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.

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 Evolution of Unstable 'Beta-Gamma' Magnetic Fields of Active Region AR 2222

2015 ◽  
Vol 48 ◽  
pp. 95-102
Author(s):  
Zety Sharizat Hamidi ◽  
S.N.U. Sabri ◽  
N.N.M. Shariff ◽  
C. Monstein
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Solar Flares ◽  
Active Regions ◽  
Group Type ◽  
Solar Burst ◽  
Type Iv ◽  
Fine Structures ◽  
Using Data

This event allows us to investigate how plasma–magnetic field interactions in the solar corona can produce suprathermal electron populations over periods from tens of minutes to several hours, and the interactions of wave-particle and wave-wave lead to characteristic fine structures of the emission. An intense and broad solar radio burst type IV was recorded by CALLISTO spectrometer from 240-360 MHz. Using data from a the KRIM observatory, we aim to provide a comprehensive description of the synopsis formation and dynamics of a a single solar burst type IV event due to active region AR2222. For five minutes, the event exhibited strong pulsations on various time scales and “broad patterns” with a formation of a group type III solar burst. AR 2222 remained the most active region, producing a number of minor C-Class solar flares. The speed of the solar wind also exceeds 370.8 km/second with 10.2 g/cm3 density of proton in the solar corona. The radio flux also shows 171 SFU. Besides, there are 3 active regions, AR2217, AR2219 and AR2222 potentially pose a threat for M-class solar flares. Active region AR2222 have unstable 'beta-gamma' magnetic fields that harbor energy for M-class flares. As a conclusion, we believed that Sun’s activities more active in order to achieve solar maximum cycle at the end of 2014.

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.

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.

scholarly journals The Gyro-Synchrotron Radiation from Moving Type IV Sources in the Solar Corona

1974 ◽  
Vol 57 ◽  
pp. 481-482
Author(s):  
G. A. Dulk
Keyword(s):  
Solar Corona ◽  
Circular Polarization ◽  
The Self ◽  
Synchrotron Emission ◽  
Turnover Frequency ◽  
Moving Sources ◽  
Type Iv ◽  
Inhomogeneous Sphere ◽  
High Degree ◽  
Lower Frequencies

(Solar Phys.). Calculations of the gyro-synchrotron emission are made for conditions which might be expected in moving type IV sources in the solar corona. Two simple models for an evolving source are treated: a uniform cube and an inhomogeneous sphere. The results suggest that most moving sources have the following features: (1) A rather strong magnetic field, ≈ 10 G, is carried out within the source. This is required to achieve the high degree of circular polarization often observed. (2) Synchrotron self-absorption causes the source to be optically thick at frequencies less than about 100 MHz, thus restricting the bandwidth of the radiation. The self-absorption decreases as the source moves outward and expands. The turnover frequency, which separates the optically thick and thin spectral regimes, moves rapidly to lower frequencies, accompanied by a change from low to high circular polarization. In the case of an inhomogeneous source, the source appears to be larger at the lower frequencies. (3) Razin-Tsytovich suppression cannot be an important factor in determining the characteristics of most sources.

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