-ray emission in 3C 98, Pictor A, DA 240, Cygnus A, 3C 326, and 3C 236, we fully determine the properties of intra-lobe NT electrons and estimate the level of the related gamma-ray emission from Compton scattering of the electrons off the superposed Cosmic Microwave Background, Extragalactic Background Light, and source-specific radiation fields., 8 pages, 4 figures; a few typos corrected; several missing references added
- Published
- 2019
30. The X-ray ribs within the cocoon shock of Cygnus A
- Author
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Alastair C. Edge, Bradford Snios, Michael W. Wise, William G. Mathews, Robert Laing, Martin J. Hardcastle, Paul Nulsen, Ryan T. Duffy, M. N. de Vries, Leith Godfrey, Chris Carilli, D. Rafferty, Mark Birkinshaw, Judith H. Croston, Richard A. Perley, Brian R. McNamara, John McKean, Diana M Worrall, High Energy Astrophys. & Astropart. Phys (API, FNWI), and Sterrenkunde
- Subjects
active [Galaxies] ,Astrophysics::High Energy Astrophysical Phenomena ,galaxies: active ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,galaxies: individual: Cygnus A ,0103 physical sciences ,Cluster (physics) ,Cygnus A ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,radio continuum: galaxies ,Jet (fluid) ,Shock (fluid dynamics) ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Debris ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,galaxies [X-rays] ,Core (optical fiber) ,Temperature gradient ,X-rays: galaxies ,galaxies: active, galaxies: individual: Cygnus A, radio continuum: galaxies, X-rays: galaxies, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,individual: Cygnus A- radio continuum: galaxies [Galaxies] ,Astrophysics - High Energy Astrophysical Phenomena - Abstract
We use new and archival Chandra observations of Cygnus A, totalling $\sim$1.9 Ms, to investigate the distribution and temperature structure of gas lying within the projected extent of the cocoon shock and exhibiting a rib-like structure. We confirm that the X-rays are dominated by thermal emission with an average temperature of around 4 keV, and have discovered an asymmetry in the temperature gradient, with the southwestern part of the gas cooler than the rest by up to 2 keV. Pressure estimates suggest that the gas is a coherent structure of single origin located inside the cocoon, with a mass of roughly $2\times10^{10} M_{\odot}$. We conclude that the gas is debris resulting from disintegration of the cool core of the Cygnus A cluster after the passage of the jet during the early stages of the current epoch of activity. The 4 keV gas now lies on the central inside surface of the hotter cocoon rim. The temperature gradient could result from an offset between the centre of the cluster core and the Cygnus A host galaxy at the switch-on of current radio activity., 15 pages, 12 figures, accepted by MNRAS
- Published
- 2018
31. Cygnus A super-resolved via convex optimization from VLA data
- Author
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Richard A. Perley, Arwa Dabbech, Alexandru Onose, Oleg Smirnov, Abdullah Abdulaziz, and Yves Wiaux
- Subjects
Physics ,Regular polygon ,FOS: Physical sciences ,020206 networking & telecommunications ,Astronomy and Astrophysics ,02 engineering and technology ,Iterative reconstruction ,01 natural sciences ,Jansky ,High fidelity ,Space and Planetary Science ,0103 physical sciences ,Convex optimization ,Prior probability ,0202 electrical engineering, electronic engineering, information engineering ,Leverage (statistics) ,Astrophysics - Instrumentation and Methods for Astrophysics ,Cygnus A ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,010303 astronomy & astrophysics ,Algorithm - Abstract
We leverage the Sparsity Averaging Reweighted Analysis (SARA) approach for interferometric imaging, that is based on convex optimisation, for the super-resolution of Cyg A from observations at the frequencies 8.422GHz and 6.678GHz with the Karl G. Jansky Very Large Array (VLA). The associated average sparsity and positivity priors enable image reconstruction beyond instrumental resolution. An adaptive Preconditioned Primal-Dual algorithmic structure is developed for imaging in the presence of unknown noise levels and calibration errors. We demonstrate the superior performance of the algorithm with respect to the conventional CLEAN-based methods, reflected in super-resolved images with high fidelity. The high resolution features of the recovered images are validated by referring to maps of Cyg A at higher frequencies, more precisely 17.324GHz and 14.252GHz. We also confirm the recent discovery of a radio transient in Cyg A, revealed in the recovered images of the investigated data sets. Our matlab code is available online on GitHub., Comment: 14 pages, 7 figures (3/7 animated figures), accepted for publication in MNRAS
