Solar Type IIIb Radio Bursts as Tracers for Electron Density Fluctuations in the Corona

Mugundhan, V.; Hariharan, K.; Ramesh, R.

doi:10.1007/s11207-017-1181-5

Cited by 34 publications

(31 citation statements)

References 71 publications

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“…The small fluctuations seen in the spectra are noteworthy. Similar behaviour has been observed for type-IIIb solar bursts, and has been interpreted as arising due to the presence of density inhomogenities in the medium (Ellis 1969;de La Noe 1975;Loi et al 2014;Mugundhan et al 2017;Kontar et al 2017). In the radio images used for this study, the typical root mean square (rms) of the flux densities in a blank sky region far from the Sun is ≈ 0.015 SFU.…”

Section: Implications Of the Non-thermal Radio Emissionssupporting

confidence: 75%

A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

Mohan

McCauley

Oberoi

et al. 2019

ApJ

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Weak heating events are frequent and ubiquitous in solar corona. They derive their energy from the local magnetic field and form a major source of local heating, signatures of which are seen in EUV and X-ray bands. Their radio emission arise from various plasma instabilities that lead to coherent radiation, making even a weak flare appear very bright. The radio observations hence probe non-equilibrium dynamics providing complementary information on plasma evolution. However, a robust study of radio emission from a weak event among many simultaneous events, requires high dynamic range imaging at sub-second and sub-MHz resolutions owing to their high spectro-temporal variability. Such observations were not possible until recently. This is among the first spatially resolved studies of an active region loop hosting a transient brightening (ARTB) and dynamically linked to a metrewave type-I noise storm. It uses imaging observations at metrewave, EUV and X-ray bands, along with magnetogram data. We believe this is the first spectroscopic radio imaging study of a type-I source, the data for which was obtained using the Murchison Widefield Array. We report the discovery of 30 s quasi-periodic oscillations (QPOs) in the radio light curve, riding on a coherent baseline flux. The strength of the QPOs and the baseline flux enhanced during a mircoflare associated with the ARTB. Our observations suggest a scenario where magnetic stress builds up over an Alfvén timescale (30s) across the typical magnetic field braiding scale and then dissipates via a cascade of weak reconnection events.

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Section: Implications Of the Non-thermal Radio Emissionssupporting

confidence: 75%

A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

Mohan

McCauley

Oberoi

et al. 2019

ApJ

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“…2006a, 2012b; Kathiravan et al 2011;Mercier et al 2015;Mugundhan et al 2016Mugundhan et al , 2018. The fact that the Sun is presently in the phase of minimum activity, (during which the observations reported in the present work were carried out) also indicates that the scattering will be less (Sasikumar Raja et al 2016;Mugundhan et al 2017). We calculated N e at the above two heliocentric distances using the relation N e = fp 9×10 −3 2 , where f p is the fundamental plasma frequency in units of MHz, and N e is in units of cm −3 .…”

Section: Optical Observationsmentioning

confidence: 58%

Direct Estimates of the Solar Coronal Magnetic Field Using Contemporaneous Extreme-ultraviolet, Radio, and White-light Observations

Kumari

Ramesh

Kathiravan

et al. 2019

ApJ

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We report a solar coronal split-band type II radio burst that was observed on 2016 March 16 with the Gauribidanur Radio Spectro-Polarimeter (GRASP) in the frequency range ≈ 90 -50 MHz, and the Gauribidanur RadioheliograPH (GRAPH) at two discrete frequencies, viz. 80 MHz and 53.3 MHz. Observations around the same epoch in extreme-ultraviolet (EUV) and white-light show that the above burst was associated with a flux rope structure and a coronal mass ejection (CME), respectively. The combined height-time plot generated using EUV, radio, and whitelight data suggest that the different observed features (i.e. the flux rope, type II burst and the CME) are all closely associated. We constructed an empirical model for the coronal electron density distribution (N e (r), where r is the heliocentric distance) from the above set of observations themselves and used it to estimate the coronal magnetic field strength (B) over the range of r values in which the respective events were observed. The B values are consistent with each other. They vary as B(r) = 2.61×r −2.21 G in the range r ≈ 1.1 -2.2R . As far as we know, similar 'direct' estimates of B in the near-Sun corona without assuming a model for N e (r), and by combining co-temporal set of observations in two different regions (radio and whitelight) of the electromagnetic spectrum, have rarely been reported. Further, the present work is a novel attempt where the characteristics of a propagating EUV flux rope structure, considered to be the signature of a CME close the Sun, have been used to estimate B(r) in the corresponding distance range.

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“…The remaining 150 type III bursts were not associated with any flare. These 150 bursts were probably due to weak energy releases in the solar atmosphere reported earlier in the literature (for example, Ramesh et al (2010Ramesh et al ( , 2013; Saint-Hilaire, Vilmer, and Kerdraon (2013); Sasikumar Raja and Ramesh (2013b); Mugundhan, Hariharan, and Ramesh (2017); James, Subramanian, and Kontar (2017); James and Subramanian (2018); Sharma, Oberoi, and Arjunwadkar (2018)). We also find that 75% of the type III bursts in our list were observed below 200 MHz (left panel of Figure 5).…”

Section: Preliminary Analysis Of Type III Burstsmentioning

confidence: 79%

Automated Detection of Solar Radio Bursts Using a Statistical Method

et al. 2019

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Radio bursts from the solar corona can provide clues to forecast space weather hazards. After recent technology advancements, regular monitoring of radio bursts has increased and large observational data sets are produced. Hence, manual identification and classification of them is a challenging task. In this paper, we describe an algorithm to automatically identify radio bursts from dynamic solar radio spectrograms using a novel statistical method. We used e-CALLISTO radio spectrometer data observed at Gauribidanur observatory near Bangalore in India during 2013 -2014. We have studied the classifier performance using the receiver operating characteristics. Further, we studied type III bursts observed in the year 2014 and found that 75% of the observed bursts were below 200 MHz. Our analysis shows that the positions of the flare sites which are associated with the type III bursts with upper frequency cut-off 200 MHz

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Solar Type IIIb Radio Bursts as Tracers for Electron Density Fluctuations in the Corona

Cited by 34 publications

References 71 publications

A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

Direct Estimates of the Solar Coronal Magnetic Field Using Contemporaneous Extreme-ultraviolet, Radio, and White-light Observations

Automated Detection of Solar Radio Bursts Using a Statistical Method

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