scholarly journals Variable emission mechanism of a Type IV radio burst

2019 ◽  
Vol 623 ◽  
pp. A63 ◽  
Author(s):  
D. E. Morosan ◽  
E. K. J. Kilpua ◽  
E. P. Carley ◽  
C. Monstein
Keyword(s):  
Frequency Band ◽  
Radio Burst ◽  
Extreme Ultraviolet ◽  
Imaging Spectroscopy ◽  
Continuum Emission ◽  
Particle Accelerators ◽  
Radio Bursts ◽  
Emission Mechanism ◽  
Type Iv ◽  
Dynamic Spectra

Context. The Sun is an active star and the source of the largest explosions in the solar system, such as flares and coronal mass ejections (CMEs). Flares and CMEs are powerful particle accelerators that can generate radio emission through various emission mechanisms. Aims. CMEs are often accompanied by Type IV radio bursts that are observed as continuum emission in dynamic spectra at decimetric and metric wavelengths, but their emission mechanism can vary from event to event. Here, we aim to determine the emission mechanism of a complex Type IV burst that accompanied the flare and CME on 22 September 2011. Methods. We used radio imaging from the Nançay Radioheliograph, spectroscopic data from the e-Callisto network, ARTEMIS, Ondrejov, and Phoenix3 spectrometers combined with extreme-ultraviolet observations from NASA’s Solar Dynamic Observatory to analyse the Type IV radio burst and determine its emission mechanism. Results. We show that the emission mechanism of the Type IV radio burst changes over time. We identified two components in the Type IV radio burst: an earlier stationary Type IV showing gyro-synchrotron behaviour, and a later moving Type IV burst covering the same frequency band. This second component has a coherent emission mechanism. Fundamental plasma emission and the electron-cyclotron maser emission are further investigated as possible emission mechanisms for the generation of the moving Type IV burst. Conclusions. Type IV bursts are therefore complex radio bursts, where multiple emission mechanisms can contribute to the generation of the wide-band continuum observed in dynamic spectra. Imaging spectroscopy over a wide frequency band is necessary to determine the emission mechanisms of Type IV bursts that are observed in dynamic spectra.

Propagation of a Solar Moving Type IV Radio Burst Using LOFAR

2020 ◽  
Author(s):  
Hongyu Liu ◽  
Pietro Zucca ◽  
Jasmina Magdalenic ◽  
Peijin Zhang ◽  
Kyungsuk Cho
Keyword(s):  
Radio Burst ◽  
Wave Length ◽  
Detailed Comparison ◽  
Continuum Emission ◽  
Radio Bursts ◽  
High Brightness ◽  
Type Iv ◽  
Dynamic Spectra ◽  
Fine Structures ◽  
The Continuum

<p>Type IV radio burst is the long-lasting broadband continuum emission in metric wave-length. In addition to the continuum emission Type IV radio bursts may show fine structure with high brightness temperature. The physical emission responsible for both continuum and fine structures is still under debate. In this study, we present a moving type IV radio burst observed by LOFAR. We performed a detailed comparison of NRH and LOFAR imaging. Using the full stokes parameterss from the LOFAR dynamic spectra, we have also calculated the degree of circular polarisation during the propagation of the moving type IV. Finally, we combined LOFAR interferometric data with SDO-AIA and LASCO-C2 to track the evolution of this type IV and relate it with the CME.</p>

scholarly journals High-resolution observations with ARTEMIS-JLS and the NRH

2019 ◽  
Vol 627 ◽  
pp. A133 ◽  
Author(s):  
C. E. Alissandrakis ◽  
C. Bouratzis ◽  
A. Hillaris
Keyword(s):  
Large Scale ◽  
Extreme Ultraviolet ◽  
Flux Rope ◽  
Low Noise ◽  
Continuum Emission ◽  
High Time Resolution ◽  
Flare Loop ◽  
Type Iv ◽  
Dynamic Spectra ◽  
The Continuum

