On the Polarization and Rapid Fade-out of Moving Type IV Solar Bursts

1970 ◽  
Vol 1 (8) ◽  
pp. 372-374 ◽  
Author(s):  
G. A. Dulk
Keyword(s):  
Synchrotron Radiation ◽  
Circular Polarization ◽  
Source Region ◽  
Relativistic Electrons ◽  
Constant Intensity ◽  
Precise Position ◽  
Polarization Measurements ◽  
Type Iv ◽  
Solar Bursts

Since the advent of the 80 MHz radioheliograph, precise position and polarization measurements have become available on several moving type IV bursts. Two of the more puzzling characteristics of these bursts are : (1) they exhibit strong circular polarization in parts or all of the source region ; (2) after moving outward to as much as 3 R⊙ with relatively constant intensity, they rapidly fade away. In this paper we discuss the polarization and intensity of synchrotron radiation from mildly relativistic electrons and suggest betatron deceleration as a mechanism to explain the rapid fade-out of the moving type IV sources. The results are applied to two examples of moving type IV bursts.

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.

Observation of Strong Circular Polarization in a Moving Type IV Burst

1969 ◽  
Vol 1 (5) ◽  
pp. 189-191 ◽  
Author(s):  
K. Kai
Keyword(s):  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Circular Polarization ◽  
Type Iv ◽  
Weak Magnetic Fields

Since they were first interpreted, moving type IV bursts have been attributed to synchrotron radiation from electrons with energy ∼3 MeV radiating in weak magnetic fields (∼1 G) high in the solar corona. In this paper a description is given of 80 MHz radioheliograph observations of an outburst in which it was possible to isolate the moving type IV source and demonstrate that its circular polarization was strong (∼80%). Hence it is shown that the energy of the radiating electrons cannot exceed 6 = 105eV.

Radio Emission from Starspots on RSCVn Binary HR1099

1986 ◽  
Vol 6 (3) ◽  
pp. 316-319 ◽  
Author(s):  
John D. Bunton ◽  
R. T. Stewart ◽  
O. B. Slee ◽  
G. J. Nelson ◽  
Alan E. Wright ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Light Curve ◽  
Circular Polarization ◽  
Rotation Rate ◽  
Source Model ◽  
Microwave Emission ◽  
Relativistic Electrons ◽  
Synchrotron Source

AbstractProperties of the microwave emission from HR1099 are examined in an attempt to determine whether the emission arises as gyro-synchrotron radiation from mildly relativistic electrons trapped in magnetic fields above starspots on the active K subgiant component. It is shown that radio curves do not exhibit a systematic variation in phase with the rotation rate, as one might expect for emission from a source situated above a long-lived starspot. However, there is some evidence that the radio flaring occurs at two preferred longitude zones. Whether these zones agree with starspot locations remains to be determined by light curve modelling. What we can say with confidence is that the measured spectral index of the microwave emission does not fit a simple gyro-synchrotron source model, such as that proposed to explain the observed reversal with frequency of the sense of circular polarization.

scholarly journals 80 MHz Radioheliograph Evidence on Moving Type IV Bursts and Coronal Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 616-641 ◽  
Author(s):  
S. F. Smerd ◽  
G. A. Dulk
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Magnetized Plasma ◽  
Relativistic Electrons ◽  
Radiation Mechanism ◽  
Type Iv ◽  
Coronal Magnetic Fields ◽  
Field Lines ◽  
Magnetic Arch

The characteristics of 12 moving type IV bursts observed with the 80 MHz radioheliograph at the Culgoora Observatory between February 1968 and April 1970 are summarized.Three classes of moving sources can be recognized; they are described as: (1) Expanding arch; (2) Advancing front; (3) Isolated source.The first class has been identified (Wild, 1969) with the expansion of a magnetic arch or loop; the second class is here identified with an advancing MHD disturbance which may accelerate the radiating electrons in situ when moving at greater than Alfvén speed; the third with solar ejecta in the form of magnetized plasma clouds, or plasmoids. In all cases the radiation mechanism is probably synchrotron radiation from mildly relativistic electrons; energies in the range ∼0.1 to ∼1 MeV could account for the observed strong circular polarizations.With an expanding magnetic arch, source and magnetic-field movement are inseparable; the field remains a closed loop throughout the event. The MHD front probably moves largely along and the plasmoids between the open magnetic-field lines of unipolar regions or helmet structures. In the latter case it is the internal magnetic field – possibly toroidal – of the moving plasmoid that determines the polarization of the synchrotron radiation. A preliminary comparison of moving type IV sources with Newkirk-Altschuler maps of coronal magnetic fields shows suitably located closed loops for 2 events identified as expanding magnetic arches and unipolar open field lines along the path of a moving source identified as a plasmoid.

