scholarly journals Summary

1974 ◽  
Vol 3 ◽  
pp. 493-498
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Radio Emission ◽  
Rotation Axis ◽  
Radiation Belts ◽  
Main Magnetic Field ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Pulsar Radiation ◽  
Wide Range

Professor G. R. A. Ellis reviewed the wide range of radio emission from Jupiter. At centimetric wavelengths the thermal radiation corresponds to a blackbody at 130K. Between 2 m and 10 cm wavelength there is a powerful component of synchrotron radiation from the electrons trapped in the radiation belts. At longer wavelengths there is a great variety of impulsive radio emission from coherent plasma oscillations.The magnetic field of Jupiter is known from the polarisation of the synchrotron radiation to be situated centrally (within one tenth of the radius) and inclined at 10° to the rotation axis. The radiating electrons have energies of the order of 10 MeV, and a density of 10”-3 cm-3, much greater than in the case of the Earth’s radiation belts.The decametric radiation varies with the rotation of Jupiter, possibly analogously to pulsar radiation. Bursts at around 4 MHz reach very high brightness temperatures, exceeding 1017 K. The occurrence of these strong bursts is closely related to the position of the Jovian satellite Io, which must have an interaction with the main magnetic field.

scholarly journals Solar activity and solar oscillations

1997 ◽  
Vol 181 ◽  
pp. 277-285
Author(s):  
Y. Elsworth
Keyword(s):  
Magnetic Field ◽  
Solar Activity ◽  
Radio Emission ◽  
Surface Temperature ◽  
The Sun ◽  
Solar Oscillations ◽  
Thermal Component ◽  
X Ray ◽  
Convective Flows ◽  
Wide Range

Helioseismology provides us with the tools to probe solar activity. So that we can consider how the solar oscillations are influenced by that activity, we first consider the phenomena that we associate with the active Sun. The surface of the Sun is not quiet but shows evidence of convection on a wide range of scales from a few hundred kilometres through to several tens-of-thousands of kilometres. The surface temperature shows signs of the convection structures with the temperature in the bright granules being some 100 K to 200 K hotter than the surrounding dark lanes. Sunspots, which are regions of high magnetic field that suppress convective flows, are clearly visible to even quite crude observations. They are several tens-of-thousands of kilometres in diameter and about 2000 K cooler than their surroundings. Ultraviolet and X-ray pictures from satellites show that the higher layers of the solar atmosphere are very non-uniform with bright regions of high activity. Contemporaneous magnetograms show that these regions are associated with sunspots. Flares - regions of magnetic reconnections - are seen at all wavelengths from X-ray through the visible to radio. They are the non-thermal component of the radio emission of the Sun. There are many other indicators of activity on the Sun.

A Gyro-Synchrotron Maser in the Solar Corona?

1978 ◽  
Vol 3 (3) ◽  
pp. 231-233 ◽  
Author(s):  
D. B. Melrose ◽  
S. M. White
Keyword(s):  
Synchrotron Radiation ◽  
Solar Corona ◽  
Brightness Temperature ◽  
Early Phase ◽  
Relativistic Electrons ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Type Iv ◽  
Alternative Suggestion ◽  
Lower Frequencies

Stewart (1978) has reported four moving type IV bursts observed with the Culgoora radio heliograph at 43, 80 and 160 MHz. After an early phase, the brightness temperatures of the observed bursts decreased with increasing frequency and with time. The highest brightness temperature observed at 43 MHz was 1010K, and it seems that the brightness temperature would have been still higher at even lower frequencies. Existing theoretical ideas on moving type IV bursts are based on data (at 80 MHz primarily) which included no brightness temperatures in excess of 109K. the accepted interpretation involved gyro-synchrotron radiation from mildly relativistic electrons (energies ≈ 100 keV); reabsorption by the electrons themselves restricts the brightness temperature to less than about 100 keV ≈ 109K (Wild and Smerd 1972, Dulk 1973). Stewart’s (1978) new data at 43 MHz require that this accepted interpretation be modified; he has suggested that higher energy electrons are involved. An alternative suggestion is explored here, namely that the absorption might be negative. In other words, the high brightness temperatures observed could be due to a gyro-synchrotron maser involving electrons with energies of about 100 keV.

scholarly journals The Formation of Discontinuities in Gas Flows in the ISM and its Relation to the Galactic Synchrotron Radio Emission