- Published
- 2018
32. Physical conditions in the hot spots of the radio galaxy Cygnus A.
- Author
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Artyukh, V., Tyul'bashev, S., and Chernikov, P.
- Subjects
- *
HOT spots (Astronomy) , *STELLAR magnetic fields , *STELLAR evolution , *SYNCHROTRON radiation , *DISTRIBUTION of stars , *CYGNUS A - Abstract
It is shown that composite radio spectra of the hot spots of the radio galaxy Cygnus A can be fully explained by assuming a nonuniform distribution of the magnetic fields inside the hot spots, without invoking any physical mechanisms other than synchrotron radiation. The magnetic fields are strong ( B ∼ 10−10 G) at the center of the hot spots, and decreases at the hot-spot edges to the level of the magnetic field of the radio lobes in which the hot spots are embedded ( B ∼ 10−10 G). The difference in the magnetic field between the hot-spot center and edge decreases during the evolution, while the average magnetic-field intensity increases. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
33. The influence of radio astronomy on cosmology.
- Abstract
It is a privilege to participate – along with a number of those who played leading parts in the discoveries being commemorated – in this notable celebration. At the same time I do have the feeling of being dug up as a fossil theorist in order to illustrate one aspect of the developments concerned. Anyhow, my rôle is to try to bring alive the atmosphere of those years when radio astronomy first entered the field of cosmology with unexpected and exciting consequences. For other reasons as well, this was a time of crucial developments in cosmology. Since I have both to sketch in the background, as well as bring out highlights in the foreground, I necessarily give a picture without much detail. I begin with a review of developments in cosmology from the time of Hubble to the early 1950s, and then discuss the influence of radio astronomy. Such detail as I do give will be subject to much selection, largely because much of the action with which I am best acquainted took place in Cambridge and in the Royal Astronomical Society. COSMOLOGY OF THE VISIBLE UNIVERSE In 1929 Edwin Hubble began to publish his observational discovery of the expansion of the universe. I shall proceed on the assumption that the expansion is real in the most ordinary sense. Hubble found that for any remote galaxy where for the given epoch of observation H
0 is a constant, the same for all galaxies. Hubble established his distance scale by a number of steps, all but the first and shortest employing standard candles of one sort or another. [ABSTRACT FROM AUTHOR]- Published
- 1984
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- View/download PDF
34. The development of aperture synthesis at Cambridge.
- Abstract
By the beginning of 1954 the principles of aperture synthesis were fully understood all over the world, but the world of radio astronomy was then very small, and the world I mean, in which radio astronomy was controlled by radio engineers who were learning astronomy, was smaller still. In the Netherlands and in the United States radio astronomy was in the hands of real astronomers, to whom a telescope meant a paraboloidal mirror and nothing else; their contributions were of a different kind. So the little world that understood aperture synthesis consisted of CSIRO Radiophysics Division in Sydney, the English radio astronomers at Cambridge and Manchester, and the French group at Nançay. Furthermore, the Manchester group were preoccupied with building a very large paraboloid indeed, so they were not very interested. The underlying principles were neatly written down by Bracewell and Roberts (1954). I wrote them down too, but only in my thesis (Scheuer 1954), because Martin Ryle took a severe line, that on engineering topics you shouldn't write mere theory, you should jolly well build the thing first. It took ten years to get from the principles to the first full-scale working instrument of the modern kind: the Cambridge one-mile telescope. I don't think that was because we couldn't make the next mental step to earth rotation synthesis. Pat O'Brien had observed the sun with interferometers along various position angles at various times of day (O'Brien 1953), and I had observed the profile of the Milky Way at such time as it makes a vertical arch over Cambridge, so the fact that the earth turns the interferometer had been forced into our consciousness quite hard enough. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
