Browsing by Subject "BURSTS"

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  • Morosan, D. E.; Palmerio, E.; Räsänen, J. E.; Kilpua, E. K. J.; Magdalenic, J.; Lynch, B. J.; Kumari, A.; Pomoell, J.; Palmroth, M. (2020)
    Context. Coronal mass ejections (CMEs) are large eruptions of magnetised plasma from the Sun that are often accompanied by solar radio bursts produced by accelerated electrons.Aims. A powerful source for accelerating electron beams are CME-driven shocks, however, there are other mechanisms capable of accelerating electrons during a CME eruption. So far, studies have relied on the traditional classification of solar radio bursts into five groups (Type I-V) based mainly on their shapes and characteristics in dynamic spectra. Here, we aim to determine the origin of moving radio bursts associated with a CME that do not fit into the present classification of the solar radio emission.Methods. By using radio imaging from the Nancay Radioheliograph, combined with observations from the Solar Dynamics Observatory, Solar and Heliospheric Observatory, and Solar Terrestrial Relations Observatory spacecraft, we investigate the moving radio bursts accompanying two subsequent CMEs on 22 May 2013. We use three-dimensional reconstructions of the two associated CME eruptions to show the possible origin of the observed radio emission.Results. We identified three moving radio bursts at unusually high altitudes in the corona that are located at the northern CME flank and move outwards synchronously with the CME. The radio bursts correspond to fine-structured emission in dynamic spectra with durations of similar to 1 s, and they may show forward or reverse frequency drifts. Since the CME expands closely following an earlier CME, a low coronal CME-CME interaction is likely responsible for the observed radio emission.Conclusions. For the first time, we report the existence of new types of short duration bursts, which are signatures of electron beams accelerated at the CME flank. Two subsequent CMEs originating from the same region and propagating in similar directions provide a complex configuration of the ambient magnetic field and favourable conditions for the creation of collapsing magnetic traps. These traps are formed if a CME-driven wave, such as a shock wave, is likely to intersect surrounding magnetic field lines twice. Electrons will thus be further accelerated at the mirror points created at these intersections and eventually escape to produce bursts of plasma emission with forward and reverse drifts.
  • Morosan, D. E.; Palmerio, E.; Lynch, B. J.; Kilpua, E. K. J. (2020)
    Context. Coronal mass ejections (CMEs) on the Sun are the largest explosions in the Solar System that can drive powerful plasma shocks. The eruptions, shocks, and other processes associated to CMEs are efficient particle accelerators and the accelerated electrons in particular can produce radio bursts through the plasma emission mechanism. Aims. Coronal mass ejections and associated radio bursts have been well studied in cases where the CME originates close to the solar limb or within the frontside disc. Here, we study the radio emission associated with a CME eruption on the back side of the Sun on 22 July 2012. Methods. Using radio imaging from the Nancay Radioheliograph, spectroscopic data from the Nancay Decametric Array, and extreme-ultraviolet observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, we determine the nature of the observed radio emission as well as the location and propagation of the CME. Results. We show that the observed low-intensity radio emission corresponds to a type II radio burst or a short-duration type IV radio burst associated with a CME eruption due to breakout reconnection on the back side of the Sun, as suggested by the pre-eruptive magnetic field configuration. The radio emission consists of a large, extended structure, initially located ahead of the CME, that corresponds to various electron acceleration locations. Conclusions. The observations presented here are consistent with the breakout model of CME eruptions. The extended radio emission coincides with the location of the current sheet and quasi-separatrix boundary of the CME flux and the overlying helmet streamer and also with that of a large shock expected to form ahead of the CME in this configuration.
  • Carley, Eoin P.; Hayes, Laura A.; Murray, Sophie A.; Morosan, Diana E.; Shelley, Warren; Vilmer, Nicole; Gallagher, Peter T. (2019)
    Solar flares often involve the acceleration of particles to relativistic energies and the generation of high-intensity bursts of radio emission. In some cases, the radio bursts can show periodic or quasiperiodic intensity pulsations. However, precisely how these pulsations are generated is still subject to debate. Prominent theories employ mechanisms such as periodic magnetic reconnection, magnetohydrodynamic (MHD) oscillations, or some combination of both. Here we report on high-cadence (0.25 s) radio imaging of a 228 MHz radio source pulsating with a period of 2.3 s during a solar flare on 2014-April-18. The pulsating source is due to an MHD sausage mode oscillation periodically triggering electron acceleration in the corona. The periodic electron acceleration results in the modulation of a loss-cone instability, ultimately resulting in pulsating plasma emission. The results show that a complex combination of MHD oscillations and plasma instability modulation can lead to pulsating radio emission in astrophysical environments.
