Publications on the WWW

Kinematics of kiloparsec-scale Jets
  • by R.A.Laing and A.H.Bridle
  • Proc. I.A.U. Symp. No. 313, 'Extragalactic Jets from Every Angle', eds. F.Massaro, C.C.Cheung, E.Lopez and A.Siemiginowska, Cambridge Univ. Press (2015), 108-115.
  • It has long been known that kiloparsec-scale jets in radio galaxies can be divided into two flavours: strong (found in powerful sources, narrow and terminating in compact hot-spots) and weak (found in low-luminosity sources, flaring, unable to form hot-spots and terminating in diffuse lobes or tails). Both flavours are initially relativistic, but weak jets decelerate to sub-relativistic, transonic speeds by entraining external gas while strong jets remain relativistic and supersonic until they terminate. Much is now known about the kinematics of weak-flavour jets, which can be modelled as intrinsically symmetrical, decelerating relativistic flows, and we summarize the results of our work in this area. Strong-flavour jets are relatively faint and narrow, so it has hitherto proved difficult to obtain the necessary deep, transverse-resolved images in total intensity and linear polarization. The spectacular jets in the radio galaxy NGC6251 appear to represent a transition case between weak and strong flavours: the jets show no clear evidence for deceleration, but are relatively wide. VLA observations hint at transverse velocity structure with a very fast (Lorentz factor >5) spine surrounded by a slower shear layer. New observations with the upgraded VLA should be able to test this picture.
Systematic Properties of Decelerating Relativistic Jets in Low-luminosity Radio Galaxies
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 437, 3405-3441 (2014)
  • We model the kiloparsec-scale synchrotron emission from jets in ten Fanaroff-Riley Class I radio galaxies for which we have sensitive, high-resolution imaging and polarimetry from the Very Large Array. We assume that the jets are intrinsically symmetrical, axisymmetric, decelerating, relativistic outflows and we infer their inclination angles and the spatial variations of their flow velocities, magnetic field structures and emissivities using a common set of fitting functions. The inferred inclinations agree well with independent indicators. The spreading rates increase rapidly, then decrease, in a flaring region. The jets then recollimate to form conical outer regions at distance r0 from the active galactic nucleus (AGN). The flaring regions are homologous when scaled by r0. At ~0.1r0, the jets brighten abruptly at the onset of a high-emissivity region and we find an outflow speed of ~0.8c, with a uniform transverse profile. Jet deceleration first becomes detectable at ~0.2r0 and the outflow often becomes slower at its edges than it is on-axis. Deceleration continues until ~0.6r0, after which the outflow speed is usually constant. The dominant magnetic-field component is longitudinal close to the AGN and toroidal after recollimation, but the field evolution is initially much slower than predicted by flux-freezing. In the flaring region, acceleration of ultrarelativistic particles is required to counterbalance the effects of adiabatic losses and account for observed X-ray synchrotron emission, but the brightness evolution of the outer jets is consistent with adiabatic losses alone. We interpret our results as effects of the interaction between the jets and their surroundings.
The Spectra of Jet Bases in FR I Radio Galaxies: Implications for Particle Acceleration
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 432, 1114-1132 (2013)
  • Accurate, spatially-resolved VLA imaging of the bases of the radio jets and counter-jets in eleven Fanaroff-Riley Class I (FR I) radio galaxies shows that the spectral index initially decreases away from the AGN in all of the jets.
  • The mean spectral indices are 0.66 +/- 0.01 where the jets first brighten abruptly and 0.59 +/- 0.01 after they recollimate.
  • Our decelerating relativistic jet models associate the decrease in spectral index with a bulk deceleration of the flow from 0.8c to <0.5c.
  • We suggest that the decrease in spectral index is the result of a change in the characteristics of ongoing particle acceleration.
  • A possible mechanism is the first-order Fermi process in mildly relativistic shocks in the Bohm limit.
Relativistic Jet Models for two Low-luminosity Radio Galaxies: Evidence for Backflow?
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 424, 1149-1169 (2012)
  • Sensitive, well-resolved VLA imaging of the radio jets and counter-jets in two lobed Fanaroff-Riley Class I (FR I) radio galaxies - B2 0206+35 (UGC 1651) and B2 0755+37 (NGC 2484) - shows both jets in both sources have two-component structure transverse to their axes.
  • Close to the jet axis, a centrally-darkened counter-jet lies opposite a centrally-brightened jet, while both are surrounded by broader collimated emission that is brighter on the counter-jet side.
  • Asymmetries in total intensity and linear polarization between jets and counter-jets can be accounted for if the jets are intrinsically symmetrical, with decelerating relativistic outflows similar to those in plumed FR I sources surrounded by mildly relativistic backflows containing predominantly toroidal magnetic fields.
  • Backflows return to within a few kpc of the galaxies at roughly 0.25c and radiate with a synchrotron spectral index near 0.55.
  • We discuss whether backflow should be expected in lobed FR I sources and suggest further observations to test the backflow hypothesis.
The Magnetized Medium Around the Radio Galaxy B2 0755+75: An Interaction with the Intra-Group Gas
  • by D.Guidetti, R.A.Laing, J.H.Croston, A.H.Bridle, and P.Parma
  • Monthy Notices of the Royal Astronomical Society, 423, 1335-1350 (2012)
  • Detailed VLA imaging of Faraday rotation (RM) and depolarization over isolated radio galaxy B2 0755+37.
  • New X-ray data from XMM-Newton.
  • Complex RM distribution with evidence for anisotropic fluctuations in two regions.
  • RM power spectra well described by cut-off power laws with slopes ranging from 2.1 to 3.2 in different sub-regions; magnetic-field autocorrelation lengths from 0.25 to 1.4 kpc.
  • Variation of RM fluctuation amplitude source inconsistent with expectation from beta-model gas distribution fitted to X-ray data, even allowing for cavities in thermal gas associated with radio lobes.
  • Fluctuations likely produced by compressed gas and field around leading edges of lobes.
  • High depolarization around jets and inner lobes could be produced by dense gas surrounding source containing magnetic field which is tangled on small scales.
  • We identify four ways in which the depolarization (Faraday depth) asymmetry between jetted and counter-jetted lobes of extended radio sources can be modified by interactions with the surrounding medium.
Observational Details: Radio
  • by A.H.Bridle and M.H.Cohen
  • Chapter 5 of "Relativistic Jets from Active Galactic Nuclei", eds. Markus B÷ttcher, Daniel E. Harris, and Henric Krawczynski, p.117-152 (Wiley 2012)
  • Reviews the observed radio properties of relativistic jets from AGN on parsec to many-kiloparsec scales, with application to deriving jet kinematics from the radio data.

