scholarly journals Long, depolarising Hα-filament towards the Monogem ring

2020 ◽  
Vol 641 ◽  
pp. A121
Author(s):  
Wolfgang Reich ◽  
Patricia Reich ◽  
Xiaohui Sun
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Large Scale ◽  
Local Magnetic Field ◽  
Magnetic Field Direction ◽  
X Rays ◽  
Rotation Measure ◽  
Far Ultraviolet ◽  
Screen Model ◽  
The Magnetic Field

Context. In soft X-rays, the Monogem ring is an object with a diameter of 25° located in the Galactic anti-centre. It is believed to be a faint, evolved, local supernova remnant. The ring is also visible in the far-ultraviolet, and a few optical filaments are related. It is not seen at radio wavelengths, as other large supernova remnants are. Aims. We study a narrow about 4.°5 long, faint Hα-filament, G203.7 + 11.5, that is seen towards the centre of the Monogem ring. It causes depolarisation and excessive Faraday rotation of radio polarisation data. Methods. Polarisation observations at λ11 cm and λ21 cm with the Effelsberg 100-m telescope were analysed in addition to WMAP data, extragalactic rotation measures, and Hα data. A Faraday-screen model was applied. Results. From the analysis of the depolarisation properties of the Hα filament, we derived a line-of-sight magnetic field, B||, of 26 ± 5 μG for a distance of 300 pc and an electron density, ne, of 1.6 cm−3. The absolute largest rotation measure of G203.7 + 11.5 is −86 ± 3 rad m−2, where the magnetic field direction has the opposite sign from the large-scale Galactic field. We estimated the average synchrotron emissivity at λ21 cm up to 300 pc distance towards G203.7 + 11.5 to about 1.1 K Tb/kpc, which is higher than typical Milky Way values. Conclusions. The magnetic field within G203.7 + 11.5 is unexpected in direction and strength. Most likely, the filament is related to the Monogem-ring shock, where interactions with ambient clouds may cause local magnetic field reversals. We confirm earlier findings of an enhanced but direction-dependent local synchrotron emissivity.

scholarly journals Probing interstellar magnetic fields with Supernova remnants

2008 ◽  
Vol 4 (S259) ◽  
pp. 75-80 ◽  
Author(s):  
Roland Kothes ◽  
Jo-Anne Brown
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Supernova Remnants ◽  
Large Scale ◽  
Galactic Plane ◽  
Field Configuration ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
Field Lines ◽  
The Magnetic Field

AbstractAs Supernova remnants expand, their shock waves are freezing in and compressing the magnetic field lines they encounter; consequently we can use Supernova remnants as magnifying glasses for their ambient magnetic fields. We will describe a simple model to determine emission, polarization, and rotation measure characteristics of adiabatically expanding Supernova remnants and how we can exploit this model to gain information about the large scale magnetic field in our Galaxy. We will give two examples: The SNR DA530, which is located high above the Galactic plane, reveals information about the magnetic field in the halo of our Galaxy. The SNR G182.4+4.3 is located close to the anti-centre of our Galaxy and reveals the most probable direction where the large-scale magnetic field is perpendicular to the line of sight. This may help to decide on the large-scale magnetic field configuration of our Galaxy. But more observations of SNRs are needed.

scholarly journals Simulating TeV gamma-ray morphologies of shell-type supernova remnants

2020 ◽  
Vol 498 (4) ◽  
pp. 5557-5573 ◽  
Author(s):  
Matteo Pais ◽  
Christoph Pfrommer
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Large Scale ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Local Magnetic Field ◽  
Magnetic Field Direction ◽  
Best Fitting ◽  
Gamma Ray Emission ◽  
Fitting Model