1990 ◽  
Vol 140 ◽  
pp. 159-162
Author(s):  
V.G. Berman ◽  
L.S. Marochnik ◽  
Yu.N. Mishurov ◽  
A.A. Suchkov
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Radio Emission ◽  
Large Scale ◽  
Field Energy ◽  
Gas Flows ◽  
Interstellar Gas ◽  
Gas Density ◽  
Magnetic Field Energy ◽  
Wide Range

We show that large–scale motions of the interstellar gas, such as those associated with galactic density waves, easily develop, over a wide range of scales, shocks and discontinuities which are expected to generate turbulence. The latter is supposed to evoke diffusion of magnetic fields and cosmic rays on scales down to a few parsecs. We suggest that these processes may be of major importance in discussions of interconnections between the observed radio emission of the disks of spiral galaxies and the gas density distribution within them. In particular, we predict that the density of cosmic rays and magnetic field energy must be much less contrasted (on scales of ~1 pc and up to the scales of galactic shocks) than the gas density, hence the synchrotron radio emission is not as contrasted as is predicted under the hypothesis of a fully frozen-in magnetic field.

scholarly journals Unravelling the complex magnetosphere of the B star HD 133880 via wideband observation of coherent radio emission

2020 ◽  
Vol 499 (1) ◽  
pp. 702-709
Author(s):  
Barnali Das ◽  
Poonam Chandra ◽  
Gregg A Wade
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Rotation Axis ◽  
Time Lag ◽  
Wide Frequency Range ◽  
Very Large Array ◽  
Magnetic Field Axis ◽  
Cyclotron Maser ◽  
Magnetic Stars ◽  
The Magnetic Field

ABSTRACT HD 133880 is one of the six hot magnetic stars known to produce coherent pulsed radio emission by the process of electron cyclotron maser emission (ECME). In this paper, we present observations of ECME from this star over a wide frequency range, covering nearly 300–4000 MHz with the Giant Metrewave Radio Telescope (GMRT) and the Karl G. Jansky Very Large Array (VLA). This study, which is the first of its kind, has led to the discovery of several interesting characteristics of the phenomenon and also of the host star. We find that the observable properties of ECME pulses, e.g. the time lag between right and left circularly polarized pulses, the amplitudes of the pulses, and their upper cut-off frequencies, appear to be dependent on the stellar orientation with respect to the line of sight. We suggest that all these phenomena, which are beyond the ideal picture, can be attributed to a highly azimuthally asymmetric matter distribution in the magnetosphere about the magnetic field axis, which is a consequence of both the high obliquity (the angle between rotation axis and the magnetic field axis) of the star and the deviation of the stellar magnetic field from a dipolar topology.

scholarly journals An Update on Radio Supernovae

1998 ◽  
Vol 164 ◽  
pp. 357-358 ◽  
Author(s):  
Schuyler D. Van Dyk ◽  
Richard A. Sramek ◽  
Kurt W. Weiler ◽  
Marcos J. Montes ◽  
Nino Panagia
Keyword(s):  
Synchrotron Radiation ◽  
Radio Emission ◽  
Brightness Temperature ◽  
Power Law ◽  
Progress Report ◽  
Light Curves ◽  
High Brightness ◽  
Turn On ◽  
Distance Indicators ◽  
Circumstellar Environment

AbstractThe radio emission from supernovae (SNe) is nonthermal synchrotron radiation of high brightness temperature, with a “turn-on” delay at longer wavelengths, power-law decline after maximum with index β, and spectral index α asymptotically decreasing with time to a final, optically thin value. Radio supernovae (RSNe) are best described by the Chevalier (1982) “mini-shell” model, with modifications by Weiler et al. (1990). RSNe observations provide a valuable probe of the SN circumstellar environment and constraints on progenitor masses. We present a progress report on a number of recent RSNe, as well as on new behavior from RSNe 1979C and 1980K, and on RSNe as potential distance indicators. In particular, we present updated radio light curves for SN 1993J in M81.