New Technologies for Radio Astronomy
  • by K.Y.Lo and A.H.Bridle
  • in The Astronomy Revolution: 400 Years of Exploring the Cosmos, eds. Donald G.York, Owen Gingerich, and Shuang-Nan Zhang, Taylor and Francis (2011)
  • From an international conference celebrating new visions in astronomy 400 years after the invention of the optical telescope.
  • How new radio astronomical techniques have led to important discoveries in astronomy.
  • How further technical developments are leading to new facilities such ALMA and the SKA Program.

Deep Imaging of Fanaroff-Riley Class I Radio Galaxies with Lobes
  • by R.A.Laing, D.Guidetti, A.H.Bridle, P.Parma, and M.Bondi
  • Monthy Notices of the Royal Astronomical Society, 417, 2789-2808 (2011)
  • We present deep, high-resolution imaging of the nearby Fanaroff-Riley Class I FR I radio galaxies NGC 193, B2 0206+35, B2 0755+37 and M 84 at frequencies of 4.9 and 1.4 GHz using new and archival multi-configuration observations from the Very Large Array. In addition, we describe lower-resolution observations of B2 0326+39 and a reanalysis of our published images of 3C 296. All of these radio galaxies show twin jets and well-defined lobes or bridges of emission, and we examine the common properties of this class of source. We show detailed images of total intensity, brightness gradient, spectral index, degree of polarization and projected magnetic-field direction. The jet bases are very similar to those in tailed twin-jet sources and show the characteristics of decelerating, relativistic flows. Except on one side of M 84, we find that the jets can be traced at least as far as the ends of the lobes, where they often form structures which we call "caps'' with sharp outer brightness gradients. Continuing, but less well collimated flows back into the lobes from the caps can often be identified by their relatively flat spectral indices. The lobes in these radio galaxies are similar in morphology, spectral-index distribution and magnetic-field structure to those in more powerful (FR II) sources, but lack hot-spots or other evidence for shocks at the ends of the jets. M 84 may be an intermediate case between lobed and tailed sources, in which one jet does not reach the end of its lobe, but disrupts to form a "bubble''.

