scholarly journals High cadence, linear, and circular polarization monitoring of OJ 287

2018 ◽  
Vol 619 ◽  
pp. A88 ◽  
Author(s):  
I. Myserlis ◽  
S. Komossa ◽  
E. Angelakis ◽  
J. L. Gómez ◽  
V. Karamanavis ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Flux Density ◽  
Total Flux ◽  
Optical Data ◽  
Arc Length ◽  
Polarization Data ◽  
Emission Component ◽  
Polarized Emission ◽  
Optical Flare

Aims. We present a multifrequency, dense radio monitoring program of the blazar OJ 287 using the 100-m Effelsberg radio telescope. The program aims to test different binary supermassive black hole (SMBH) scenarios and studying the physical conditions in the central region of this bright blazar. Here, we analyze the evolution in total flux density, linear and circular polarization as a means to study the OJ 287 jet structure and its magnetic field geometry. Methods. We used a recently developed, high-precision data analysis methodology to recover all four Stokes parameters. We measured the total flux density of OJ 287 at nine bands from 2.64 GHz to 43 GHz, the linear polarization parameters at four bands between 2.64 GHz and 10.45 GHz, and the circular polarization at two bands, 4.85 GHz and 8.35 GHz. The mean cadence of our measurements is ten days. Results. Between December 2015 and January 2017 (MJD 57370–57785), OJ 287 showed flaring activity and complex linear and circular polarization behavior. The radio electric vector position angle (EVPA) showed a large clockwise (CW) rotation by ∼340° with a mean rate of −1.04°/day. Based on concurrent very long baseline interferometric (VLBI) polarization data at 15 GHz and 43 GHz, the rotation seems to originate within the jet core at 43 GHz (projected angular size ≤0.15 mas or 0.67 pc at the redshift of the source). Moreover, optical polarization data show a similar monotonic CW rotation with a rate of about −1.1°/day which is superposed with shorter and faster rotations that exhibit rates of about 7.8°/day, mainly in the CW sense. Conclusions. The flux density and polarization variability of the single dish, VLBI and optical data is consistent with a polarized emission component propagating on a helical trajectory within a bent jet. We constrained the helix arc length to 0.26 pc and radius to ≤0.04 pc as well as the jet bending arc length projected on the plane of the sky to ≤1.9–7.6 pc. A similar bending has been observed also in high angular resolution VLBI images of the OJ 287 jet at its innermost regions. The helical trajectory covers only a part of the jet width, possibly its spine. In addition, our results indicate the presence of a stable polarized emission component. Its EVPA (−10°) is oriented perpendicular to the large scale jet, suggesting dominance of the poloidal magnetic field component. Finally, the EVPA rotation begins simultaneously with an optical flare and hence the two might be physically connected. That optical flare has been suggested to be linked to the interaction of a secondary SMBH with the inner accretion disk or originating in the jet of the primary.

scholarly journals Highly polarized burst of a water maser in Orion-KL

2002 ◽  
Vol 206 ◽  
pp. 92-95
Author(s):  
Shinji Horiuchi ◽  
Osamu Kameya
Keyword(s):  
Magnetic Field ◽  
Flux Density ◽  
Strong Magnetic Field ◽  
Radio Telescope ◽  
Linear Polarization ◽  
Total Flux ◽  
Star Forming ◽  
Intensity Decrease ◽  
Density Decrease ◽  
Water Maser

It has been reported that the 22 GHz water maser in the star forming region Orion-KL has started an outburst in rate 1997 (Omodaka et al. 1998, IAUC 6893). Using Mizusawa radio telescope we started a monitoring observation of the bursting maser. We measured the linear polarization of the maser after the burst, during a phase of rapid flux density decrease. We find that the total flux density of 2.4 × 106 Jy (December 1998) exhibits about 46% linear polarization. Over the next six months we find that the total intensity decrease about two orders of magnitude while the fractional linear polarization gradually fell to 30%. These results suggest that the present bursting phenomenon has an origin similar to the super maser event starting in 1979, and the phenomenon of the extremely bright masers in this region is geometric in nature and related to the strong magnetic field.