Aims. We study the characteristics of intermediate drift bursts (fibers) embedded in a large type-IV event. Methods. We used high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay radioheliograph (NRH) and extreme ultraviolet (EUV) images from the Transition Region and Coronal Explorer (TRACE) to study fiber bursts during the large solar event of July 14, 2000. We computed both 2D and 1D images and applied high pass time filtering to the images and the dynamic spectrum in order to enhance the fiber-associated emission. For the study of the background continuum emission we used images averaged over several seconds. Results. Practically all fibers visible in the SAO dynamic spectra are identifiable in the NRH images. Fibers were first detected after the primary energy release in a moving type-IV event, probably associated with the rapid eastward expansion of the flare and the post-flare loop arcade. We found that fibers appeared as a modulation of the continuum intensity with a root mean square value of the order of 10%. Both the fibers and the continuum were strongly circularly polarized in the ordinary mode sense, indicating plasma emission at the fundamental. We detected a number of discrete fiber emission sources along two parallel stripes of ∼300 Mm in length, apparently segments of large-scale loops encompassing both the EUV loops and the CME-associated flux rope. We found cases of multiple fiber emissions appearing at slightly different positions and times; their consecutive appearance can give the impression of apparent motion with supra-luminal velocities. Images of individual fibers were very similar at 432.0 and 327.0 MHz. From the position shift of the sources and the time delays at low and high frequencies, we estimated the exciter speed and the frequency scale length along the loops for a well-observed group of fibers; we obtained consistent values from imaging and spectral data, supporting the whistler origin of the fiber emission. Finally we found that fibers in emission and fibers in absorption are very similar, confirming that they are manifestations of the same wave train.

scholarly journals Three-dimensional reconstruction of multiple particle acceleration regions during a coronal mass ejection

2020 ◽  
Vol 635 ◽  
pp. A62 ◽  
Author(s):  
D. E. Morosan ◽  
E. Palmerio ◽  
J. Pomoell ◽  
R. Vainio ◽  
M. Palmroth ◽  
...  
Keyword(s):  
Particle Acceleration ◽  
Radio Emission ◽  
Three Dimensional ◽  
Coronal Magnetic Field ◽  
Radio Bursts ◽  
Emission Mechanism ◽  
Solar Dynamics Observatory ◽  
Type Iv ◽  
Dynamic Spectra ◽  
Solar Dynamics

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 Nançay 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.

scholarly journals Extended radio emission associated with a breakout eruption from the back side of the Sun

2020 ◽  
Vol 633 ◽  
pp. A141 ◽  
Author(s):  
D. E. Morosan ◽  
E. Palmerio ◽  
B. J. Lynch ◽  
E. K. J. Kilpua
Keyword(s):  
Radio Emission ◽  
Radio Burst ◽  
Coronal Mass Ejections ◽  
Extreme Ultraviolet ◽  
Particle Accelerators ◽  
Back Side ◽  
The Sun ◽  
Radio Bursts ◽  
Solar Dynamics Observatory ◽  
Extended Radio

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 Nançay Radioheliograph, spectroscopic data from the Nançay 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.

Using supervised machine learning to automatically detect type II and III solar radio bursts

2020 ◽  
Author(s):  
Eoin Carley
Keyword(s):  
Machine Learning ◽  
Radio Burst ◽  
Solar Radio ◽  
Machine Learning Algorithms ◽  
Supervised Machine Learning ◽  
Radio Bursts ◽  
Type Ii ◽  
Solar Radio Bursts ◽  
Dynamic Spectra

<p>Solar flares are often associated with high-intensity radio emission known as `solar radio bursts' (SRBs). SRBs are generally observed in dynamic spectra and have five major spectral classes, labelled type I to type V depending on their shape and extent in frequency and time. Due to their morphological complexity, a challenge in solar radio physics is the automatic detection and classification of such radio bursts. Classification of SRBs has become necessary in recent years due to large data rates (3 Gb/s) generated by advanced radio telescopes such as the Low Frequency Array (LOFAR). Here we test the ability of several supervised machine learning algorithms to automatically classify type II and type III solar radio bursts. We test the detection accuracy of support vector machines (SVM), random forest (RF), as well as an implementation of transfer learning of the Inception and YOLO convolutional neural networks (CNNs). The training data was assembled from type II and III bursts observed by the Radio Solar Telescope Network (RSTN) from 1996 to 2018, supplemented by type II and III radio burst simulations. The CNNs were the best performers, often exceeding >90% accuracy on the validation set, with YOLO having the ability to perform radio burst burst localisation in dynamic spectra. This shows that machine learning algorithms (in particular CNNs) are capable of SRB classification, and we conclude by discussing future plans for the implementation of a CNN in the LOFAR for Space Weather (LOFAR4SW) data-stream pipelines.</p>

scholarly journals The Coronal Disturbance of 12 August 1972

1974 ◽  
Vol 57 ◽  
pp. 335-336
Author(s):  
Anthony C. Riddle ◽  
Einar Tandberg-Hanssen ◽  
Richard T. Hansen
Keyword(s):  
High Altitude ◽  
Solar Phys ◽  
Radio Burst ◽  
Observational Evidence ◽  
Radio Bursts ◽  
Type Iv ◽  
Physical Picture ◽  
Complete Sequences ◽  
Coronal Structures