Ordered Magnetic Fields Around Radio Galaxies: Evidence for Interaction with the Environment
  • by D.Guidetti, R.A.Laing, A.H.Bridle, P.Parma, and L.Gregorini
  • Monthy Notices of the Royal Astronomical Society, 413, 2525-2544 (2011)
  • We present detailed imaging of Faraday rotation and depolarization for the radio galaxies 0206+35, 3C 270, 3C 353 and M 84, based on Very Large Array observations at multiple frequencies in the range 1365 to 8440 MHz. This work suggests a more complex picture of the magneto-ionic environments of radio galaxies than was apparent from earlier work. All of the sources show spectacular banded rotation measure (RM) structures with contours of constant RM perpendicular to the major axes of their radio lobes. We give a comprehensive description of the banded RM phenomenon and present an initial attempt to interpret it as a consequence of interactions between the sources and their surroundings. We show that the material responsible for the Faraday rotation is in front of the radio emission and that the bands are likely to be caused by magnetized plasma which has been compressed by the expanding radio lobes. A two-dimensional magnetic structure in which the field lines are a family of ellipses draped around the leading edge of the lobe can produce RM bands in the correct orientation for any source orientation. We also report the first detections of rims of high depolarization at the edges of the inner radio lobes of M 84 and 3C 270. These are spatially coincident with shells of enhanced X-ray surface brightness, in which both the field strength and the thermal gas density are likely to be increased by compression.

Structures of the Magnetoionic Media Around the Fanaroff-Riley Class I Radio Galaxies 3C 31 and Hydra A
  • by R.A.Laing, A.H.Bridle, P.Parma, and M.Murgia
  • Monthy Notices of the Royal Astronomical Society, 391, 521-549 (2008)
  • We use high-quality VLA images of the Fanaroff & Riley Class I radio galaxy 3C 31 at six frequencies in the range 1365 to 8440 MHz to explore the spatial scale and origin of the rotation measure (RM) fluctuations on the line of sight to the radio source. We analyse the distribution of the degree of polarization to show that the large depolarization asymmetry between the North and South sides of the source seen in earlier work largely disappears as the resolution is increased. We show that the depolarization seen at low resolution results primarily from unresolved gradients in a Faraday screen in front of the synchrotron-emitting plasma. We establish that the residual degree of polarization in the short-wavelength limit should follow a Burn law and we fit such a law to our data to estimate the residual depolarization at high resolution. We show that the observed RM variations over selected areas of 3C 31 are consistent with a power spectrum of magnetic fluctuations in front of 3C 31 whose power-law slope changes significantly on the scales sampled by our data. The power spectrum can only have the form expected for Kolmogorov turbulence on scales <5 kpc. On larger scales we find a flatter slope. We also compare the global variations of RM across 3C 31 with the results of three-dimensional simulations of the magnetic-field fluctuations in the surrounding magnetoionic medium. We show that our data are consistent with a field distribution that favours the plane perpendicular to the jet axis - probably because the radio source has evacuated a large cavity in the surrounding medium. We also apply our analysis techniques to the case of Hydra A, where the shape and the size of the cavities produced by the source in the surrounding medium are known from X-ray data.

