A Solar Stationary Type IV Radio Burst and Its Radiation Mechanism

Liu, Hongyu; Chen, Yao; Cho, Kyung-Suk; Feng, Shiwei; Vasanth, V.; Koval, A. A.; Du, Guojun; Wu, Zhao; Li, Chuanyang

doi:10.1007/s11207-018-1280-y

Cited by 22 publications

(16 citation statements)

References 37 publications

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“…Several others have examined source positions and structures in total intensity NRH observations, while using the polarization information to help discriminate between emission mechanisms (e.g. Gopalswamy et al, 1994;Tun and Vourlidas, 2013;Kong et al, 2016;Liu et al, 2018). The radioheliograph at Gauribidanur does not have a polarimetric capability itself, but several one-dimensional polarimeters have been installed alongside it (Ramesh et al, 2008;Kishore et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

The Low-Frequency Solar Corona in Circular Polarization

et al. 2019

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We present spectropolarimetric imaging observations of the solar corona at low frequencies (80 -240 MHz) using the Murchison Widefield Array (MWA). These images are the first of their kind, and we introduce an algorithm to mitigate an instrumental artefact by which the total intensity signal contaminates the polarimetric images due to calibration errors. We then survey the range of circular polarization (Stokes V ) features detected in over 100 observing runs near solar maximum during quiescent periods. First, we detect around 700 compact polarized sources across our dataset with polarization fractions ranging from less than 0.5 % to nearly 100 %. These sources exhibit a positive correlation between polarization fraction and total intensity, and we interpret them as a continuum of plasma emission noise storm (Type I burst) continua sources associated with active regions. Second, we report a characteristic "bullseye" structure observed for many low-latitude coronal holes in which a central polarized component is surrounded by a ring of the opposite sense. The central component does not match the sign expected from thermal bremsstrahlung emission, and we speculate that propagation effects or an alternative emission mechanism may be responsible. Third, we show that the large-scale polarimetric structure at our lowest frequencies is reasonably well-correlated with the line-of-sight (LOS) magnetic field component inferred from a global potential field source surface (PFSS) model. The boundaries between opposite circular polarization signs are generally aligned with polarity inversion lines in the model at a height roughly corresponding to that of the radio limb. This is not true at our highest frequencies, however, where the LOS magnetic field direction and polarization sign are often not straightforwardly correlated.

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Section: Introductionmentioning

confidence: 99%

The Low-Frequency Solar Corona in Circular Polarization

et al. 2019

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“…The likely ECM driven type IV bursts are also broadband and highly circularly polarized. However, this kind of burst is often longer in duration (> 10 minutes) (Liu et al, 2018), although this duration difference could possibly be accounted for by a difference in beaming geometry between EQ Peg and the Sun should ECM be the responsible process. It is also possible that the flare lasted longer, but we were only able to detect it during the time it was brightest.…”

Section: Discussionmentioning

confidence: 99%

Observing flare stars below 100 MHz with the LWA

Davis

Taylor

Dowell

2020

Monthly Notices of the Royal Astronomical Society

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We observed the flare stars AD Leonis, Wolf 424, EQ Pegasi, EV Lacertae, and UV Ceti for nearly 135 hours. These stars were observed between 63 and 83 MHz using the interferometry mode of the Long Wavelength Array. Given that emission from flare stars is typically circularly polarized, we used the condition that any significant detection present in Stokes I must also be present in Stokes V at the same time in order for us to consider it a possible flare. Following this, we made one marginal flare detection for the star EQ Pegasi. This flare had a flux density of 5.91 Jy in Stokes I and 5.13 Jy in Stokes V, corresponding to a brightness temperature 1.75 × 10 16 (r/r * ) −2 K.

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“…Boischot (1958) and Boischot and Daigne (1968) proposed that this emission is due to synchrotron radiation of 2.5-3 MeV electrons trapped in moving coronal magnetic structures with field strength on the order of 1 G. However, observations during this era also revealed the existence of similar broadband post-flare emissions without any systematic motions of the radio source (Pick-Gutmann, 1961). Type IV bursts have thus been subcategorized over the years into stationary and moving (see historical overviews from Robinson and Stewart (1985), Pick (1986), and Pick and Vilmer (2008)), with the moving component now attributed to energetic electrons trapped in the CME, emitting plasma emission (Duncan, 1980;Gary et al, 1985), gyrosynchrotron or synchrotron (Dulk and Altschuler, 1971;Bain et al, 2014;Carley et al, 2017), or sometimes electron cyclotron maser emission (Liu et al, 2018;Morosan et al, 2019a). If the emission mechanism can be readily identified, type IV bursts can therefore provide diagnostics of electron density, characteristics of the electron energy distribution (e.g., spectral index and maximum energy), or magnetic field strength in the CME flux rope.…”

Section: Type IV Radio Burstsmentioning

confidence: 99%

Radio Observations of Coronal Mass Ejection Initiation and Development in the Low Solar Corona

Carley

Vilmer

Vourlidas

2020

Front. Astron. Space Sci.

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Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the low solar corona into the heliosphere. These eruptions are often associated with energetic electrons that produce various kinds of radio emission. However, there is ongoing investigation into exactly where, when, and how the electron acceleration occurs during flaring and eruption, and how the associated radio emission can be exploited as a diagnostic of both particle acceleration and CME eruptive physics. Here, we review past and present developments in radio observations of flaring and eruption, from the destabilization of flux ropes to the development of a CME and the eventual driving of shocks in the corona. We concentrate primarily on the progress made in CME radio physics in the past two decades and show how radio imaging spectroscopy provides the ability to diagnose the locations and kinds of electron acceleration during eruption, which provides insight into CME eruptive models in the early stages of their evolution ( < 10 R ⊙ ). We finally discuss how new instrumentation in the radio domain will pave the way for a deeper understanding of CME physics in the near future.

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A Solar Stationary Type IV Radio Burst and Its Radiation Mechanism

Cited by 22 publications

References 37 publications

The Low-Frequency Solar Corona in Circular Polarization

The Low-Frequency Solar Corona in Circular Polarization

Observing flare stars below 100 MHz with the LWA

Radio Observations of Coronal Mass Ejection Initiation and Development in the Low Solar Corona

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