ABSTRACT Supernova remnant (SNR) shocks provide favourable sites of cosmic ray (CR) proton acceleration if the local magnetic field direction is quasi-parallel to the shock normal. Using the moving-mesh magnetohydrodynamical (MHD) code arepo we present a suite of SNR simulations with CR acceleration in the Sedov–Taylor phase that combine different magnetic field topologies, density distributions with gradients and large-scale fluctuations, and – for our core-collapse SNRs – a multiphase interstellar medium with dense clumps with a contrast of 104. Assuming the hadronic gamma-ray emission model for the TeV gamma-ray emission, we find that large-amplitude density fluctuations of δρ/ρ0 ≳ 75 per cent are required to strongly modulate the gamma-ray emissivity in a straw man’s model in which the acceleration efficiency is independent of magnetic obliquity. However, this causes strong corrugations of the shock surface that are ruled out by gamma-ray observations. By contrast, magnetic obliquity-dependent acceleration can easily explain the observed variance in gamma-ray morphologies ranging from SN1006 (with a homogeneous magnetic field) to Vela Junior and RX J1713 (with a turbulent field) in a single model that derives from plasma particle-in-cell simulations. Our best-fitting model for SN1006 has a large-scale density gradient of ∇n ≃ 0.0034 cm−3 pc−1 pointing from south-west to north-east and a magnetic inclination with the plane of the sky of ≲10°. Our best-fitting model for Vela Junior and RX J1713 adopts a combination of turbulent magnetic field and dense clumps to explain their TeV gamma-ray morphologies and moderate shock corrugations.

Radio Polarization and Magnetic Fields in Six Supernova Remnants

1989 ◽  
Vol 8 (2) ◽  
pp. 187-194 ◽  
Author(s):  
D. K. Milne ◽  
J. L. Caswell ◽  
M. J. Kesteven ◽  
R. F. Haynes ◽  
R. S. Roger
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Linear Polarization ◽  
Supernova Remnants ◽  
Magnetic Field Direction ◽  
Rotation Measure ◽  
5 Ghz ◽  
The Magnetic Field ◽  
Measure Distribution

Abstract8.4 GHz linear polarization maps, obtained with the Parkes radio telescope, are presented for six southern supernova remnants. These results are compared with published and unpublished polarization maps at 5 GHz to derive the magnetic field direction and Faraday rotation measure distribution.These results are part of a program to map the magnetic fields in galactic supernova remnants and complement our program to obtain high-resolution maps of galactic SNRs using the Molonglo Observatory Synthesis Telescope; five new Molonglo maps are presented here.

scholarly journals Connecting magnetic fields from sub-galactic scale to clusters of galaxies and beyond with cosmological MHD simulations

2015 ◽  
Vol 11 (A29B) ◽  
pp. 699-699
Author(s):  
Klaus Dolag ◽  
Alexander M. Beck ◽  
Alexander Arth
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Heat Transport ◽  
Galaxy Clusters ◽  
Large Scale ◽  
High Redshift ◽  
Galactic Halos ◽  
Rotation Measure ◽  
The Magnetic Field ◽  
Good Agreement

AbstractUsing the MHD version of Gadget3 (Stasyszyn, Dolag & Beck 2013) and a model for the seeding of magnetic fields by supernovae (SN), we performed simulations of the evolution of the magnetic fields in galaxy clusters and study their effects on the heat transport within the intra cluster medium (ICM). This mechanism – where SN explosions during the assembly of galaxies provide magnetic seed fields – has been shown to reproduce the magnetic field in Milky Way-like galactic halos (Beck et al. 2013). The build up of the magnetic field at redshifts before z = 5 and the accordingly predicted rotation measure evolution are also in good agreement with current observations. Such magnetic fields present at high redshift are then transported out of the forming protogalaxies into the large-scale structure and pollute the ICM (in a similar fashion to metals transport). Here, complex velocity patterns, driven by the formation process of cosmic structures are further amplifying and distributing the magnetic fields. In galaxy clusters, the magnetic fields therefore get amplified to the observed μG level and produce the observed amplitude of rotation measures of several hundreds of rad/m2. We also demonstrate that heat conduction in such turbulent fields on average is equivalent to a suppression factor around 1/20th of the classical Spitzer value and in contrast to classical, isotropic heat transport leads to temperature structures within the ICM compatible with observations (Arth et al. 2014).