A Model of the Evolution of the Flux Density and Polarization in Isolated Moving Type IV Bursts

1972 ◽  
Vol 2 (2) ◽  
pp. 95-98 ◽  
Author(s):  
E. J. Schmahl
Keyword(s):  
Synchrotron Radiation ◽  
Flux Density ◽  
Relativistic Electrons ◽  
Type Iv

In the first four years of operation with the 80 MHz heliograph at Culgoora, 24 events classified as moving type IV were observed. Their observed characteristics can be interpreted in terms of gyro-synchrotron radiation from mildly relativistic electrons. Many of these events have been presented at previous ASA meetings and 12 have been discussed in the literature in detail.

scholarly journals Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

2013 ◽  
Vol 31 (11) ◽  
pp. 2097-2121 ◽  
Author(s):  
P. M. E. Décréau ◽  
S. Kougblénou ◽  
G. Lointier ◽  
J.-L. Rauch ◽  
J.-G. Trotignon ◽  
...  
Keyword(s):  
Electric Field ◽  
Circular Polarization ◽  
Source Region ◽  
Plane Waves ◽  
Geomagnetic Latitude ◽  
Magnetic Activity ◽  
Spectral Signature ◽  
Time Interval ◽  
Field Polarization ◽  
Electric Field Polarization

Abstract. The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (~50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ~46°. This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (~1 RE). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15–25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ~ 10) and a medium geomagnetic latitude (35° S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

Evidence for Negative Deflection Angles inAr40+ Ag Deep-Inelastic Reactions fromγ-Ray Circular Polarization Measurements

1977 ◽  
Vol 39 (17) ◽  
pp. 1062-1065 ◽  
Author(s):  
W. Trautmann ◽  
J. de Boer ◽  
W. Dünnweber ◽  
G. Graw ◽  
R. Kopp ◽  
...  
Keyword(s):  
Circular Polarization ◽  
Negative Deflection ◽  
Polarization Measurements ◽  
Deep Inelastic Reactions

Synchrotron radiation from single electrons gyrating in a magnetoactive plasma

1969 ◽  
Vol 47 (7) ◽  
pp. 757-768 ◽  
Author(s):  
P. C. W. Fung
Keyword(s):  
Synchrotron Radiation ◽  
Plasma Frequency ◽  
Radiation Power ◽  
Magnetoactive Plasma ◽  
Electron Plasma ◽  
Relativistic Electrons ◽  
Relative Importance ◽  
Numerical Examples ◽  
The Past ◽  
Single Electrons

In this paper, the incoherent synchrotron radiation power emitted by relativistic electrons gyrating in a cold magnetoactive plasma is rederived, correcting errors which have occurred in the past literature. One can specify the background plasma by the quantity A = ωp2/ωH2 (ωp is the angular electron plasma frequency and ωH is the angular electron gyro-frequency), i.e. the relative importance of the plasma frequency to the gyro-frequency. The general spectral features of synchrotron radiation from single electrons radiating in plasmas of large [Formula: see text] and small [Formula: see text] are discussed with the aid of a number of numerical examples.

scholarly journals Complementary Bursts, Coronal Inhomogeneities and New Microscopic Spectral Features of Solar Bursts in Type IV Bursts

1980 ◽  
Vol 86 ◽  
pp. 269-271
Author(s):  
H. S. Sawant ◽  
R. V. Bhonsle ◽  
S. S. Degaonkar ◽  
T. Takakura
Keyword(s):  
High Frequency ◽  
High Sensitivity ◽  
Line Of Sight ◽  
Spectral Features ◽  
Frequency Range ◽  
Type Iv ◽  
Linear Extent ◽  
Solar Bursts ◽  
Almost All ◽  
Density Irregularity

Complementary bursts (C.B's) have been observed in the decametric range during noise storms and/or type IV activity. These bursts essentially consist of two components, each component having a duration ~ 1 second. The first component shows weak emission or emission gap over a certain frequency range. The second component is observed after a certain delay. If the bursts are assumed to be generated at the fundamental, and if the radiation corresponding to the gap propagates through an electron density irregularity located close to the source along the line of sight, whose cross-section is less than the linear extent of the source, then almost all properties of the C.B.'s can be explained. High sensitivity, and high frequency and time resolution spectra of type IV bursts at 137 MHz revealed new microscopic spectral features displaying “wave-like” and “fork-like” shapes.

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