Frontiers of Astrophysics: A Celebration of NRAO's 50th Anniversary
  • edited by Alan H. Bridle, James J. Condon, and Gareth C. Hunt
  • Astronomical Society of the Pacific Conference Series, Vol. 395 (2008)
  • In celebration of its 50th anniversary, the NRAO hosted a science symposium highlighting the most important questions that can be addressed by astronomers: the creation of the universe, the formation of the first stars and galaxies, to the production of the elements, the assembly of molecules and the building blocks of life in interstellar space, how and where planets form, and possible changes in fundamental physical constants on cosmological time scales. This symposium brought together leading scientists to address the most important questions in these areas, the major contributions to astronomy enabled by NRAO instruments -- past, present, and future -- and to suggest future directions for research involving radio observations and techniques.
Table of Contents

Multifrequency VLA Observations of the FR I Radio Galaxy 3C 31: Morphology, Spectrum and Magnetic Field
  • by R.A.Laing, A.H.Bridle, P.Parma, L.Feretti, G.Giovannini, M.Murgia, and R.A.Perley
  • Monthly Notices of the Royal Astronomical Society, 386, 657-672 (2008)
  • Spectral and magnetic structure within the jets of 3C 31
  • Brightest X-ray emission not associated with flattest radio spectra, but with particle acceleration mechanism of characteristic energy index 2.24. Flattest radio spectra associated with jet deceleration and regions of transverse velocity shear.
  • Magnetic field aligned with emission arcs whose properties differ between jet and counterjet, consistent with differential relativistic aberration.

Magnetic-Field Fluctuations Around the Radio Galaxy 3C 31
  • by R.A.Laing and A.H.Bridle
  • in "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray", eds. T.A.Rector and D.S.De Young, ASP Conference Series, 386, 104-109 (2008)
  • Analysis of the magnetic-field fluctuations in front of the radio galaxy 3C31.
  • Fluctuations must be due primarily to foreground medium.
  • Determine RM structure function and compare with 3-d simulations of RM produced by tangled field in plasma surrounding 3C31.
  • Consistent with spherical plasma distribution in which radio source has produced a cavity.

Jet Spectra in FR I Radio Galaxies: Implications for Particle Acceleration
  • by R.A.Laing, A.H.Bridle, W.D.Cotton, D.M.Worrall, and M.Birkinshaw
  • in "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray", eds. T.A.Rector and D.S.De Young, ASP Conference Series, 386, 100-114 (2008)
  • Accurate imaging of radio spectral index for the inner jets in three FR I radio galaxies.
  • Where jets first brighten, small dispersion around spectral index of 0.62 in region where bright X-ray emission is detected.
  • Further from nucleus, spectral index flattens to 0.50 - 0.55 and X-ray emission fainter relative to radio.
  • Brightest X-ray emission not associated with flattest radio spectra, but with particle-acceleration process whose characteristic energy index is 2.24.
  • Change in spectral index occurs roughly where relativistic jet models require rapid deceleration.

Jet-environment Interactions in FR I Radio Galaxies
  • by R.A.Laing and A.H.Bridle
  • in "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray", eds. T.A.Rector and D.S.De Young, ASP Conference Series, 386, 70-79 (2008)
  • Unequivocal evidence that the jets in FR I radio galaxies are initially relativistic, decelerating flows
  • Mass entrainment -from stellar mass loss within the jet volume or via a boundary layer at the jet surface is the most likely cause for deceleration.
  • Consistent with velocity field and geometry inferred from kinematic modelling and external gas density and pressure profiles derived from X-ray data. .
  • Jets must initially be very light, perhaps with an electron-positron composition.

The Inner Jet of Radio Galaxy NGC 315 as Observed with Chandra and the VLA
  • by D.M.Worrall, M.Birkinshaw, R.A.Laing, W.D.Cotton, and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 380, 2-14 (2007)
  • Deep imaging of the jet, nucleus and gaseous atmosphere of NGC315 with the Chandra X-ray observatory are compared with high-resolution VLA imaging at 5 GHz.
  • Diffuse X-ray synchrotron emission is detected from the jet through regions both of fast bulk flow and deceleration. diffuse emission.
  • The X-ray to radio ratio provides evidence for distributed particle acceleration throughout the fast moving region. .
  • A remarkable knotty filament within the jet is seen in both the radio and the X-ray; its oscillatory apearance, roughly aligned magnetic field and requirements for particle acceleration suggest that it is a magnetic strand within a shear layer between fast inner and slower outer flow.
PDF (0.9 Mb)

