scholarly journals POLARIZATION SIGNATURES OF RELATIVISTIC MAGNETOHYDRODYNAMIC SHOCKS IN THE BLAZAR EMISSION REGION. I. FORCE-FREE HELICAL MAGNETIC FIELDS

2016 ◽  
Vol 817 (1) ◽  
pp. 63 ◽  
Author(s):  
Haocheng Zhang ◽  
Wei Deng ◽  
Hui Li ◽  
Markus Böttcher
Keyword(s):  
Magnetic Fields ◽  
Emission Region ◽  
Region I ◽  
Magnetohydrodynamic Shocks

scholarly journals Non-Dipolar Magnetic Fields in Pulsars

2000 ◽  
Vol 177 ◽  
pp. 377-378
Author(s):  
Jean A. Eilek ◽  
Timothy H. Hankins
Keyword(s):  
Magnetic Fields ◽  
Radio Emission ◽  
Position Angle ◽  
Field Structure ◽  
Dipole Field ◽  
Emission Region

AbstractSeveral bright pulsars have position angle sweeps which are not consistent with a simple dipole field in the radio emission region. The data are now good enough to justify modelling of deviations in the field structure in these stars, and the effect of these deviations on the radio emission. As a first step, we consider the effect of quadrupoles, and of polar currents, on the observed polarization and emission signatures.

Electrostatic particle-in-cell simulation of heat flux mitigation using magnetic fields

2016 ◽  
Vol 82 (5) ◽  
Author(s):  
Karl Felix Lüskow ◽  
S. Kemnitz ◽  
G. Bandelow ◽  
J. Duras ◽  
D. Kahnfeld ◽  
...  
Keyword(s):  
Heat Flux ◽  
Magnetic Fields ◽  
Turbulent Transport ◽  
Optical Emission ◽  
Emission Region ◽  
Transport Channel ◽  
Particle In Cell ◽  
Heat Deposition ◽  
Cell Simulation ◽  
Pic Method

The particle-in-cell (PIC) method was used to simulate heat flux mitigation experiments with partially ionised argon. The experiments demonstrate the possibility of reducing heat flux towards a target using magnetic fields. Modelling using the PIC method is able to reproduce the heat flux mitigation qualitatively. This is driven by modified electron transport. Electrons are magnetised and react directly to the external magnetic field. In addition, an increase of radial turbulent transport is also needed to explain the experimental observations in the model. Close to the target an increase of electron density is created. Due to quasi-neutrality, ions follow the electrons. Charge exchange collisions couple the dynamics of the neutrals to the ions and reduce the flow velocity of neutrals by radial momentum transport and subsequent losses. By this, the dominant heat-transport channel by neutrals gets reduced and a reduction of the heat deposition, similar to the experiment, is observed. Using the simulation a diagnostic module for optical emission is developed and its results are compared with spectroscopic measurements and photos from the experiment. The results of this study are in good agreement with the experiment. Experimental observations such as a shrank bright emission region close to the nozzle exit, an additional emission in front of the target and an overall change in colour to red are reproduced by the simulation.

scholarly journals Single Pulse Analysis of the Core-Dominated Pulsar B0611+22

2000 ◽  
Vol 177 ◽  
pp. 175-176
Author(s):  
Jeffrey S. Kern
Keyword(s):  
Single Pulse ◽  
Emission Region ◽  
Surprising Result ◽  
Polar Cap ◽  
Pulsar Radio ◽  
The Core ◽  
Dependent Behavior ◽  
Region I ◽  
Pulse Analysis ◽  
Pulsar Radio Emission

AbstractSingle pulse studies of pulsar radio emission provide a window into the time dependent behavior of the radio loud region. I have analyzed a series of precision polarimetric observations of pulsar B0611+22 to determine the geometry of the emission region. The observations are consistent with a central core emission region, and a periodically present conal component. This identification leads to the surprising result that all emission is from the leading half of the polar cap.

scholarly journals Magnetic Fields, Oscillations, and Heating in the Quiet Sun Temperature Minimum Region from Ultraviolet Observations at 1600 Å

1994 ◽  
Vol 154 ◽  
pp. 287-294
Author(s):  
J. W. Cook
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Local Heating ◽  
Temperature Minimum ◽  
Flux Tubes ◽  
Absolute Value ◽  
Region I ◽  
Period Oscillation ◽  
S Period ◽  
Ultraviolet Observations

The High Resolution Telescope and Spectrograph (HRTS) instrument has obtained broadband spectroheliograph images at 1600 Å of the solar temperature minimum region. I discuss HRTS observations of quiet areas and their relation with magnetic fields, five minute oscillations, and heating. The brightness temperature of solar fine structure elements composing the supergranular network is found to be linearly proportional to the local absolute value of magnetic field strength. There is evidence for a 250-s period oscillation occurring in 10-arcsec scale patches, which however is energetically unimportant to the local heating budget. A general nonmagnetic background heating and five minute oscillations occur globally, while the network bright points occur in magnetic regions, heated perhaps from partial dissipation of Alfvén waves (whose energy flux is linearly proportional to B) in individual elemental 1500-G (at the photosphere) flux tubes which expand to form the temperature minimum fine structure bright points.

scholarly journals Recent Advances in the Observation and Analysis of Stellar Magnetic Fields

1991 ◽  
Vol 130 ◽  
pp. 389-400
Author(s):  
Steven Saar
Keyword(s):  
Magnetic Fields ◽  
Vertical Structure ◽  
Main Sequence ◽  
Late Type ◽  
Circularly Polarized ◽  
Object A ◽  
Region I ◽  
Systematic Effects ◽  
Stellar Magnetic Fields ◽  
Improved Methods

AbstractThere has been considerable progress recently in the study of magnetic fields on late-type stars. Advances in the theory include investigation of systematic effects, new and improved methods of analysis for unpolarized and circularly polarized lines, new models of stellar dynamos and of broadband linear polarization, and the first studies of the thermodynamic nature of stellar magnetic regions and their vertical structure. Observationally, there have been new measurements, particularly of young and active stars (including the first detection of a field on a pre-main sequence object), a new monitoring campaign, the first indications of the relative temperatures in stellar plages, and the first measurements of fields in a single stellar active region. I discuss the results in the framework of stellar activity and surface structure.

scholarly journals Spectrum of Galactic Background Radiation

1974 ◽  
Vol 60 ◽  
pp. 185-186 ◽  
Author(s):  
J. R. Shakeshaft
Keyword(s):  
Magnetic Fields ◽  
Background Radiation ◽  
Radio Spectrum ◽  
Region I ◽  
Region Ii ◽  
Galactic Background

New measurements of the galactic background radiation between 151 and 1407 MHz have been made by Sironi and by Webster. The radio spectrum shows a bend at ~ 315 MHz in Bridle's Region I and ~ 100 MHz in Region II, implying magnetic fields of 7.6 µG and 2.4 µG, respectively.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

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