35. Early work on radio stars at Cambridge.
- Abstract
Two powerful influences acted on the early development of radio astronomy at Cambridge. The first was the existing radio research under J.A. Ratcliffe, directed primarily at the ionosphere. J.W. Findlay, who is known amongst radio astronomers as the inspiration for the 300 ft transit telescope at Green Bank and, later, as one of the designers of the Very Large Array, was a member of this research group before and after the 1939–45 war. The second influence was wartime experience in radar, when Martin Ryle in particular developed his genius for experimental methods which were at once bold, original and economical. His most important wartime work was in airborne counter-measures, involving the analysis of enemy radar and the desperate scramble to provide aircraft with warnings of radar-directed fighter attack. Ratcliffe would maintain that his own contribution was to attract Martin Ryle to the Cavendish, and to encourage him to develop his own techniques in investigating radio waves from the sun. Nevertheless Ratcliffe's influence in our understanding of radio, and even more of Fourier analysis, were other vital ingredients. Radio research re-started in the Cavendish in 1945. Ryle, who was an Imperial Chemical Industries Research Fellow, was joined by Derek Vonberg; both were registered for Ph.D.s, although neither ever wrote a thesis. Their first approach to the measurement of solar radio waves was to build a radio version of the Michelson interferometer which would distinguish the sun from other extraneous sources of noise. They built a switched receiver known as the Cosmic Radio Pyrometer (Ryle & Vonberg 1948) in which a controllable noise diode was switched against the input noise signal. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
36. Paraboloids, galaxies and stars: memories of Jodrell Bank.
- Abstract
SOME EARLY WORK WITH THE 218 FT PARABOLOID Introduction I shall always remember reading an article on “Cosmic Static” which Grote Reber published (Reber 1940) in the February 1940 issue of the Proceedings of the Institute of Radio Engineers. It was during World War II and we were working desperately hard on various “advanced” forms of airborne radar for the detection of ships, submarines and aircraft. Reber's strange article was sandwiched in between conventional papers on frequency modulation and negative feedback and, because it was so intriguingly odd, it lay open on our laboratory bench for several days until, inevitably, someone put a hot soldering iron down on it. Reber had worked at much the same frequency (160 MHz) as we had been using for airborne radar for several years, and I couldn't help thinking how nice it would be to turn some of our relatively “superior” equipment on to the sky to see if his “cosmic static” was really there. It was not until nearly a decade later that I was given the opportunity at Jodrell Bank. In 1949 I was a partner in a firm of consulting engineers with Sir Robert Watson-Watt, the pioneer of radar. Sir Robert wanted to move our firm to Canada – which he did with disastrous results – and I did not. Instead I decided to stop advising firms on research and do some myself, perhaps in a University. As a start I went to see my old friend and wartime colleague F.C. Williams in Manchester; he suggested that I should take a look at what Bernard Lovell was doing at Jodrell Bank. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