Observations of High Brightness Temperatures in Moving Type IV Solar Radio Bursts

1978 ◽  
Vol 3 (4) ◽  
pp. 247-249 ◽  
Author(s):  
R. T. Stewart ◽  
R. A. Duncan ◽  
S. Suzuki ◽  
G. J. Nelson
Keyword(s):  
Synchrotron Radiation ◽  
Second Phase ◽  
Synchrotron Emission ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
High Brightness ◽  
Fast Electrons ◽  
Circularly Polarized ◽  
Brightness Temperatures ◽  
Type Iv

It has generally been accepted that moving type IV bursts are generated as synchrotron radiation from energetic electrons high in the solar corona (Boischot and Denisse 1957). At 80 MHz the peak brightness temperature is usually ~ 108 K and the radiation becomes highly circularly polarized as the burst decays. This has led several authors (Kai 1969; Dulk 1970, 1973; Schmahl 1972; Robinson 1974, 1977; Nelson 1977) to the conclusion that the radiation comes from mildly relativistic (~ 100 keV) electrons and occurs at low harmonics of the gyro-frequency (gyro-synchrotron radiation). We present evidence of moving type IV bursts at 43, 80 and 160 MHz with brightness temperatures of ~ 109 K, and one at 43 MHz as high as 1010 K. The number (~ 1033) of energetic (≥ 1 MeV) electrons which is required in order to explain such high brightness temperatures by incoherent gyro-synchrotron emission is very large and near the upper limit for the number of fast electrons accelerated in the second phase of a solar flare. If amplification takes place a smaller number of electrons with energies ~ 100 keV would be required.

scholarly journals On the pulsar radiation mechanism

1996 ◽  
Vol 160 ◽  
pp. 185-186
Author(s):  
R. T. Gangadhara
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Field Line ◽  
Centrifugal Force ◽  
Radiation Mechanism ◽  
One Dimensional ◽  
Pulsar Radiation ◽  
Field Lines ◽  
Perpendicular Component ◽  
Field Strengths

Pulsars have typical magnetic field strengths between 108and 1012G. Therefore, even if the particles are produced with nonzero perpendicular component of velocity at the pole, they radiate out this component quickly due to synchrotron radiation. Therefore, the motion of a particle along a field line becomes one dimensional in regions where filed lines are straight. However, when they move along the curved magnetic field lines, they get accelerated due to the centrifugal force. They gain again the perpendicular energy at the expense of parallel energy, but can not gyrate in the curved field lines and hence do not experience any curvature or gradient drifts.

scholarly journals 3.6 cm VLBI Total Intensity and Polarization Images of BL Lacertae Objects

1996 ◽  
Vol 175 ◽  
pp. 51-52
Author(s):  
D.C. Gabuzda ◽  
A.B. Pushkarev ◽  
T.V. Cawthorne
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Radio Emission ◽  
Line Emission ◽  
Optical Emission ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
Distinguishing Features ◽  
The Magnetic Field ◽  
Magnetic Field Transverse

The major distinguishing features of BL Lacertae Objects are weak or absent line emission and strong and variable optical, infrared, and radio polarization (Angel and Stockman 1980; Kollgaard 1994). The radio emission and much of the optical emission is believed to be synchrotron radiation. There are now some 20 BL Lacertae objects for which VLBI polarization (VLBP) images have been made at λ = 6 cm (Gabuzda et al. 1994 and references therein). In nearly every BL Lacertae object in which polarization structure has been detected, the polarization position angles in knots in the jets are nearly parallel to the VLBI structural axis. Assuming the jet components to be optically thin, the magnetic fields inferred by this orientation are nearly perpendicular to the direction of the jet; perhaps the most natural interpretation of this is that the knots are associated with shocks that compress an initially tangled magnetic field as they propagate down the VLBI jet, enhancing the magnetic field transverse to the compression (Laing 1980; Hughes, Aller, & Aller 1989).

scholarly journals Maser Theory of Pulsar Radiation

1971 ◽  
Vol 46 ◽  
pp. 414-428
Author(s):  
Hong-Yee Chiu
Keyword(s):  
Radio Emission ◽  
Plasma Emission ◽  
Emission Mechanism ◽  
Radio Flux ◽  
High Brightness ◽  
Pulsar Radio ◽  
Pulsar Radiation ◽  
Amplification Process ◽  
Coherent Plasma ◽  
Pulsar Radio Emission

In this paper we present an account of a theory of pulsar radio emission. The emission mechanism is via a maser amplification process. This theory avoids the difficulty of coherent plasma emission, that the bandwidth of radiation must be less than 1/2 λ. The high brightness radio temperature and the insensitivity of pulsar radio flux to pulsar periods can be easily accounted for.

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