scholarly journals The GBT 350-MHz Drift Scan Pulsar Survey – III. Detection of a magnetic field in the eclipsing material of PSR J2256–1024

2020 ◽  
Vol 495 (3) ◽  
pp. 3052-3064
Author(s):  
Kathryn Crowter ◽  
Ingrid H Stairs ◽  
Christie A McPhee ◽  
Anne M Archibald ◽  
Jason Boyles ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Zero Magnetic Field ◽  
Line Of Sight ◽  
Black Widow ◽  
Millisecond Pulsars ◽  
X Ray ◽  
Potential Source ◽  
Rotation Measure ◽  
Drift Scan ◽  
Polarization Profiles

ABSTRACT We present the first measurement of a non-zero magnetic field in the eclipsing material of a black widow pulsar. Black widows are millisecond pulsars which are ablating their companions; therefore they are often proposed as one potential source of isolated millisecond pulsars. PSR J2256–1024 is an eclipsing black widow discovered at radio wavelengths and later also observed in the X-ray and gamma parts of the spectrum. Here we present the radio timing solution for PSR J2256–1024; polarization profiles at 350, 820, and 1500 MHz; and an investigation of changes in the polarization profile due to eclipsing material in the system. In the latter we find evidence of Faraday rotation in the linear polarization shortly after eclipse, measuring a rotation measure of 0.44(6) rad m−2 and a corresponding line-of-sight magnetic field of ∼1.11(16) mG.

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 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.

scholarly journals Magnetic-Field Vector Maps of Nearby Spiral Galaxies

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 32 ◽  
Author(s):  
Hiroyuki Nakanishi ◽  
Kohei Kurahara ◽  
Kenta Anraku
Keyword(s):  
Magnetic Field ◽  
Spiral Galaxies ◽  
Transverse Magnetic ◽  
Field Vector ◽  
Line Of Sight ◽  
Large Array ◽  
Magnetic Vector ◽  
Very Large Array ◽  
Rotation Measure ◽  
The Galaxy

We present a method for determining the directions of magnetic-field vectors in a spiral galaxy using two synchrotron polarization maps, an optical image, and a velocity field. The orientation of the transverse magnetic field is determined with a synchrotron polarization map of a higher-frequency band, and the 180 ∘ -ambiguity is solved by using a sign of Rotation Measure (RM) after determining the geometrical orientation of a disk based on an assumption of trailing spiral arms. The advantage of this method is that the direction of a magnetic vector for each line of sight throughout the galaxy can inexpensively be determined, with easily available data and simple assumptions. We applied this method to three nearby spiral galaxies using archival data obtained with a Very Large Array (VLA) to demonstrate how it works. The three galaxies have both clockwise and counterclockwise magnetic fields, which implies that none of the three galaxies is classified in a simple Axis-Symmetric type, but types of higher modes, and that magnetic reversals commonly exist.

Probing the B-fields of AGN jets on kiloparsec scales - NGC 6251

2018 ◽  
Vol 14 (S342) ◽  
pp. 244-245
Author(s):  
Sebastian Knuettel ◽  
Denise Gabuzda
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Outward Current ◽  
Electrical Current ◽  
Line Of Sight ◽  
Astrophysical Jets ◽  
Rotation Measure ◽  
Jet Structure ◽  
Helical Magnetic Field

AbstractBy constructing images of the Faraday rotation measure (RM) of large scale astrophysical jets, the line-of-sight magnetic field component and electron density in the region of Farady rotation can be investigated. A significant gradient in the RM transverse to the jet direction may indicate a corresponding gradient in the line-of-sight magnetic field, implying a toroidal or helical magnetic field, which would, in turn, imply the presence of an associated electrical current in the jet. The detection of such large scale gradients can reliably demonstrate that helical or toroidal fields can persist to large distances from the central AGN. We present a kiloparsec-scale Faraday rotation map of NGC 6251 that shows statistically significant transverse RM gradients across its kiloparsec scale jet structure that imply an outward current.

