Magnetic field in the Galactic Centre: Rotation Measure observations of extragalactic sources

2007 ◽  
pp. 41-46
Author(s):  
Subhashis Roy ◽  
A. Pramesh Rao ◽  
Ravi Subrahmanyan
Keyword(s):  
Magnetic Field ◽  
Galactic Centre ◽  
Rotation Measure

scholarly journals On the magnetoionic environments of fast radio bursts

2020 ◽  
Vol 499 (1) ◽  
pp. 355-361 ◽  
Author(s):  
Wei-Yang Wang ◽  
Bing Zhang ◽  
Xuelei Chen ◽  
Renxin Xu
Keyword(s):  
Magnetic Field ◽  
Mean Value ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Host Galaxies ◽  
Surface Magnetic Field ◽  
Rotation Measure ◽  
The Mean

ABSTRACT Observations of the Faraday rotation measure, combined with the dispersion measure, can be used to infer the magnetoionic environment of a radio source. We investigate the magnetoionic environments of fast radio bursts (FRBs) by deriving their estimated average magnetic field strengths along the line of sight 〈B∥〉 in their host galaxies and comparing them with those of Galactic pulsars and magnetars. We find that for those FRBs with RM measurements, the mean 〈B∥〉 are $1.77^{+9.01}_{-1.48}\, \rm \mu G$ and $1.74^{+14.82}_{-1.55}\, \rm \mu G$ using two different methods, which is slightly larger but not inconsistent with the distribution of Galactic pulsars, $1.00^{+1.51}_{-0.60}\, \rm \mu G$. Only six Galactic magnetars have estimated 〈B∥〉. Excluding PSR J1745–2900 that has an anomalously high value due to its proximity with the Galactic Centre, the other five sources have a mean value of $1.70\, \rm \mu G$, which is statistically consistent with the 〈B∥〉 distributions of both Galactic pulsars and FRBs. There is no apparent trend of evolution of magnetar 〈B∥〉 as a function of age or surface magnetic field strength. Galactic pulsars and magnetars close to the Galactic Centre have relatively larger 〈B∥〉 values than other pulsars/magnetars. We discuss the implications of these results for the magnetoionic environments of FRB 121102 within the context of magnetar model and the model invoking a supermassive black hole, and for the origin of FRBs in general.

Magnetic field in the Galactic Centre: Rotation Measure observations of extragalactic sources

2003 ◽  
Vol 324 (S1) ◽  
pp. 41-46 ◽  
Author(s):  
Subhashis Roy ◽  
A. Pramesh Rao ◽  
Ravi Subrahmanyan
Keyword(s):  
Magnetic Field ◽  
Galactic Centre ◽  
Rotation Measure

STATIONARY SHEATH OF FARADAY ROTATION IN THE JET OF 3C 120

2010 ◽  
Vol 19 (06) ◽  
pp. 917-922
Author(s):  
JOSÉ L. GÓMEZ ◽  
MAR ROCA-SOGORB ◽  
IVÁN AGUDO ◽  
ALAN P. MARSCHER ◽  
SVETLANA G. JORSTAD
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Radio Galaxy ◽  
External Medium ◽  
Degree Of Polarization ◽  
Polarization Structure ◽  
Rotation Measure ◽  
Helical Magnetic Field ◽  
3C 120 ◽  
Two Fluid

We present a sequence of 12 monthly polarimetric multi-frequency VLBA observations of the radio galaxy 3C 120. The motion of multiple superluminal components allows the mapping of the polarization structure along most of the jet and across its width, revealing a coherent in time Faraday screen and RM-corrected polarization angles. Gradients in Faraday rotation and degree of polarization across the jet are observed, together with a localized region of high rotation measure superposed on this structure. This is explained as produced by the presence of a helical magnetic field in a two-fluid jet model, consisting of an inner emitting jet and a sheath containing nonrelativistic electrons. Interaction of the jet with the external medium would explain the confined region of enhanced Faraday rotation.

scholarly journals Magnetized filament models for diverging plasma lenses

2020 ◽  
Vol 493 (2) ◽  
pp. 1736-1752
Author(s):  
Adam Rogers ◽  
Abdul Mohamed ◽  
Bailey Preston ◽  
Jason D Fiege ◽  
Xinzhong Er
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Volume Density ◽  
Magnetized Plasma ◽  
Gravitational Lens ◽  
Line Of Sight ◽  
Density Distributions ◽  
Rotation Measure ◽  
Spherical Plasma ◽  
Helical Magnetic Field

ABSTRACT Spherical plasma lens models are known to suffer from a severe overpressure problem, with some observations requiring lenses with central pressures up to millions of times in excess of the ambient interstellar medium. There are two ways that lens models can solve the overpressure problem: a confinement mechanism exists to counter the internal pressure of the lens, or the lens has a unique geometry, such that the projected column-density appears large to an observer. This occurs with highly asymmetric models, such as edge-on sheets or filaments, with potentially low volume–density. In the first part of this work we investigate the ability of non-magnetized plasma filaments to mimic the magnification of sources seen behind spherical lenses and we extend a theorem from gravitational lens studies regarding this model degeneracy. We find that for plasma lenses, the theorem produces unphysical charge density distributions. In the second part of the work, we consider the plasma lens overpressure problem. Using magnetohydrodynamics, we develop a non self-gravitating model filament confined by a helical magnetic field. We use toy models in the force-free limit to illustrate novel lensing properties. Generally, magnetized filaments may act as lenses in any orientation with respect to the observer, with the most high-density events produced from filaments with axes near the line of sight. We focus on filaments that are perpendicular to the line of sight that show the toroidal magnetic field component may be observed via the lens rotation measure.

scholarly journals MAGMO: polarimetry of 1720-MHz OH masers towards southern star-forming regions

2020 ◽  
Vol 493 (1) ◽  
pp. 199-233 ◽  
Author(s):  
C S Ogbodo ◽  
J A Green ◽  
J R Dawson ◽  
S L Breen ◽  
S A Mao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Ground State ◽  
Supernova Remnants ◽  
Galactic Centre ◽  
Galactic Magnetic Field ◽  
Field Orientation ◽  
Star Forming ◽  
Star Forming Regions ◽  
Methanol Masers

ABSTRACT From targeted observations of ground-state hydroxyl (OH) masers towards 702 Methanol Multibeam survey 6.7-GHz methanol masers, in the Galactic longitude range from 186° through the Galactic Centre to 20°, made as part of the ‘MAGMO’ (Mapping the Galactic Magnetic field through OH masers) project, we present the physical and polarization properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star-forming regions (SFRs). In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from −11.4 to +13.2 mG, and a median magnetic field strength of |BLOS| ∼ 6 mG. With limited statistics, we present the in situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers, and water masers, and compare maser positions with mid-infrared images of the parent SFRs. Of the 33 1720-MHz star formation masers, 10 are offset from their central exciting sources, and appear to be associated with outflow activity.

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 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.

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