37. The origins and early history of Jodrell Bank.
- Abstract
WORLD WAR II INFLUENCES The observatory at Jodrell Bank emerged in a most unusual manner from my research work as a young man on cosmic rays. In the years immediately before the outbreak of World War II, I was on the staff of the Physics Department of the University of Manchester as an Assistant Lecturer. Originally I continued my researches on the electrical conductivity of thin films, which I had worked on as a postgraduate student in Bristol, but when P.M.S. Blackett succeeded W.L. Bragg as the Professor of Physics in 1937 I eagerly seized the opportunity of joining him in his cosmic ray researches. I took over from a young Chinese, Hu Chien Shan (who had returned to China to help in the war against Japan), and modernised an automatic counter-controlled cloud chamber. With this device I first studied the cosmic ray showers produced by the newly discovered particles, the ‘heavy’ electrons, then called mesotrons, later mesons and now recognised as the mu-meson or muon. With L. Jánossy (Jánossy & Lovell 1938) and J.G. Wilson (Lovell & Wilson 1939) I was using this device to investigate the extensive cosmic ray air showers in 1939. In the later stages of this work we were using two cloud chambers separated by 20 metres to photograph showers which we estimated to have energies approaching 10
16 eV. At that time the energy spectrum had been established only to about 1010 eV, and there was little information about the spectrum at higher energies or about the upper limit of the energy range. [ABSTRACT FROM AUTHOR]- Published
- 1984
- Full Text
- View/download PDF
38. Radio sources and the log N–log S controversy.
- Abstract
The Sydney-Cambridge controversies of the 1950s concerning the nature of radio sources and their role in cosmology remain of interest because the roots of the controversies appear to lie in differing philosophies of scientific research as much as in observational discrepancies. They also clearly show the influence of instrumental limitations of the time on the beliefs of astronomers and thus contain a message for the new generation. The controversies have been discussed at length by Edge & Mulkay (1976) but there remains a great deal which can be said. Edge & Mulkay aimed to give an objective account but did not have direct access to Australian material or contact with those of us involved in the controversies. Here I try to present my personal viewpoint of the time, as much, that is, as I am now able to reconstruct. My uncertain memory of some of these ancient events has been bolstered by access to the correspondence files of the Division of Radiophysics, with the kind permission of Dr. R.H. Frater, Chief of the Division. EARLY YEARS Nowadays it is difficult to appreciate the abysmal ignorance of the nature of radio sources prevalent around 1950. We were struggling with inadequate instruments to make physical sense of some completely new and unexpected phenomena. There were but two types of instrument, interferometers comprising pairs of low directivity antennas (or the equivalent single antenna on a cliff-top overlooking the sea) and single small-size antennas operating at low frequencies with poor resolution. Accordingly, the sky appeared to be populated by randomly distributed ‘point sources’, which produced interferometer patterns, and a broad band of rather featureless emission concentrated to the plane of the Milky Way. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
39. Early days in radio and radar astronomy in Australia.
- Abstract
As in other countries, the first discoveries of Jansky and Reber in radio astronomy made little impression in Australia. Rather, interest in the subject was first aroused by news of the wartime discoveries of radio emission from the Sun by J. S. Hey in England and G. C. Southworth in the United States. As World War II wound down in 1945, the CSIR (later CSIRO) Radiophysics Laboratory in Sydney was ending its work on the development of radar equipment for the South West Pacific theatre of war. A wise decision was made to keep this highly experienced and imaginative group of people together and to look for new scientific and technical challenges. With the strong administrative encouragement of E, G. (Taffy) Bowen and the scientific foresight of J. L. Pawsey, the group turned its curiosity to radio astronomy, and in this way Australia got an early start in the opening up of this new branch of science (see the contribution by Bowen elsewhere in this volume). Those were exciting days and new discoveries came rapidly as existing equipment could be turned over to the exploration of the almost unknown radio sky. “COSMIC NOISE” Some experiments had been made in 1944 by Pawsey and Ruby Payne-Scott from the roof of the Radiophysics Laboratory building in the grounds of Sydney University, but the first significant observations were made by pointing antennas of Air Force and Army radar stations near Sydney at the Sun. The first years of solar work in Australia are described by W. N. Christiansen elsewhere in this volume. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