Application of the Dipole Model to Selected Magnetic White Dwarfs

1989 ◽  
Vol 8 (2) ◽  
pp. 148-153 ◽  
Author(s):  
N. Achilleos ◽  
D. T. Wickramasinghe
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Observational Data ◽  
White Dwarfs ◽  
Zeeman Splitting ◽  
Polarization Data ◽  
Detailed Model ◽  
Field Geometry ◽  
Hydrogen Lines ◽  
The Magnetic Field

AbstractVarious authors have reported observations of the flux and circular polarization for the three stars PG 1658 + 441, PG 1533 − 057 and K 813 − 14. On the basis of the observational data, the stars were classified as magnetic white dwarfs. To place constraints on the magnetic field strengths and geometries of these stars, the relevant authors qualitatively compared the data with available theory and, in two cases, used a model of optically thin hydrogen threaded by a magnetic field.In this paper we use a more detailed model for magnetic white dwarfs to assess the results previously obtained for these three stars. We find that, in two cases, the observed spectra can be explained by the Zeeman splitting of hydrogen lines in a stellar magnetic field which takes the form of a dipole situated at the centre of the star. The circular polarization data for PG 1658 + 441, however, may indicate a field geometry for this star which is significally different from that of a centred dipole.

Search for Zeeman-splitting of OH 6.035 GHz line in the young planetary nebula K 3-35

2020 ◽  
Vol 495 (4) ◽  
pp. 4326-4333
Author(s):  
L G Hou ◽  
X Y Gao
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Planetary Nebula ◽  
Zeeman Splitting ◽  
Line Of Sight ◽  
State Transitions ◽  
Frequency Shifts ◽  
Left Hand ◽  
Emission Component ◽  
Source Of Information

ABSTRACT Magnetic field could play a role in the formation and early evolution of non-spherical planetary nebulae (PNe). The predominant source of information of the magnetic fields in PNe is the polarization observations of maser emission. To date, distinct and/or possible Zeeman pairs have only been reported towards four PNe by measuring the OH ground-state transitions at 1.6–1.7 GHz. With the C-band (4–8 GHz) receiving system of the Shanghai TianMa 65-m radio telescope, we aim to search for possible Zeeman pairs of the PNe towards which the OH excited-state 6.035 GHz maser lines have been detected. For the young PN K 3-35, a new emission component near VLSR = 20.5 km s−1, which is currently the strongest (Ipeak ∼ 0.3 Jy) among the four components towards K 3-35 is detected. A clear S-shaped feature corresponding to this new emission component is observed in the Stokes V spectrum. Frequency shifts are seen between the fitted left-hand circular polarization and right-hand circular polarization emission peaks for the two emission components near VLSR = 19.7 and 20.5 km s−1. If the S-shaped profile and the frequency shifts are the results of Zeeman-splitting, the line-of-sight magnetic field strengths of +2.9 ± 0.6 and +4.5 ± 0.4 mG can be inferred for these two emission components, respectively.

scholarly journals Curvature radiation in rotating pulsar magnetosphere

2012 ◽  
Vol 8 (S291) ◽  
pp. 552-554
Author(s):  
P. F. Wang ◽  
C. Wang ◽  
J. L. Han
Keyword(s):  
Magnetic Field ◽  
Circular Polarization ◽  
Field Line ◽  
Pulsar Magnetosphere ◽  
Curvature Radiation ◽  
Line Region ◽  
Open Field Line ◽  
Polarized Emission ◽  
Field Lines ◽  
Relativistic Particles

AbstractWe investigate the curvature radiation from relativistic particles streaming along magnetic field lines and co-rotating with a pulsar. The co-rotation affects the trajectories of the particles and hence the emission properties, especially the polarization. For three density models in the form of core, cone and patches, we calculate the polarized emission at a given height and also the integrated emission for the whole open field line region, and try to explain the generation of circular polarization.

scholarly journals The Westerbork Northern Sky Survey

1996 ◽  
Vol 175 ◽  
pp. 495-498
Author(s):  
A.G. DE BRUYN
Keyword(s):  
Circular Polarization ◽  
Flux Density ◽  
Spatial Resolution ◽  
Radio Telescope ◽  
Noise Level ◽  
Polarization Data ◽  
Sky Survey

The WEsterbork Northern Sky Survey (WENSS) is a large–sky survey being carried out at 92 and 49 cm with the Westerbork Synthesis Radio Telescope (WSRT). At 92 cm WENSS will cover the sky north of declination +30° (an area of 10,000 square degrees) to a limiting (5σ) flux density of about 15-20 mJy. Both linear and circular polarization data is obtained. The polarization images have a noise level of about 2 mJy (lσ). The spatial resolution at 92 cm is about 1′. At 49 cm about one fifth of this area will be covered to somewhat lower flux density and with twice the resolution. The resulting catalogue will contain about 250,000 sources at 92 cm and 30,000 sources at 49 cm.