  • Morosan, Diana E.; Carley, Eoin P.; Hayes, Laura A.; Murray, Sophie A.; Zucca, Pietro; Fallows, Richard A.; McCauley, Joe; Kilpua, Emilia K. J.; Mann, Gottfried; Vocks, Christian; Gallagher, Peter T. (2019)
    The Sun is an active star that can launch large eruptions of magnetized plasma into the heliosphere, known as corona! mass ejections (CMEs). These can drive shocks that accelerate particles to high energies, often resulting in radio emission at low frequencies (
  • Ramesh, R.; Kumari, A.; Kathiravan, C.; Ketaki, D.; Wang, T. J. (2021)
    We report observations of thermal emission from the frontal structure of a coronal mass ejection (CME) using data obtained with the Gauribidanur RAdioheliograPH simultaneously at 80 and 53 MHz on May 1, 2016. The CME was due to activity on the far side of the Sun, but near its limb. No nonthermal radio burst activity was noticed. This provided an opportunity to observe the faint thermal radio emission from the CME, and hence directly estimate the electron density, mass, and magnetic field strength of the plasma entrained in the CME. Considering that CMEs are mostly observed only in whitelight and reports on their plasma characteristics are also limited, the rare direct radio observations of thermal emission from a CME and independent diagnosis of its plasma parameters are important measurements in the field of CME physics. Plain Language Summary Near-Sun observations of coronal mass ejections (CMEs) in white light are difficult with the existing coronagraphs due to the large size of their occulting disks. Furthermore the observations are limited to the corona off the solar limb since the occulting disks cover the corona overlying the solar disk. Radio observations are useful in this connection since there are no occulting disks. So both disk as well as limb corona can be simultaneously observed. Additionally, it is easier to carry out polarization studies and also calibrate the data using observations of other cosmic radio sources.
  • Dabrowski, B. P.; Morosan, D. E.; Fallows, R. A.; Blaszkiewicz, L.; Krankowski, A.; Magdalenic, J.; Vocks, C.; Mann, G.; Zucca, P.; Sidorowicz, T.; Hajduk, M.; Kotulak, K.; Fron, A.; Sniadkowska, K. (2018)
    We report first results of solar spectroscopic observations carried out with the Baldy LOFAR (LOw-Frequency ARray) station, Poland from October 2016 to July 2017. During this time, we observed different types of radio emission: type I and type III radio bursts. Our observations show that the station is fully operational and it is capable to work efficiently in the single station mode for solar observations. Furthermore, in this paper we will briefly describe the observational technique and instrument capabilities and show some examples of first observations. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved.
  • Morosan, D. E.; Palmerio, E.; Pomoell, J.; Vainio, R.; Palmroth, M.; Kilpua, E. K. J. (2020)
    Context. Some of the most prominent sources for particle acceleration in our Solar System are large eruptions of magnetised plasma from the Sun called coronal mass ejections (CMEs). These accelerated particles can generate radio emission through various mechanisms. Aims. CMEs are often accompanied by a variety of solar radio bursts with different shapes and characteristics in dynamic spectra. Radio bursts directly associated with CMEs often show movement in the direction of CME expansion. Here, we aim to determine the emission mechanism of multiple moving radio bursts that accompanied a flare and CME that took place on 14 June 2012. Methods. We used radio imaging from the Nancay Radioheliograph, combined with observations from the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory spacecraft, to analyse these moving radio bursts in order to determine their emission mechanism and three-dimensional (3D) location with respect to the expanding CME. Results. In using a 3D representation of the particle acceleration locations in relation to the overlying coronal magnetic field and the CME propagation, for the first time, we provide evidence that these moving radio bursts originate near the CME flanks and that some are possible signatures of shock-accelerated electrons following the fast CME expansion in the low corona. Conclusions. The moving radio bursts, as well as other stationary bursts observed during the eruption, occur simultaneously with a type IV continuum in dynamic spectra, which is not usually associated with emission at the CME flanks. Our results show that moving radio bursts that could traditionally be classified as moving type IVs can represent shock signatures associated with CME flanks or plasma emission inside the CME behind its flanks, which are closely related to the lateral expansion of the CME in the low corona. In addition, the acceleration of electrons generating this radio emission appears to be favoured at the CME flanks, where the CME encounters coronal streamers and open field regions.