40. Optical and radio astronomers in the early years.
- Abstract
Radio noise from space was detected by Karl Jansky in 1931, working at the Bell Telephone Laboratories (Jansky 1933), This revolutionary discovery broke the barrier confining astronomical knowledge to the information contained, and the relevant physics, within the narrow band of wavelengths accessible (an octave and a half), and to positions and motions under purely gravitational forces. Jansky's wavelength was ten million times longer than that of light. His signals were radiated from the galactic center, 10,000 parsecs distant. The long wavelengths he used resulted in low angular resolution. There was no radial velocity information, no sharp spectral features (the first line was found twenty years later). For such reasons, and perhaps because he was an electrical engineer, no astronomer beat a pathway to his door; in fact I have never met any astronomer who personally knew him. Public recognition came only as an article in the New York Times (May 5, 1933) and a radio interview. His relevant bibliography includes only seven entries over the years 1932 to 1939, and he died young (see the article by Sullivan in this volume for further information on Jansky). As a summer resident of New Jersey seashore resorts in the early 1930s, I wore golf knickers, possibly even a hip flask, and drove an open car with a rumble seat (oh nostalgia!) past the giant antennas of the transatlantic radio transmitters for which Jansky's studies of noise background were to find the best operating wavelengths. Although I felt no premonitory twinges, I met my wife there, soon became interested in Jansky's results, and my life became linked with that place and time. [ABSTRACT FROM AUTHOR]
- Published
- 1984
- Full Text
- View/download PDF
41. Multiwavelength study of Cygnus A – III. Evidence for relic lobe plasma.
- Author
-
Steenbrugge, Katrien C., Heywood, Ian, and Blundell, Katherine M.
- Subjects
- *
CYGNUS A , *BINARY stars , *GALACTIC X-ray sources , *SPECTRUM analysis , *RADIO astronomy - Abstract
We study the particle energy distribution in the cocoon surrounding Cygnus A, using radio images between 151 MHz and 15 GHz and a 200 ks Chandra Advanced CCD Imaging Spectrometer-Imaging (ACIS-I) image. We show that the excess low-frequency emission in the lobe further from the Earth cannot be explained by absorption or excess adiabatic expansion of the lobe or a combination of both. We show that this excess emission is consistent with emission from a relic counterlobe and a relic counterjet that are being re-energized by compression from the current lobe. We detect hints of a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We do not detect relic emission in the lobe nearer to the Earth as expected from light traveltime effects assuming intrinsic symmetry. We determine that the duration of the previous jet activity phase was slightly less than that of the current jet-active phase. Further, we explain some features observed at 5 and 15 GHz as due to the presence of a relic jet. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
42. Interstellar Highly Ionized Species toward Cygnus: A Closer Look
- Author
-
Kevin S. Leach and Frederick Bruhweiler
- Subjects
Physics ,Stars ,H II region ,Ultraviolet astronomy ,Ionization ,Hubble space telescope ,medicine ,General Medicine ,Astrophysics ,Cygnus A ,medicine.disease_cause ,Ultraviolet ,Auger - Abstract
We examine Hubble Space Telescope (HST)/STIS data, complemented with International Ultraviolet Explorer (IUE) data, to delineate interstellar absorption of highly ionized species, C iv, Si iv, and N v, and low ionization species toward four stars in Cygnus. Previous IUE studies indicate two major velocity complexes for C iv and Si iv extending across Cygnus. We see interstellar N v in HST/STIS data for HD 190918 and Cyg X-1. In both stars, the N v is at the velocities of interstellar C iv and Si iv. In HD 190918, the N v is weak, possibly due to enhanced X-ray ionization produced by this binary system. The Cyg X-1 data are of low signal-to-noise, but N v is quite strong with a small b-value, indicating N v arises in a cooler H ii region resulting from X-ray Auger ionization by Cyg X-1.