Radio Jets as Decelerating Relativistic Flows
  • by R.A.Laing, A.H.Bridle, and J.R.Canvin
  • in "Relativistic Astrophysics and Cosmology: Einstein's Legacy", eds. B. Aschenbach, V. Burwitz, G. Hasinger, and B. Leibundgut, Springer-Verlag, 445-448 (2007)
  • The largest-scale manifestation of Special Relativistic aberration in contemporary astrophysics is the appearance of initial asymmetries in kpc-scale radio-galaxy jets. We discuss how the Doppler beaming and Special Relativistic aberration modify the sidedness and polarization properties of intrinsically symmetrical relativistic flows and how these effects can be used to estimate the physical parameters of the jets in low-luminosity extragalactic radio sources.
PDF (0.24 Mb)

A Relativistic Model of the Radio Jets in 3C 296
  • by R.A.Laing, J.R.Canvin, A.H.Bridle, and M.J.Hardcastle
  • Monthly Notices of the Royal Astronomical Society, 372, 510-536 (2006)
  • Deep imaging with the VLA is used to determine the distributions of spectral index, Faraday rotation measure, and apparent magnetic field over this nearby, low-luminosity radio galaxy.
  • The flatter-spectrum radio jets are surrounded by a sheath of steeper-spectrum diffuse emission.
  • We apply an intrinsically-symmetrical decelerating relativistic jet model to determine the velocity field of the jets. On-axis, they decelerate from v/c ∼ 0.8 to v/c ∼ 0.4 around 5 kpc from the nucleus with lower velocities everywhere at their edges.
  • Our observations rule out a globally-ordered, helical magnetic field configuration but are well modeled by a field that is random on small scales but anisotropic, with toroidal and longitudinal components only.
  • We interpret systematic morphological differences between local brightness enhancements ("arcs") in the main and counter-jets as a new effect of relativistic aberration.
PDF (1.7 Mb)

Magnetic Fields in Jets: Ordered or Disordered?
  • by R.A.Laing, J.R.Canvin, and A.H.Bridle
  • in "The Origin and Evolution of Cosmic Magnetism", eds. R.Beck, G.Brunetti, L.Feretti, and B.Gaensler, Astronomisches Nachtrichten. 327, 523- 526 (2006)
  • Large-scale helical fields are incompatible with our VLA polarimetry of the jets in FRI radio galaxies
  • The combination of an ordered toroidal and disordered poloidal component is consistent with our data, as is a fully disordered, (but anisotropic) field.
  • Jets must also contain small but significant amounts of radial field.
PDF (0.36 Mb)

Faraday Rotation Variations Along Radio Jets: the Magnetic Field in Galaxy and Group Halos
  • by R.A.Laing, J.R.Canvin, W.D.Cotton, A.H.Bridle, and P.Parma
  • in "The Origin and Evolution of Cosmic Magnetism", eds. R.Beck, G.Brunetti, L.Feretti, and B.Gaensler, Astronomisches Nachtrichten, 327, 533-534 (2006)
  • The fluctuations of the rotation measure are larger in the fainter (receding) jets of two well-resolved FRI radio galaxies, as expected if the rotation occurs in the hot galaxy/group halos and the jet asymmetry is due to relativistic beaming.
PDF (0.36 Mb)
Multifrequency Observations of the Jets in the Radio Galaxy NGC 315
  • by R.A.Laing, J.R.Canvin, W.D.Cotton, and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 368, 48-64 (2006).
  • Five-frequency imaging with the VLA is used to determine the distributions of spectral index and Faraday rotation measure over the inner ± 400 arcsec of this giant low-luminosity radio galaxy
  • The spectral structure suggests a change of dominant particle acceleration mechanism with distance from the nucleus. A transverse gradient from 0.55 on axis to 0.44 at the edge of the jet may be associated with a shear in the jet velocity field.
  • The distribution of the Faraday rotation has three components. A constant term and a linear gradient are probably due to our Galaxy. Residual fluctuations are smaller in the brighter (approaching) jet, consistent with the idea that they are produced by magnetic fields in a halo of hot plasma that
  • We also image the apparent magnetic field structure of the jets over the first ± 200 arsec from the nucleus.
full-resolution PDF (11 Mb)