Magnetic-field strengths from optical polarization data

1967 ◽  
Vol 31 ◽  
pp. 381-383
Author(s):  
J. M. Greenberg
Keyword(s):  
Magnetic Field ◽  
Optical Polarization ◽  
Polarization Data ◽  
Term Model ◽  
Source Of Information ◽  
Field Strengths

Van de Hulst (Paper 64, Table 1) has marked optical polarization as a questionable or marginal source of information concerning magnetic field strengths. Rather than arguing about this–I should rate this method asq+-, or quarrelling about the term ‘model-sensitive results’, I wish to stress the historical point that as recently as two years ago there were still some who questioned that optical polarization was definitely due to magnetically-oriented interstellar particles.

A novel analytical calculation of magnetic field in the slotted air gap of spoke-type permanent-magnet machines using conformal mapping

2020 ◽  
pp. 1-15
Author(s):  
Jianqi Li ◽  
Yu Zhou ◽  
Jianying Li
Keyword(s):  
Magnetic Field ◽  
Conformal Mapping ◽  
Permanent Magnet ◽  
Flux Density ◽  
Analytical Method ◽  
Electromotive Force ◽  
Analytical Calculation ◽  
Air Gap ◽  
Permanent Magnet Machines ◽  
Peak Value

This paper presented a novel analytical method for calculating magnetic field in the slotted air gap of spoke-type permanent-magnet machines using conformal mapping. Firstly, flux density without slots and complex relative air-gap permeance of slotted air gap are derived from conformal transformation separately. Secondly, they are combined in order to obtain normalized flux density taking account into the slots effect. The finite element (FE) results confirmed the validity of the analytical method for predicting magnetic field and back electromotive force (BEMF) in the slotted air gap of spoke-type permanent-magnet machines. In comparison with FE result, the analytical solution yields higher peak value of cogging torque.

scholarly journals Design of a New 1D Halbach Magnet Array with Good Sinusoidal Magnetic Field by Analyzing the Curved Surface

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2522
Author(s):  
Guangdou Liu ◽  
Shiqin Hou ◽  
Xingping Xu ◽  
Wensheng Xiao
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Permanent Magnet ◽  
Flux Density ◽  
Permanent Magnets ◽  
Air Gap ◽  
Curved Surface ◽  
Magnetic Flux Density ◽  
Sinusoidal Magnetic Field ◽  
The Magnetic Field

In the linear and planar motors, the 1D Halbach magnet array is extensively used. The sinusoidal property of the magnetic field deteriorates by analyzing the magnetic field at a small air gap. Therefore, a new 1D Halbach magnet array is proposed, in which the permanent magnet with a curved surface is applied. Based on the superposition of principle and Fourier series, the magnetic flux density distribution is derived. The optimized curved surface is obtained and fitted by a polynomial. The sinusoidal magnetic field is verified by comparing it with the magnetic flux density of the finite element model. Through the analysis of different dimensions of the permanent magnet array, the optimization result has good applicability. The force ripple can be significantly reduced by the new magnet array. The effect on the mass and air gap is investigated compared with a conventional magnet array with rectangular permanent magnets. In conclusion, the new magnet array design has the scalability to be extended to various sizes of motor and is especially suitable for small air gap applications.

scholarly journals A circular polarization survey for radio stars with the Australian SKA Pathfinder

2021 ◽  
Vol 502 (4) ◽  
pp. 5438-5454
Author(s):  
Joshua Pritchard ◽  
Tara Murphy ◽  
Andrew Zic ◽  
Christene Lynch ◽  
George Heald ◽  
...  
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Flux Density ◽  
Wide Band ◽  
M Dwarfs ◽  
Square Kilometre Array ◽  
Population Statistics ◽  
Chemically Peculiar ◽  
Radio Stars

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

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