- Published
- 2021
43. Constraints on the Mass Accretion Rate onto the Supermassive Black Hole of Cygnus A Using the Submillimeter Array
- Author
-
Geoffrey C. Bower, Kazunori Akiyama, Makoto Inoue, Patrick M. Koch, Shoko Koyama, Juan-Carlos Algaba, Wen Ping Lo, Jun Yi Koay, Hung Yi Pu, Satoki Matsushita, Paul T. P. Ho, Masanori Nakamura, Chihyin Tseng, Ramprasad Rao, and Keiichi Asada
- Subjects
Physics ,Supermassive black hole ,Active galactic nucleus ,Space and Planetary Science ,Radio galaxy ,Polarimetry ,Astronomy ,Astronomy and Astrophysics ,Cygnus A ,Submillimeter Array ,Submillimetre astronomy ,Radio astronomy - Abstract
We present the first detailed polarimetric studies of Cygnus A at 230 GHz with the Submillimeter Array (SMA) to constrain the mass accretion rate onto its supermassive black hole. We detected the polarized emission associated with the core at a fractional polarization of . This low fractional polarization suggests that the polarized emission is highly depolarized. One of the possible explanations is due to a significant variance in the Faraday rotation measure within the synthesized beam. By assuming the Faraday depolarization caused by inhomogeneous column density of the magnetized plasma associated with the surrounding radiatively-inefficient accretion flow within the SMA beam, we derived the constraint on the mass accretion rate to be larger than 0.15 yr−1 at the Bondi radius. The derived constraint indicates that an adiabatic inflow–outflow solution or an advection-dominated accretion flow should be preferable as the accretion flow model in order to explain the jet power of Cygnus A.
- Published
- 2021
44. DETECTION OF A RELIC X-RAY JET IN CYGNUS A.
- Author
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STEENBRUGGE, K. C., BLUNDELL, K. M., and DUFFY, P.
- Subjects
- *
CYGNUS A , *X-ray astronomy , *ASTROPHYSICAL jets , *COMPTON electrons , *COSMIC background radiation , *ELECTRON-nucleus scattering - Abstract
We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long linear feature seen in its counterlobe. This feature has a nonthermal spectrum and lies on the line connecting the brighter hotspot on the approaching side and the nucleus. We therefore conclude that this feature is (or was) a jet. However, the outer part of this X-ray jet does not trace the current counterjet observed in radio. No X-ray counterpart is observed on the jet side. Using light-travel time effects we conclude that this X-ray 50 kpc linear feature is a relic jet that contains enough low-energy plasma (γ ~ 103) to inverse-Compton scatter cosmic microwave background photons, producing emission in the X-rays. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
45. Multiwavelength study of Cygnus A – I. Precession and slow jet speeds from radio observations.
- Author
-
Steenbrugge, Katrien C. and Blundell, Katherine M.
- Subjects
- *
RADIO sources (Astronomy) , *CYGNUS A , *RADIO galaxies , *WAVELENGTHS , *JET planes - Abstract
We study the jet and counterjet of the powerful classical double Fanaroff–Riley type II (FR II) radio galaxy Cygnus A as seen in the 5-, 8- and 15-GHz radio bands using the highest spatial resolution and signal-to-noise ratio archival data available. We demonstrate that the trace of the radio knots that delineate the jet and counterjet deviates from a straight line and that the inner parts can be satisfactorily fitted with the precession model of Hjellming & Johnston. The parameter values of the precession model fits are all plausible although the jet speed is rather low (≲ 0.5 c) but, on investigation, found to be consistent with a number of other independent estimates of the jet speed in Cygnus A. We compare the masses and precession periods for sources with known precession and find that for the small number of active galactic nuclei with precessing jets the precession periods are significantly longer than those of microquasars. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
46. Multiwavelength study of Cygnus A – II. X-ray inverse-Compton emission from a relic counterjet and implications for jet duty cycles.