A Relativistic Model of the Radio Jets in NGC 315
  • by J.R.Canvin, R.A.Laing, A.H.Bridle, and W.D.Cotton
  • Monthly Notices of the Royal Astronomical Society, 363, 1223-1240 (2005).
  • Applies an intrinsically symmetrical decelerating relativistic jet model to deep VLA imaging of the flaring region of the jets in the giant low-luminosity radio galaxy NGC 315.
  • The inferred velocity, emissivity and field structure are very similar to those of other low-luminosity sources but all of the physical scales are larger by a factor of about 5.
  • Simple adiabatic models fail to fit the emissivity variations.
PDF (1.2 Mb)

A Chandra Observation of the X-ray Environment and Jet of 3C296
  • by M.J.Hardcastle, D.M.Worrall, M.Birkinshaw, R.A.Laing, and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 358, 843-850 (2005).
  • Observations of the twin-jet radio galaxy 3C296 with Chandra detect X-ray emission from the nucleus, from the inner parts of the radio jet, and from a small-scale thermal environment around the jet deceleration region.
  • The X-ray jet and a steep pressure gradient in the external thermal environment are associated with the region where strong bulk deceleration of the jet material is suggested by radio observations.
PDF (545 kb)

Observations of Jet Dissipation
  • by R.A.Laing, J.R.Canvin, and A.H.Bridle
  • "X-ray and Radio Connections", eds. Sjouwerman, L.O. and Dyer, K.K. (2004)
  • Summarizes a project to determine physical conditions in the jets of low-luminosity (FR I) radio galaxies by modeling them as intrinsically symmetrical, relativistic, decelerating flows.
  • Derives the three-dimensional distributions of velocity, rest-frame emissivity and magnetic-field structure in the jets. Outlines implications for theories of jet deceleration, including the use of conservation-law analysis to obtain profiles of internal pressure, density, Mach number and entrainment rate along the jets
PDF (712 kb)

Adiabatic Relativistic Models for the Jets in the Radio Galaxy 3C31
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 348, 1459-1472 (2004)
  • General approach to modeling brightness and polarization structure of adiabatic, decelerating, relativistic jet
  • Adiabatic models provide progressively better descriptions of 3C31 jets at larger distances from the galactic nucleus
  • Evidence that particles are preferentially injected where bright X-ray emission found
Abstract as HTML
PDF (1.1 Mb)

X-ray Detection of the Inner Jet in the Radio Galaxy M84
  • by D.E.Harris, A. Finoguenov, A.H.Bridle, M.J.Hardcastle, and R.A.Laing
  • Astrophysical Journal, 580, 110-113 (2002)
  • Chandra data show X-ray emission aligned with the northern radio jet
  • Synchrotron emission is the favored explanation for the observed X-rays
Abstract as HTML
PDF (140 kb)

Dynamical Models for Jet Deceleration in the Radio Galaxy 3C31
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 336, 1161-1180 (2002)
  • Applies relativistic conservation laws to determine the energy, momentum and mass fluxes in the decelerating jets in an FRI radio galaxy
  • Evidence that entrainment from galactic atmosphere is dominant mass input process far from galactic nucleus
  • Stellar mass loss may also contribute to deceleration near flaring point of jet
  • Compatible with initial electron-positron jet picking up thermal matter from stellar mass loss, or electron-proton jet with low-energy cutoff
Abstract as HTML
PDF (1 Mb)