scholarly journals Synthetic observations of spiral arm tracers of a simulated Milky Way analog

2020 ◽  
Vol 642 ◽  
pp. A201 ◽  
Author(s):  
S. Reissl ◽  
J. M. Stil ◽  
E. Chen ◽  
R. G. Treß ◽  
M. C. Sormani ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Faraday Rotation ◽  
Milky Way ◽  
Line Of Sight ◽  
Unit Distance ◽  
Spiral Arms ◽  
Rotation Measure ◽  
The Magnetic Field ◽  
Spiral Arm

Context. The Faraday rotation measure (RM) is often used to study the magnetic field strength and orientation within the ionized medium of the Milky Way. Recent observations indicate an RM magnitude in the spiral arms that exceeds the commonly assumed range. This raises the question of how and under what conditions spiral arms create such strong Faraday rotation. Aims. We investigate the effect of spiral arms on Galactic Faraday rotation through shock compression of the interstellar medium. It has recently been suggested that the Sagittarius spiral arm creates a strong peak in Faraday rotation where the line of sight is tangent to the arm, and that enhanced Faraday rotation follows along side lines which intersect the arm. Here our aim is to understand the physical conditions that may give rise to this effect and the role of viewing geometry. Methods. We apply a magnetohydrodynamic simulation of the multi-phase interstellar medium in a Milky Way-type spiral galaxy disk in combination with radiative transfer in order to evaluate different tracers of spiral arm structures. For observers embedded in the disk, dust intensity, synchrotron emission, and the kinematics of molecular gas observations are derived to identify which spiral arm tangents are observable. Faraday rotation measures are calculated through the disk and evaluated in the context of different observer positions. The observer’s perspectives are related to the parameters of the local bubbles surrounding the observer and their contribution to the total Faraday rotation measure along the line of sight. Results. We reproduce a scattering of tangent points for the different tracers of about 6° per spiral arm similar to the Milky Way. For the RM, the model shows that compression of the interstellar medium and associated amplification of the magnetic field in spiral arms enhances Faraday rotation by a few hundred rad m−2 in addition to the mean contribution of the disk. The arm–interarm contrast in Faraday rotation per unit distance along the line of sight is approximately ~10 in the inner Galaxy, fading to ~2 in the outer Galaxy in tandem with the waning contrast of other tracers of spiral arms. We identify a shark fin pattern in the RM Milky Way observations and in the synthetic data that is characteristic for a galaxy with spiral arms.

scholarly journals Fluctuation dynamos and their Faraday rotation signatures

2012 ◽  
Vol 10 (H16) ◽  
pp. 400-400
Author(s):  
Pallavi Bhat ◽  
Kandaswamy Subramanian
Keyword(s):  
Magnetic Field ◽  
Simple Model ◽  
Faraday Rotation ◽  
High Field ◽  
Line Of Sight ◽  
Simulation Data ◽  
Thermal Electron ◽  
Volume Filling ◽  
Rotation Measure ◽  
The Magnetic Field

We study fluctuation dynamo (FD) action in turbulent systems like galaxy-clusters focusing on the Faraday rotation signature. This is defined as RM = K ∫LneB ⋅ dl where ne is the thermal electron density, B is the magnetic field, the integration is along the line of sight from the source to the observer, and K = 0.81 rad m−2 cm−3 μG−1 pc−1. We directly compute, using the simulation data, ∫ B ⋅ dl, and hence the Faraday rotation measure (RM) over 3N2 lines of sight, along each x, y and z-directions. We normalise the RM by the rms value expected in a simple model, where a field of strength Brms fills each turbulent cell but is randomly oriented from one turbulent cell to another. This normalised RM is expected to have a nearly zero mean but a non-zero dispersion, σRM. We show in Fig. 1a and 1b, that a suite of simulations, on saturation, obtain the value of σRM = 0.4−0.5, and this is independent of PM, RM and the resolution of the run. This is a fairly large value for an intermittent random field; as it is of order 40%–50%, of that expected in a model where Brms strength fields volume fill each turbulent cell, but are randomly oriented from one cell to another. We also find that the regions with a field strength larger than 2Brms contribute only 15–20% to the total RM (see Fig. 1a). This shows that it is the general ‘sea’ of volume filling fluctuating fields that contribute dominantly to the RM produced, rather than the the high field regions.

