An Atlas of Supernova Remnant Magnetic Fields

Milne, D. K.

doi:10.1071/ph870771

Cited by 68 publications

(60 citation statements)

References 6 publications

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“…Except in circumstances with preferential alignments between the motion and the field, that would lead to the further conclusion that even a weak magnetic field will have a substantial impact on the evolution and dynamics of supersonic clumps of ionized, conducting gas. In young supernova remnants, polarized radio synchrotron emission indicates that there is a net radial direction to the magnetic field inside the remnants (Milne 1987). This might suggest that bullets in young remnants would generally encounter a radial field and, hence, one nearly aligned with their motions.…”

Section: Discussionmentioning

confidence: 99%

The Magnetohydrodynamics of Supersonic Gas Clouds: MHD Cosmic Bullets and Wind‐swept Clumps

Jones

Ryu

Tregillis

1996

ApJ

157

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We report an extensive set of two-dimensional MHD simulations exploring the role and evolution of magnetic fields in the dynamics of supersonic plasma clumps. We examine the influence of both ambient field strength and orientation on the problem. Of those two characteristics, field orientation is far more important in the cases we have considered with β 0 = p g /p b ≥ 1. That is due to the geometry-sensitivity of field stretching/amplification from large-scale shearing motions around the bullet. When the ambient magnetic field is transverse to the bullet motion, even a very modest field, well below equipartition strength, can be amplified by field line stretching around the bullet within a couple of bullet crushing times so that Maxwell stresses become comparable to the ram pressure associated with the bullet motion. The possibility is discussed that those situations might lead to large, induced electric potentials capable of accelerating charged particles. When the ambient field is aligned to the bullet motion, on the other hand, reconnection-prone topologies develop that shorten the stretched field and release much of the excess energy it contains. In this geometry, the Maxwell stresses on the bullet never approach the ram pressure level. In both cases, however, the presence of a field with even moderate initial strength acts to help the flow realign itself around the bullet into a smoother, more laminar form. That reduces bullet fragmentation tendencies caused by destructive instabilities. Eddies seem less effective at field amplification than flows around the bullet, because fields within eddies tend to be expelled to the eddy perimeters. Similar effects cause the magnetic field within the bullet itself to be reduced below its initial value over time.For oblique fields, we expect that the transverse field cases modeled here are more generally relevant. What counts is whether field lines threading the face of the bullet are swept around it in a fashion that folds them (leading to reconnection) or

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Section: Discussionmentioning

confidence: 99%

The Magnetohydrodynamics of Supersonic Gas Clouds: MHD Cosmic Bullets and Wind‐swept Clumps

Jones

Ryu

Tregillis

1996

ApJ

157

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“…implying that the magnetic field is highly disordered on scales below 1 arcsec (Milne 1987). Another cause of reduced polarization at radio wavelengths is rotation due to the Faraday effect, in which the plane of polarization is rotated as the polarized waves pass through a magnetized plasma.…”

Section: Figurementioning

confidence: 99%

Cassiopeia A: dust factory revealed via submillimetre polarimetry

Dunne

Maddox

Ivison

et al. 2009

Monthly Notices of the Royal Astronomical Society

124

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If Type-II supernovae - the evolutionary end points of short-lived, massive stars - produce a significant quantity of dust (>0.1 M_sun) then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type-II supernovae. In this paper we present new data which show that the submm emission from Cas A is polarised at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarised submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarisation in this way and so we attribute the excess polarised submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarised and unpolarised dust emission in the north of the remnant, where there is no contamination from foreground molecular clouds. The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which, coupled with the brief timescale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where f_pol=2-7%), or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou

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“…This is somewhat surprising, both intuitively and based on that observed in several other spirals with radio lobes (Wilson & Ulvestad 1987;Duric & Seaquist 1988), however the sample of such objects is noticeably small (see Section 4.4). Although the fields observed around young supernova remnants (SNRs) are also tangential, the morphology seen in Circinus is more akin to that observed in older SNRs where radial fields are commonly observed (Milne 1987;Dickel, van Breugel & Strom 1991). Radial fields are thought to be caused by Rayleigh-Taylor (R-T) instabilities at the shock front (Gull 1973;1975).…”

Section: The Magnetic Field Geometrymentioning

confidence: 99%

Radio continuum evidence for nuclear outflow in the Circinus galaxy

Elmouttie

Haynes

Jones

et al. 1998

Monthly Notices of the Royal Astronomical Society

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Australia Telescope Compact Array radio continuum maps of the edge‐on galaxy in Circinus are presented for four frequencies. The unresolved core of the galaxy measures less than 20 pc in diameter and has a flat spectral index of α =−0.06 ± 0.15 (S ∝ να). An arcsecond‐scale jet close to the core is directed similarly to the previously detected larger scale plumes. The core is surrounded by what we believe to be a diffuse radio counterpart to the recently discovered r = 200 pc starburst ring. The large radio lobes are shown to consist of central plume features surrounded by edge‐brightened emission. The polarized emission from these lobes is mainly contained within these distinct plume and edge‐brightened features, the latter showing very high degrees of polarization (> 50 per cent at λ= 6 cm). A study of the depolarization and rotation measures indicates that with respect to the galactic disc, the northern radio lobe is in the foreground and directed towards us whilst the opposite is true for the southern lobe. Analysis of the spectral indices along the plume structures shows slight steepening of values away from the core (α ≃ −0.8), indicative of ageing of electrons along the flow. Brighter hotspots of emission present in both north and south plumes show significantly flatter spectral indices (α ≃ −0.4). This is similar to the spectral index behaviour observed in higher energy astrophysical jets. High field strengths in the edge‐brightened regions (up to 18 μG) of the radio lobes are probably owing to compression of the frozen halo field, indicative of interaction between the ejecta driven bow shock with the ambient halo medium. Comparison with other galaxies displaying similar features suggests that although the nuclear starburst is no doubt contributing significantly to the concentration of cosmic rays in the radio lobes, a Seyfert nucleus is needed to explain the collimated jet observed in these objects.

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An Atlas of Supernova Remnant Magnetic Fields

Cited by 68 publications

References 6 publications

The Magnetohydrodynamics of Supersonic Gas Clouds: MHD Cosmic Bullets and Wind‐swept Clumps

The Magnetohydrodynamics of Supersonic Gas Clouds: MHD Cosmic Bullets and Wind‐swept Clumps

Cassiopeia A: dust factory revealed via submillimetre polarimetry

Radio continuum evidence for nuclear outflow in the Circinus galaxy

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