A Chandra Observation of the X-ray Environment and Jet of 3C31
  • by M.J.Hardcastle, D.M.Worrall, M.Birkinshaw, R.A.Laing, and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 334, 182-192 (2002)
  • Deep Chandra imaging of the X-ray jet and hot gas in and around 3C31
  • Derives density, temperature and pressure distribution in atmosphere of host galaxy
  • Provides constraints on physical properties and stability of jets
Abstract as HTML
PDF (443 kb)

Relativistic Models and the Jet Velocity Field in the Radio Galaxy 3C31
  • by R.A.Laing and A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 336, 328-352 (2002)
  • Deep VLA imaging of the jets in 3C31 fitted by models of symmetric, antiparallel, axisymmetric, time-stationary relativistic flows
  • Derives jet orientation, velocity field, emissivity variation and magnetic field configuration
  • Evidence that jets decelerate by entraining the external medium
  • Predicts appearance of jet at range of angles to line of sight, with implications for unified models
Abstract as HTML
Animations showing the jets at different angles to the line of sight
PDF (2.2 Mb)

Jet reorientation in AGN: Two Winged Radio Galaxies
Abstract as HTML
compressed Postscript (383 kb)

Multiwavelength Observations of the Second Largest Known FRII Radio Galaxy, NVSS 2146+82
  • by Christopher Palma, Franz Bauer, William Cotton, Alan Bridle, Steven Majewski, and Craig Sarazin
  • Astronomical Journal, 119, 2068-2084 (2000)
  • radio, optical and X-ray imaging and spectroscopy of a giant radio galaxy at z=0.145
  • second largest known FR II radio source, 4 Mpc across
  • discovered by the NRAO VLA Sky Survey
Abstract as HTML
PDF (1.5 Mb)

Asymmetry of Jets, Lobe Size and Spectral Index in Radio Galaxies and Quasars
Abstract as HTML
compressed PostScript (255 Kb)

Impact of the VLA: Physics of AGN Jets
  • by Alan Bridle
  • Barry Clark at 60, Socorro, June 1998
  • imaging NGC315 as an example of the VLA's impact on jet physics
compressed PostScript (889 Kb)

Internal Structure of the Jets in 3C353
  • by Mark Swain, Alan Bridle, and Stefi Baum
  • Astrophysical Journal, 507, L29-L33 (1998)
  • high-resolution VLA imaging of jet and counterjet in a nearby FR II radio galaxy
  • modeling of emissivity and magnetic field distributions within the jet
  • evidence that most of emission is from a thick boundary (shear) layer

compressed PostScript (168 Kb)
Color image (36k GIF)

Asymmetry of Jets, Lobe Length and Spectral Index in Quasars
  • by Jane Dennett-Thorpe, Alan Bridle, Peter Scheuer, Robert Laing, and Patrick Leahy
  • untangling intrinsic and apparent asymmetries in synchrotron emission from powerful double radio sources
  • Monthly Notices of the Royal Astronomical Society, 289, 753-765 (1997)
Abstract as HTML
compressed PostScript (310 Kb)

Energy Transport in Radio Galaxies and Quasars
  • a Workshop held Sept 19-23 1995 at the University of Alabama
  • proceedings in A.S.P. Conf. Series, Vol.100 (1996)
  • eds. Philip Hardee, Alan Bridle, Anton Zensus

The Jets in the Radio Galaxy 3C353
  • by Mark Swain, Alan Bridle, and Stefi Baum
  • contributed paper in A.S.P. Conf. Series, Vol. 100, pp. 299-304 (1996)
  • high-resolution VLA imaging of a nearby radio galaxy
  • highest linear resolution ever on a large-scale FR II jet
  • evidence for boundary (shear) layer and "sheath" emissions
compressed PostScript (119 Kb)
Color image (36k GIF)

Observations of Energy Transport
  • by Alan Bridle
  • review paper in A.S.P. Conf. Series, vol. 100, pp. 383-394 (1996)
  • discussion of jet velocities, velocity fields, and unification
  • highlights of observational results presented at the meeting
compressed PostScript (47 Kb)

Deep VLA Imaging of Twelve Extended 3CR Quasars
  • by Alan Bridle, David Hough, Colin Lonsdale, Jack Burns, and Robert Laing
  • Astronomical Journal, 108, 766-820 (1994)
  • sensitive high-resolution radio imaging and polarimetry
  • implications for physics of energy transport by jets
Abstract as HTML

