Low-Frequency Observations of Drifting, Non-Thermal Continuum Radio Emission Associated with the Solar Coronal Mass Ejections (original) (raw)
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Radio Observations of Coronal Mass Ejection Initiation and Development in the Low Solar Corona
Frontiers in Astronomy and Space Sciences, 2020
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.
The Astrophysical Journal, 2012
It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g., spectral bumps) of the dynamic spectra of type II radio bursts to imaging features (e.g., coronal mass ejection (CME) going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME-streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio-emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated electron acceleration by CME-driven shock.
The Astrophysical Journal
Understanding electron acceleration associated with magnetic energy release at subsecond scales presents major challenges in solar physics. Solar radio spikes observed as subsecond, narrow-bandwidth bursts with Δf/f ∼ 10−3–10−2 are indicative of a subsecond evolution of the electron distribution. We present a statistical analysis of frequency- and time-resolved imaging of individual spikes and Type IIIb striae associated with a coronal mass ejection (CME). LOFAR imaging reveals that the cotemporal (<2 s) spike and striae intensity contours almost completely overlap. On average, both burst types have a similar source size with a fast expansion at millisecond scales. The radio source centroid velocities are often superluminal and independent of frequency over 30–45 MHz. The CME perturbs the field geometry, leading to increased spike emission likely due to frequent magnetic reconnection. As the field restores itself toward the prior configuration, the observed sky-plane emission loc...
Formation of Radio Type II Bursts During a Multiple Coronal Mass Ejection Event
Solar Physics, 2017
We study the solar event on 27 September 2001 that consisted of three consecutive coronal mass ejections (CMEs) originating from the same active region, which were associated with several periods of radio type II burst emission at decameter–hectometer (DH) wavelengths. Our analysis shows that the first radio burst originated from a low-density environment, formed in the wake of the first, slow CME. The frequency-drift of the burst suggests a low-speed burst driver, or that the shock was not propagating along the large density gradient. There is also evidence of band-splitting within this emission lane. The origin of the first shock remains unclear, as several alternative scenarios exist. The second shock showed separate periods of enhanced radio emission. This shock could have originated from a CME bow shock, caused by the fast and accelerating second or third CME. However, a shock at CME flanks is also possible, as the density depletion caused by the three CMEs would have affected ...
Transients and Mass Ejections Observed in Radio Occultation Measurements of the Solar Corona
A wide variety of radio propagation and scattering phenomena observed when a radio source is occulted by the solar corona has formed the basis for probing the solar corona for over four decades. The purpose of this paper is to review the subject of transients — variations in the radio occultation measurements that appear different from those of the background solar wind. A major surprise in the study of transients has been the realization that they can represent the passage of coronal streamers in addition to the coronal mass ejections (CMES) observed in white-light coronagraphs. Although common radio occultation and white-light measurements of CMES have been few and incomplete, some general features of CMEs are emerging. Two regions of enhanced density and density fluctuations appear common to CMES. The first represents the compressed plasma ahead of the CME, and is present whether or not the CME is traveling fast enough to generate an interplanetary shock, while the second corresp...
Detailed Investigation of a Moving Solar Burst Type IV Radio Emission in on Broadband Frequency
International Letters of Chemistry, Physics and Astronomy, 2014
The moving type IV burst component of the solar radio region from 260-380 MHz observed using the CALLISTO spectrometer is discussed in detail. We used the Compound Astronomical Low Cost Low Frequency Spectrometer Transportable Observatory (CALLISTO) system connected to the Log Periodic Dipole Antenna (LPDA) at the National Space Centre, Selangor located (3.0833333°N 101.5333333°E) on 22nd February 2012. It is found that a strong burst that caused by extraordinary solar flares are due to magnetic reconnection effect potentially induced in the near-Earth magneto tail. From our observation the indication of signal potentially drives Coronal Mass Ejections (CMEs). We also compare our results with the Geostationary Operational Environmental Satellites (GOES) data. From our analysis, one possible reason behind the formation of this very complex long duration of this loop is the magnetic reconnection and disruption of the loops which is observed during flare maximum. The Active Region, AR ...
