Multiwavelength observations of a metric type-II event

Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.; Hillaris, A.

doi:10.1051/0004-6361/202141672

Cited by 9 publications

(4 citation statements)

References 96 publications

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“…All five frequencies are within the spectral range of the ASG, while the last three are also within the range of the SAO. The 2D NRH images from the Nançay site (https://rsdb.obs-nancay.fr/ (accessed on 23 July 2023)) supplement the ARTEMIS-IV/JLS dynamic spectra by providing information on the position and on the morphological evolution of the radio features on the solar disk (See for example [35][36][37][38]). Furthermore, the imaging information contributes to the determination of the nature of the emission.…”

Section: Observations and Data Analysis 21 Instrumentationmentioning

confidence: 99%

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

Alissandrakis,

Hillaris,

Bouratzis

et al. 2023

Universe

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Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of spectral radio data with high time and high frequency resolution has provided a wealth of information on phenomena of short duration and narrow bandwidth. Of particular value are spectral data combined with imaging observations at specific frequencies. In this work we briefly review the results of a series of observations comprised from high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-IV/JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay Radioheliograph (NRH). Our studies include fine structures embedded in type-IV burst continua (mostly narrow-band “spikes” and intermediate drift “fiber” bursts) and spike-like structures detected near the front of type-II bursts. The implications of the observational results to theoretical models are discussed.

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Section: Observations and Data Analysis 21 Instrumentationmentioning

confidence: 99%

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

Alissandrakis,

Hillaris,

Bouratzis

et al. 2023

Universe

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“…Type II solar radio bursts are produced by magnetohydrodynamic (MHD) shocks driven by solar eruptive events such as coronal mass ejections (CMEs), flares, and jets (Nelson & Melrose 1985;Nindos et al 2011;Gopalswamy et al 2018;Zucca et al 2018;Maguire et al 2021;Jebaraj et al 2021;Alissandrakis et al 2021). The shock waves accelerate electrons, producing Langmuir waves and subsequently plasma emissions at the fundamental ( f p ) and second harmonic (2 f p ) of the plasma frequency, given by f p ≈ 8980…”

Section: Introductionmentioning

confidence: 99%

Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array

Bhunia

Carley

Oberoi

et al. 2023

A&A

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Type II solar radio bursts are caused by magnetohydrodynamic (MHD) shocks driven by solar eruptive events such as coronal mass ejections (CMEs). Often, both fundamental and harmonic bands of type II bursts are split into sub-bands, which are generally believed to be coming from upstream and downstream regions of the shock; however, this explanation remains unconfirmed. Here, we present combined results from imaging analyses of type II radio burst band splitting and other fine structures observed by the Murchison Widefield Array (MWA) and extreme ultraviolet observations from Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) on 28 September 2014. The MWA provides imaging-spectroscopy in the range 80−300 MHz with a time resolution of 0.5 s and frequency resolution of 40 kHz. Our analysis shows that the burst was caused by a piston-driven shock with a driver speed of ∼112 km s−1 and shock speed of ∼580 km s−1. We provide rare evidence that band splitting is caused by emission from multiple parts of the shock (as opposed to the upstream–downstream hypothesis). We also examine the small-scale motion of type II fine structure radio sources in MWA images, and suggest that this motion may arise because of radio propagation effects from coronal turbulence, and is not due to the physical motion of the shock location. We present a novel technique that uses imaging spectroscopy to directly determine the effective length scale of turbulent density perturbations, which is found to be 1−2 Mm. The study of the systematic and small-scale motion of fine structures may therefore provide a measure of turbulence in different regions of the shock and corona.

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“…Polarization of the harmonic plasma emission is also minimally affected by propagation effects (Dulk & McLean 1978). Observations of circular polarization of type II radio bursts are known since the time the bursts were discovered (Komesaroff 1958;Roberts 1959;Stewart 1966;Suzuki et al 1980;Cairns & Robinson 1987;Thejappa et al 2003;Du et al 2014;Alissandrakis et al 2021). There are also estimates of B using observations of weak circular polarized emission from harmonic type II bursts (Hariharan et al 2014;Kumari et al 2017aKumari et al , 2019Ramesh & Kathiravan 2022b).…”

Section: Introductionmentioning

confidence: 99%

Polarization Observations of a Split-band Type II Radio Burst from the Solar Corona

Ramesh

Kathiravan

2022

ApJ

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Using temporal observations of circular polarized harmonic plasma emission from a split-band type II solar radio burst at 80 MHz, we separately estimated the coronal magnetic field strengths (B) associated with the lower (L) and upper (U) frequency bands of the burst. The corresponding Stokes I and V data were obtained with the polarimeter operating at the above frequency in the Gauribidanur observatory. The burst was associated with a flare/coronal mass ejection on the solar disk. Simultaneous spectral observations with the spectrograph there in the frequency range 80–35 MHz helped to establish that the observed polarized emission was from the harmonic component of the burst. The B values corresponding to the polarized emission from the L and U bands at 80 MHz are B L ≈ 1.2 G and B U ≈ 2.4 G, respectively. The different values of B for the observed harmonic emission at the same frequency (80 MHz) from the two bands imply unambiguously that the corresponding fundamental emission at 40 MHz must have originated at different spatial locations. Two-dimensional radio imaging observations of the burst with the radioheliograph in the same observatory at 80 MHz indicate the same. As comparatively higher B is expected behind a propagating shock due to compression as well as the corresponding coronal regions being closer to the Sun, our results indicate that the sources of L- and U-band emission should be located ahead of and behind the associated coronal shock, respectively. These are useful to understand the pre- and postshock corona as well as locations of electron acceleration in a propagating shock.

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Multiwavelength observations of a metric type-II event

Cited by 9 publications

References 96 publications

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array

Polarization Observations of a Split-band Type II Radio Burst from the Solar Corona

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