scholarly journals Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

2020 ◽  
Vol 644 ◽  
pp. A27
Author(s):  
L. Bonne ◽  
S. Bontemps ◽  
N. Schneider ◽  
S. D. Clarke ◽  
D. Arzoumanian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Velocity Gradient ◽  
Large Scale ◽  
Transverse Velocity ◽  
Local Magnetic Field ◽  
Filament Formation ◽  
Field Orientation ◽  
Physical Conditions ◽  
The Magnetic Field

Context. Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated. Aims. We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation. Methods. We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2 12CO(1–0) map of the full Musca cloud, H I emission of the Chamaeleon-Musca complex, a Planck polarisation map, line radiative transfer models, Gaia data, and synthetic observations from filament formation simulations. Results. The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (nH2 ∼ 104 cm−3) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at T ~ 15 K and nH2 ∼ 103 cm−3 is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived from Planck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H I cloud down to the Musca filament. We also report a strong [C18O]/[13CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2 pc in a weak ambient far-ultraviolet (FUV) field. Conclusions. The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H I cloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.

scholarly journals On the generation of solitary waves observed by Cluster in the near-Earth magnetosheath

2005 ◽  
Vol 12 (2) ◽  
pp. 181-193 ◽  
Author(s):  
J. S. Pickett ◽  
L.-J. Chen ◽  
S. W. Kahler ◽  
O. Santolík ◽  
M. L. Goldstein ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solitary Waves ◽  
Bow Shock ◽  
Generation Mechanism ◽  
Local Magnetic Field ◽  
Magnetic Field Direction ◽  
Waveform Data ◽  
Background Magnetic Field ◽  
Ion Velocity ◽  
The Magnetic Field

Abstract. Through case studies involving Cluster waveform observations, solitary waves in the form of bipolar and tripolar pulses have recently been found to be quite abundant in the near-Earth dayside magnetosheath. We expand on the results of those previous studies by examining the distribution of solitary waves from the bow shock to the magnetopause using Cluster waveform data. Cluster's orbit allows for the measurement of solitary waves in the magnetosheath from about 10 RE to 19.5 RE. Our results clearly show that within the magnetosheath, solitary waves are likely to be observed at any distance from the bow shock and that this distance has no dependence on the time durations and amplitudes of the solitary waves. In addition we have found that these same two quantities show no dependence on either the ion velocity or the angle between the ion velocity and the local magnetic field direction. These results point to the conclusion that the solitary waves are probably created locally in the magnetosheath at multiple locations, and that the generation mechanism is most likely not solely related to ion dynamics, if at all. To gain insight into a possible local generation mechanism, we have examined the electron differential energy flux characteristics parallel and perpendicular to the magnetic field, as well as the local electron plasma and cyclotron frequencies and the type of bow shock that Cluster is behind, for several time intervals where solitary waves were observed in the magnetosheath. We have found that solitary waves are most likely to be observed when there are counterstreaming (~parallel and anti-parallel to the magnetic field) electrons at or below about 100eV. However, there are times when these counterstreaming electrons are present when solitary waves are not. During these times the background magnetic field strength is usually very low (<10nT), implying that the amplitudes of the solitary waves, if present, would be near or below those of other waves and electrostatic fluctuations in this region making it impossible to isolate or clearly distinguish them from these other emissions in the waveform data. Based on these results, we have concluded that some of the near-Earth magnetosheath solitary waves, perhaps in the form of electron phase-space holes, may be generated locally by a two-stream instability involving electrons based on the counterstreaming electrons that are often observed when solitary waves are present. We have not ruled out the possibility that the solitary waves could be generated as a result of the lower-hybrid Buneman instability in the presence of an electron beam, through the electron acoustic mode or through processes involving turbulence, which is almost always present in the magnetosheath, but these will be examined in a more comprehensive study in the future.

scholarly journals A tail like no other

2018 ◽  
Vol 614 ◽  
pp. A10 ◽  
Author(s):  
Martin Volwerk ◽  
Charlotte Goetz ◽  
Ingo Richter ◽  
Magda Delva ◽  
Katharina Ostaszewski ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Energy ◽  
Cone Angle ◽  
Small Scale ◽  
Main Magnetic Field ◽  
Magnetic Field Direction ◽  
Tail Structure ◽  
Comet 67P ◽  
The Magnetic Field