(Solar Phys.). The association of flare sprays, distortions of the overlying coronal structures and moving type IV radio bursts is a reasonable one and is well accepted despite the paucity of observational evidence. On 12 August 1972 there occurred a flare spray observed optically by both flare patrol (National Oceanographic and Atmospheric Administration) and coronagraph (High Altitude Observatory) instruments. A subsequent moving type IV radio burst was recorded on two swept frequency interferometers (Universities of Colorado and Maryland). In addition distinct changes in the K-coronal brightness at 1.6 R⊙ were measured (High Altitude Observatory K coronameter). These observations combine to form one of the most complete sequences of measurements yet recorded covering the range from the chromosphere to about 6 R⊙. The separate measurements are discussed and we show that they can be combined to form a relatively simple physical picture of the whole event.

scholarly journals Multiwavelength Observations of Fast Radio Bursts

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 76
Author(s):  
Luciano Nicastro ◽  
Cristiano Guidorzi ◽  
Eliana Palazzi ◽  
Luca Zampieri ◽  
Massimo Turatto ◽  
...  
Keyword(s):  
Radio Burst ◽  
High Energy ◽  
Medium Size ◽  
Radio Bursts ◽  
Starting Point ◽  
Key Points ◽  
Fast Radio Burst ◽  
Theoretical Results ◽  
Observational Strategy ◽  
Shed Light

The origin and phenomenology of the Fast Radio Burst (FRB) remains unknown despite more than a decade of efforts. Though several models have been proposed to explain the observed data, none is able to explain alone the variety of events so far recorded. The leading models consider magnetars as potential FRB sources. The recent detection of FRBs from the galactic magnetar SGR J1935+2154 seems to support them. Still, emission duration and energetic budget challenge all these models. Like for other classes of objects initially detected in a single band, it appeared clear that any solution to the FRB enigma could only come from a coordinated observational and theoretical effort in an as wide as possible energy band. In particular, the detection and localisation of optical/NIR or/and high-energy counterparts seemed an unavoidable starting point that could shed light on the FRB physics. Multiwavelength (MWL) search campaigns were conducted for several FRBs, in particular for repeaters. Here we summarize the observational and theoretical results and the perspectives in view of the several new sources accurately localised that will likely be identified by various radio facilities worldwide. We conclude that more dedicated MWL campaigns sensitive to the millisecond–minute timescale transients are needed to address the various aspects involved in the identification of FRB counterparts. Dedicated instrumentation could be one of the key points in this respect. In the optical/NIR band, fast photometry looks to be the only viable strategy. Additionally, small/medium size radiotelescopes co-pointing higher energies telescopes look a very interesting and cheap complementary observational strategy.

An Observational Revisit of Stationary Type IV Solar Radio Bursts

Solar Physics ◽  
2021 ◽  
Vol 296 (2) ◽  
Author(s):  
Maoshui Lv ◽  
Yao Chen ◽  
V. Vasanth ◽  
Mohd Shazwan Radzi ◽  
Zamri Zainal Abidin ◽  
...  
Keyword(s):  
Solar Radio ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
Type Iv ◽  
Stationary Type

scholarly journals No Evidence for Galactic Latitude Dependence of the Fast Radio Burst Sky Distribution

2021 ◽  
Vol 923 (1) ◽  
pp. 2 ◽  
Author(s):  
A. Josephy ◽  
P. Chawla ◽  
A. P. Curtin ◽  
V. M. Kaspi ◽  
M. Bhardwaj ◽  
...  
Keyword(s):  
Radio Burst ◽  
Sensitivity Threshold ◽  
Galactic Latitude ◽  
Radio Bursts ◽  
Intensity Mapping ◽  
Latitude Dependence ◽  
Kolmogorov Smirnov ◽  
Coin Flipping ◽  
Fast Radio Burst ◽  
Anderson Darling

Abstract We investigate whether the sky rate of fast radio bursts (FRBs) depends on Galactic latitude using the first catalog of FRBs detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project. We first select CHIME/FRB events above a specified sensitivity threshold in consideration of the radiometer equation, and then we compare these detections with the expected cumulative time-weighted exposure using Anderson–Darling and Kolmogorov–Smirnov tests. These tests are consistent with the null hypothesis that FRBs are distributed without Galactic latitude dependence (p-values distributed from 0.05 to 0.99, depending on completeness threshold). Additionally, we compare rates in intermediate latitudes (∣b∣ < 15°) with high latitudes using a Bayesian framework, treating the question as a biased coin-flipping experiment–again for a range of completeness thresholds. In these tests the isotropic model is significantly favored (Bayes factors ranging from 3.3 to 14.2). Our results are consistent with FRBs originating from an isotropic population of extragalactic sources.

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