The Coronal Mass Ejection of 1998 April 20: Direct Imaging at Radio Wavelengths
The Astrophysical Journal, 2001
We observed the fast coronal mass ejection (CME) of 1998 April 20 with the radioheliograph at Nançay, France, between 164 and 432 MHz. Spectroscopic data were obtained between 40 and 800 MHz by the spectrometer at Tremsdorf, Germany, and between 20 kHz and 14 MHz with the WAVES instrument on board the Wind spacecraft. Energetic particle data were obtained from the Wind 3D Plasma and Energetic Particle experiment. The CME was observed in white light by the Large-Angle Spectrometric COronagraph experiment on board the Solar and Heliospheric Observatory spacecraft. For the first time, the expanding CME loops are imaged directly at radio wavelengths. We show that the radio-emitting CME loops are the result of nonthermal synchrotron emission from electrons with energies of ∼0.5-5 MeV interacting with magnetic fields of ∼0.1 to a few gauss. They appear nearly simultaneously with the onset of an associated type II radio burst, shock-accelerated type III radio bursts, and the initiation of a solar energetic particle event. We suggest possible sources of the energetic electrons responsible for this "radio CME" and point out diagnostic uses for synchrotron emission from CME loops.
Observations of coronal mass ejections (CMEs) at low frequency radio region on 15th April 2012
We have carried out a case study on Coronal Mass Ejections (CMEs) as a massive burst of solar wind and magnetic fields rising above the solar corona. During 15th April 2012, solar filament eruption was accompanied by intense CMEs. This explosion of CMEs observed by the Solar Dynamics Observatory with sunspot AR1458 is crackling with C-class solar flares. Solar flare type B3 and C2 were observed beginning 2241 UT and 0142 UT in the active region AR1458. In the present work, we focus in the range of the low frequency region from 150 MHz to 400 MHz. At preliminary stage, starting from 12.00 UT till 1.00 UT there is a strong signal which indicates a formation of burst. Type II burst originated from solar corona can be observed in the range of 150 MHz to 230 MHz. Instead of type II, a moving type IV and continuum type III burst can be detected at 150 MHz and lasting for 1 hours. This event is considered as second largest CMEs been detected since five (5) years. We can then conclude that currently, the Sun is in the phase of gradually increase to reach maximum 24th solar cycle. Coronal Mass Ejections (CMEs), solar corona, solar flare, type II, type III, type IV, solar cycle, sun. 96.60.ph, 96.60.P-, 96.60.Tf, 96.60.tg, 96.60.qe, 96.60.qe, 92.60.Vb
Radio Observations of Weak Energy Releases in the Solar Corona
The Astrophysical Journal, 2010
We report observations of weak, circularly polarized, structureless type III bursts from the solar corona in the absence of Hα/X-ray flares and other related activity, during the minimum between the sunspot cycles 23 and 24. The spectral information about the event obtained with the CALLISTO spectrograph at Mauritius revealed that the drift rate of the burst is ≈−30 MHz s −1 is in the range 50-120 MHz. Two-dimensional imaging observations of the burst at 77 MHz obtained with the Gauribidanur radioheliograph indicate that the emission region was located at a radial distance of ≈1.5 R in the solar atmosphere. The estimated peak brightness temperature of the burst at 77 MHz is ∼10 8 K. We derived the average magnetic field at the aforementioned location of the burst using the one-dimensional (east-west) Gauribidanur radio polarimeter at 77 MHz, and the value is ≈2.5 ± 0.2 G. We also estimated the total energy of the non-thermal electrons responsible for the observed burst as ≈1.1 × 10 24 erg. This is low compared to the energy of the weakest hard X-ray microflares reported in the literature, which is about ∼10 26 erg. The present result shows that non-thermal energy releases that correspond to the nanoflare category (energy ∼10 24 erg) are taking place in the solar corona, and the nature of such small-scale energy releases has not yet been explored.
Comparative analysis of solar radio bursts before and during CME propagation
Astronomy & Astrophysics
Context. As is well known, coronal mass ejection (CME) propagation often results in the fragmentation of the solar atmosphere on smaller regions of density (magnetic field) enhancement (depletion). It is expected that this type of fragmentation may have radio signatures. Aims. The general aim of the present paper is to perform a comparative analysis of type III solar and narrow-band type-III-like radio burst properties before and during CME events, respectively. The main goal is to analyze radio observational signatures of the dynamical processes in solar corona. In particular, we aim to perform a comparison of local plasma parameters without and with CME propagation, based on the analysis of decameter radio emission data. Methods. In order to examine this intuitive expectation, we performed a comparison of usual type III bursts before the CME with narrow-band type-III-like bursts, which are observationally detectable on top of the background type IV radio bursts associated with CME...