Preparation of Fibrous Bi(Pb)-Sr-Ca-Cu-O Crystals Containing the High-Tc Phase

1989 ◽  
Vol 169 ◽  
Author(s):  
I. Matsubara ◽  
H. Tanigawa ◽  
T. Ogura ◽  
H. Yamashita ◽  
M. Kinoshita ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Volume Fraction ◽  
Zero Magnetic Field ◽  
High Tc ◽  
X Ray ◽  
High Tc Phase ◽  
Zero Resistance ◽  
Resistance State ◽  
Oxygen Gas ◽  
T Phase

AbstractFibrous crystals containing the high-Tc phase (2223 phase) of the Bi(Pb)-Sr-Ca-Cu-O superconductor have been prepared by heating a glassy melt-quenched plate in a stream of oxygen gas. Each fiber is composed of several platelike single crystals which are stacked in a layered structure. The fibers show two stepdrops in resistance at 105K and 73K, and a zero-resistance state around 70K. From the results of SQUID measurements, the volume fraction of the high-T phase is found to be about 0.6%. The high-Tc phase is also detected with a microarea X-ray diffractometer, and it is stacked in the interlayer between the low-Tc platelike crystals. For the fibrous Bi-Sr-Ca-Cu-Li-O crystals, the volume fraction of the high-Tc phase increases to 1.5% and a zero resistance state is achieved at 81K. The Jc value of the Li doped fiber is 30,000A/cm2 at 77K and 300,000A/cm2 at 66K in a zero magnetic field.

scholarly journals The magnetic field strength in the Large Magellanic Cloud

1991 ◽  
Vol 148 ◽  
pp. 101-102
Author(s):  
M.E. Costa ◽  
P. M. McCulloch ◽  
P. A. Hamilton
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Large Magellanic Cloud ◽  
Radio Pulsar ◽  
Line Of Sight ◽  
The Sun ◽  
A Value ◽  
Rotation Measure ◽  
The Magnetic Field

We have measured a value of 4±5m--2rad for the rotation measure of the radio pulsar PSR0529-66 in the LMC and, after allowing for the dispersion and rotation measures of our Galaxy on the pulsar's line of sight, we deduce that the magnetic field strength in the LMC is in the range 0 to 5μGauss oriented away from the Sun.

scholarly journals Chandra observations of black widow pulsars

2012 ◽  
Vol 8 (S291) ◽  
pp. 389-391 ◽  
Author(s):  
P. Gentile ◽  
M. McLaughlin ◽  
M. Roberts ◽  
F. Camilo ◽  
J. Hessels ◽  
...  
Keyword(s):  
Power Law ◽  
Gamma Ray ◽  
The Other ◽  
Emission Characteristic ◽  
Black Widow ◽  
Millisecond Pulsars ◽  
X Ray ◽  
Significant Variability ◽  
Binary Orbit

AbstractWe describe the first X-ray observations of binary millisecond pulsars PSR J0023+0923, J1810+1744, J2215+5135, and J2256−1024. All are Fermi gamma-ray sources and three are ‘black-widow’ pulsars, with companions of mass < 0.1 M⊙. Data were taken using the Chandra X-Ray Observatory and covered a full binary orbit for each pulsar. PSRs J2215+5135 and J2256−1024, show significant orbital variability and X-ray flux minima coinciding with eclipses seen at radio wavelengths. This is consistent with intrabinary shock emission characteristic of black-widow pulsars. The other two pulsars, PSRs J0023+0923 and J1810+1744, do not demonstrate significant variability, but are fainter than the other two sources. Spectral fits yield power-law indices that range from 1.4 to 2.3 and blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135 shows a significant hard X-ray component (41% of counts are above 2 keV), which is additional evidence for the presence of intrabinary shock emission.

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