Context. The Rosetta Plasma Consortium (RPC) magnetometer (MAG) data during the tail excursion in March–April 2016 are used to investigate the magnetic structure of and activity in the tail region of the weakly outgassing comet 67P/Churyumov–Gerasimenko (67P). Aims. The goal of this study is to compare the large scale (near) tail structure with that of earlier missions to strong outgassing comets, and the small scale turbulent energy cascade (un)related to the singing comet phenomenon. Methods. The usual methods of space plasma physics are used to analyse the magnetometer data, such as minimum variance analysis, spectral analysis, and power law fitting. Also the cone angle and clock angle of the magnetic field are calculated to interpret the data. Results. It is found that comet 67P does not have a classical draped magnetic field and no bi-lobal tail structure at this late stage of the mission when the comet is already at 2.7 AU distance from the Sun. The main magnetic field direction seems to be more across the tail direction, which may implicate an asymmetric pick-up cloud. During periods of singing comet activity the propagation direction of the waves is at large angles with respect to the magnetic field and to the radial direction towards the comet. Turbulent cascade of magnetic energy from large to small scales is different in the presence of singing as without it.

scholarly journals 2700 MHz Polarization Observations of 17 Supernova Remnants

1974 ◽  
Vol 27 (4) ◽  
pp. 549 ◽  
Author(s):  
DK Milne ◽  
JR Dickel
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Total Power ◽  
Rotation Measure ◽  
The Magnetic Field

Maps are presented of the polarization and total-power emission at 2700 MHz from 17 supernova remnants, including the Monoceros nebula, the Lupus loop and W44. irections of the magnetic field and values of the rotation measure are deduced for W44 by ombining 2700 and 5000 MHz observations.

scholarly journals Magnetic fields in star-forming systems – II: Examining dust polarization, the Zeeman effect, and the Faraday rotation measure as magnetic field tracers

2020 ◽  
Vol 500 (1) ◽  
pp. 153-176
Author(s):  
Stefan Reissl ◽  
Amelia M Stutz ◽  
Ralf S Klessen ◽  
Daniel Seifried ◽  
Stefanie Walch
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Zeeman Effect ◽  
Dominant Factor ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Magnetic Field Direction ◽  
Rotation Measure ◽  
The Magnetic Field

ABSTRACT The degree to which the formation and evolution of clouds and filaments in the interstellar medium is regulated by magnetic fields remains an open question. Yet the fundamental properties of the fields (strength and 3D morphology) are not readily observable. We investigate the potential for recovering magnetic field information from dust polarization, the Zeeman effect, and the Faraday rotation measure (RM) in a SILCC-Zoom magnetohydrodynamic (MHD) filament simulation. The object is analysed at the onset of star formation and it is characterized by a line-mass of about $\mathrm{\left(M/L\right) \sim 63\ \mathrm{M}_{\odot }\ pc^{-1}}$ out to a radius of $1\,$ pc and a kinked 3D magnetic field morphology. We generate synthetic observations via polaris radiative transfer (RT) post-processing and compare with an analytical model of helical or kinked field morphology to help interpreting the inferred observational signatures. We show that the tracer signals originate close to the filament spine. We find regions along the filament where the angular dependence with the line of sight (LOS) is the dominant factor and dust polarization may trace the underlying kinked magnetic field morphology. We also find that reversals in the recovered magnetic field direction are not unambiguously associated to any particular morphology. Other physical parameters, such as density or temperature, are relevant and sometimes dominant compared to the magnetic field structure in modulating the observed signal. We demonstrate that the Zeeman effect and the RM recover the line-of-sight magnetic field strength to within a factor 2.1–3.4. We conclude that the magnetic field morphology may not be unambiguously determined in low-mass systems by observations of dust polarization, Zeeman effect, or RM, whereas the field strengths can be reliably recovered.

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