Origin of the Structures and Polarization in the Classical Double 3C 219
  • by David A. Clarke, Alan H. Bridle, Jack O. Burns, Richard A. Perley and Michael L. Norman
  • Astrophysical Journal, 385, 173-187 (1992)
  • High dynamic range VLA images at four frequencies with 1.4-arcsec resolution
  • Extended filamentary emission of the lobes
  • A second type of filamentation, spatially independent of the total intensity filaments, in the depolarization is associated with strong local gradients in the rotation measure
  • Evidence for a clumpy magnetoionic medium around the radio galaxy
  • The strengths and weaknesses of two interpretations of the abbreviated jets are considered
PDF (5 Mb)

Sidedness, Field Configuration, and Collimation of Extragalactic Radio Jets
  • by A.H.Bridle
  • Astronomical Journal, 89, 979-986 (1984)
  • Data on 125 extragalactic jets show that those in lower-power sources are generally two-sided and dominated by perpendicular magnetic field components over most of their lengths while those in higher-power sources are one-sided and dominated by parallel magnetic field over most of their lengths.
  • The resolved jets in the weaker sources generally have faster lateral expansion (spreading) rates than those in the more powerful sources.
High-Resolution VLA Observations of the Radio Jet in NGC6251
  • by R.A.Perley, A.H.Bridle and A.G.Willis
  • Astrophysical Journal Supplement Series, 54, 291-334 (1984)
  • High dynamic range VLA images at four frequencies with 1.15 to 15-arcsec resolution
  • Collimation and brightness evolution of the jet
  • Magnetic field configuration and rotation measure distribution over the jet
  • Implications for physics of the jet
Flux Densities, Positions, and Structures for a Complete Sample of Intense Radio Sources at 1400 MHz
  • by A.H.Bridle, M.M.Davis, E.B.Fomalont and J.Lequeux
  • Astronomical Journal, 77, 405 - 443 (1972)
  • Accurate flux densities, precise positions of unresolved sources, and structures of resolved sources, for a 424 sources whose 1400-MHz integrated flux densities exceed 1.7 Jy.
  • The 234 sources with 1400-MHz flux densities above 2 Jy, equivalent diameters less than 10 arcmin, and galactic latitude above 20 deg form a 98+/-2 per cent complete sample comparable in number to the Third Cambridge Catalogue in this 4.3-steradian area of sky.
  • Later known as the "BDFL" source catalog.
Observations of Radio Sources at 10.03 MHz
  • by A.H.Bridle and C.R.Purton
  • Astronomical Journal, 73, 717-726 (1968)
  • Flux densities are derived for 124 radio sources which have been observed with the 10.03 MHz telescope at the Dominion Radio Astrophysical Observatory.
  • The procedure used to correct the observations for ionospheric effects, and the method of calibration of the flux density scale are described.
The Spectrum of the Radio Background Between 13 and 404 MHz
  • by A.H.Bridle
  • Monthly Notices of the Royal Astronomical Society, 136, 219-240 (1967)
  • Measurements of the brightness temperature of the radio background over a range of declinations at frequencies of 13.15, 17.5, and 81.5 MHz are described. Geometrically scaled aerials having beamwidths of 17 deg by 12 deg and 53 deg by 12 deg have been used, and the results are compared to deduce the spectrum of the background between these frequencies.
  • The observed variation of the spectral index across the sky is fitted by a model in which the galactic contribution has temperature spectral indices 2.38 +/- 0.03 and 2.46 +/- 0.04 for two different regions of sky, superposed upon an isotropic background due to to radio galaxies, amounting to 30 +/- 7 K at 178 MHz. The galactic contributions are considered to be associated with radiation from the local spiral arm and from the inter-arm, respectively.
  • The results are compared with those of other workers at 26.3, 38, 81.5, 178, and 404 MHz. The observed energy spectrum of primary cosmic ray electrons is shown to be consistent with that deduced from the new radio data.

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