- Author
-
Steenbrugge, Katrien C., Blundell, Katherine M., and Duffy, Peter
- Subjects
- *
WAVELENGTHS , *CYGNUS A , *MAGNETIC fields , *COSMIC magnetic fields , *RADIO galaxies - Abstract
The duty cycles of powerful radio galaxies and quasars such as the prototype Cygnus A are poorly understood. X-ray observations of inverse-Compton-scattered cosmic microwave background (ICCMB) photons probe lower Lorentz-factor particles than radio observations of synchrotron emission, and thus potentially reveal a more aged population. Comparative studies of the nearer and farther lobes, separated by many tens of kiloparsecs and thus by tens of thousands of years in light-travel time, yield additional temporal resolution in studies of the life-cycles of such objects. We have co-added all archival Chandra ACIS-I data and present a deep 200-ks image of Cygnus A. This deep image reveals the presence of X-ray emission from a counterjet, i.e. a jet receding from Earth. The outer part of this counterjet does not overlie the current counterjet detected in radio emission, excluding the possibility that we are detecting the current counterjet in X-rays. This non-thermal X-ray emission has a power-law photon index of 1.7, and we interpret this emission as ICCMB radiation. There is an absence of any discernible X-ray emission associated with a jet flowing towards Earth. We make the following conclusions. (1) This emission is from a relic jet, indicating a previous episode of jet activity that took place prior to the current jet activity appearing as synchrotron radio emission. (2) The presence of X-ray emission from a relic counterjet of Cygnus A and the absence of X-ray emission associated with any relic approaching jet constrain the time-scale between successive episodes of jet activity to ∼106 yr. (3) Transverse expansion of the jet causes expansion losses, which shift the energy distribution to lower energies. Particles with initially high Lorentz factors, which originally gave detectable synchrotron radiation, attain Lorentz factors ∼103 and scatter CMB photons, to give X-ray emission. (4) Assuming that the electrons cooled as a result of adiabatic expansion, the required magnetic field strength is substantially smaller than the equipartition magnetic field strength. (5) A high minimum Lorentz factor for the distribution of relativistic particles in the current jet, of a few 103, seems to emerge from the central nucleus of this active galaxy. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
47. Radio and X-ray study of Cygnus A*.
- Author
-
Steenbrugge, Katrien C. and Blundell, Katherine M.
- Subjects
- *
RADIO galaxies , *RADIO sources (Astronomy) , *CYGNUS A , *GALACTIC X-ray sources , *ASTROPHYSICS - Abstract
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet “threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
48. Radio and X-ray study of Cygnus A*.
- Author
-
Steenbrugge, Katrien C. and Blundell, Katherine M.
- Subjects
RADIO galaxies ,RADIO sources (Astronomy) ,CYGNUS A ,GALACTIC X-ray sources ,ASTROPHYSICS - Abstract
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet “threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
49. Radio and X-ray study of Cygnus A.
- Author
-
Steenbrugge, Katrien and Blundell, Katherine
- Subjects
- *
ACTIVE galaxies , *JETS (Nuclear physics) , *X-rays , *RADIO sources (Astronomy) , *CYGNUS A , *RADIO astronomy - Abstract
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet “threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
50. Evolution of the radio emission of the Crab nebula from long-term observations at 927 and 151.5 MHz.
- Author
-
Vinyaikin, E.N.
- Subjects
- *
SOLAR radio emission , *NEBULAE , *CRAB Nebula , *CYGNUS A , *M87 (Galaxy) - Abstract
Radio flux measurements of the Crab nebula have been performed over many years relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. The inferred average secular rates of decrease in the radio flux of the Crab nebula are d 927 MHz = −0.18 ± 0.10% yr−1 over 1977–2000 and d 151.5 MHz = −0.3 ± 0.1% yr−1 over 1980–2003. The weighted mean flux-decrease rate averaged over several years of relative measurements at 86, 151.5, 927, and 8000 MHz is d mw = −0.17 ± 0.02% yr−1. The secular flux decrease is frequency independent, with an upper limit of | dα/ dt| < 3 × 10−4 yr−1 for the absolute value of the rate of change of the spectral index, and remains constant in time when averaged over long time intervals. The results of our measurements at 151.5 and 927 MHz combined with published absolute measurements at 81.5 and 8250 MHz are used to determine the radio spectrum of the Crab nebula for epoch 2010.0. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
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