Tracking of an electron beam through the solar corona with LOFAR

Mann, G.; Breitling, F.; Vocks, C.; Auraß, H.; Steinmetz, Matthias; Strassmeier, K. G.; Bisi, M. M.; Fallows, R. A.; Gallagher, Peter T.; Kerdraon, A.; MacKinnon, A. L.; Magdalenić, Jasmina; Rücker, H. O.; Anderson, J. M.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, Mark J.; Bernardi, G.; Best, P. N.; Bîrzan, L.; Bonafede, A.; Broderick, J. W.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Gasperin, F. de; Geus, E. de; Deller, Adam T.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fender, R. P.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.-M.; Gunst, A. W.; Haarlem, M. van; Hassall, T. E.; Heald, G.; Hessels, J. W. T.; Hoeft, M.; Hörandel, J. R.; Horneffer, A.; Juette, E.; Karastergiou, A.; Klijn, Wouter; Kondratiev, V. I.; Krämer, M.; Kuniyoshi, M.; Küper, G.; Maat, P.; Markoff, Sera; McFadden, R.; McKay-Bukowski, D.; McKean, J. P.; Mulcahy, D. D.; Munk, H.; Nelles, A.; Norden, M. J.; Orrù, E.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A. G.; Rafferty, D. A.; Reich, W.; Röttgering, H. J. A.; Scaife, A.; Schwarz, Dominik J.; Serylak, M.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Tagger, M.; Tang, Y.; Tasse, C.; Veen, S. ter; Thoudam, Satyendra; Toribio, M. C.; Vermeulen, R. C.; Weeren, R. J. van; Wise, Michael; Wucknitz, O.; Yatawatta, S.; Zarka, Philippe; Zensus, J. A.

doi:10.1051/0004-6361/201629017

Cited by 28 publications

(22 citation statements)

References 25 publications

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Section: Beam Velocity Evolutionmentioning

confidence: 60%

“…An increase in the inferred beam velocity from type III bursts has recently been reported by Mann et al (2018) using LOFAR imaging observations below 100 MHz. Mann et al (2018) derive velocities from the onset time of the type III burst at different frequencies and found huge increases in derived beam velocities around 30 MHz, with some bursts reported as superluminal. Whilst the effect we describe above can increase the derived beam velocity from radio bursts, and could play a role in the findings of Mann et al (2018), it is not likely to explain three-fold increases in velocities, nor provide superluminal velocities.…”

Section: Beam Velocity Evolutionmentioning

confidence: 60%

“…Mann et al (2018) derive velocities from the onset time of the type III burst at different frequencies and found huge increases in derived beam velocities around 30 MHz, with some bursts reported as superluminal. Whilst the effect we describe above can increase the derived beam velocity from radio bursts, and could play a role in the findings of Mann et al (2018), it is not likely to explain three-fold increases in velocities, nor provide superluminal velocities. Whilst refraction effects are considered, radio wave scattering at LOFAR frequencies has a more dominant effect (see Kontar et al 2017), is likely to increase the derived beam speeds and could explain the apparent beam acceleration.…”

Section: Beam Velocity Evolutionmentioning

confidence: 98%

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Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Reid

Kontar

2018

ApJ

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A component of space weather, electron beams are routinely accelerated in the solar atmosphere and propagate through interplanetary space. Electron beams interact with Langmuir waves resulting in type III radio bursts. Electron beams expand along the trajectory, and using kinetic simulations, we explore the expansion as the electrons propagate away from the Sun. Specifically, we investigate the front, peak and back of the electron beam in space from derived radio brightness temperatures of fundamental type III emission. The front of the electron beams travelled at speeds from 0.2c-0.7c, significantly faster than the back of the beam that travelled between 0.12c-0.35c. The difference in speed between the front and the back elongates the electron beams in time. The rate of beam elongation has a 0.98 correlation coefficient with the peak velocity; in-line with predictions from type III observations. The inferred speeds of electron beams initially increase close to the acceleration region and then decrease through the solar corona. Larger starting densities and harder initial spectral indices result in longer and faster type III sources. Faster electron beams have higher beam energy densities, produce type IIIs with higher peak brightness temperatures and shorter FWHM durations. Higher background plasma temperatures also increase speeds, particularly at the back of the beam. We show how our predictions of electron beam evolution influences type III bandwidth and drift-rates. Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.

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Section: Beam Velocity Evolutionmentioning

confidence: 60%

Section: Beam Velocity Evolutionmentioning

confidence: 60%

Section: Beam Velocity Evolutionmentioning

confidence: 98%

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Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Reid

Kontar

2018

ApJ

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“…Radio imaging of these bursts at a wide range of densely sampled frequencies with a sufficiently high temporal cadence can be used to map the detailed trajectory of a propagating electron beams in the corona, providing an excellent means of tracing these beams to their acceleration sites. Previous radio imaging of type III bursts (and their variants such as type J and U bursts) at one or several discrete frequencies, particularly from solar-dedicated Culgoora, Clark Lake, and Nançay radioheliographs, as well as general-purpose radio interferometers such as the Very Large Array, has yielded important results on the location and propagation of electron beams in the corona (e.g., Dulk & Suzuki 1980;Gopalswamy et al 1987;Aschwanden et al 1992;Paesold et al 2001;Klein et al 2008;Saint-Hilaire et al 2013;Carley et al 2016 (Morosan et al 2014;Kontar et al 2017;Reid & Kontar 2017;McCauley et al 2017;Mann et al 2018;Cairns et al 2018). However, in order to trace the electron beams to the immediate vicinity of the primary magnetic energy release and electron acceleration site, presumably located in the low corona where the plasma is denser (typically at the order of 10 10 cm −3 ; Aschwanden 2002; Krucker et al 2008), spectral imaging of type III bursts at shorter, decimetric wavelengths ("dm-λ" hereafter) is preferred because ν pe , which increases monotonically with n e , falls into this wavelength range.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Reconnection Null Points as the Origin of Semirelativistic Electron Beams in a Solar Jet

Bin

Battaglia

et al. 2018

ApJ

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Magnetic reconnection, the central engine that powers explosive phenomena throughout the Universe, is also perceived as one of the principal mechanisms for accelerating particles to high energies. Although various signatures of magnetic reconnection have been frequently reported, observational evidence that links particle acceleration directly to the reconnection site has been rare, especially for space plasma environments currently inaccessible to in situ measurements. Here we utilize broadband radio dynamic imaging spectroscopy available from the Karl G. Jansky Very Large Array to observe decimetric type III radio bursts in a solar jet with high angular (∼20 ), spectral (∼1%), and temporal resolution (50 milliseconds). These observations allow us to derive detailed trajectories of semi-relativistic (tens of keV) electron beams in the low solar corona with unprecedentedly high angular precision (< 0 .65). We found that each group of electron beams, which corresponds to a cluster of type III bursts with 1-2-second duration, diverges from an extremely compact region (∼600 km 2 ) in the low solar corona. The beam-diverging sites are located behind the erupting jet spire and above the closed arcades, coinciding with the presumed location of magnetic reconnection in the jet eruption picture supported by extreme ultraviolet/X-ray data and magnetic modeling. We interpret each beam-diverging site as a reconnection null point where multitudes of magnetic flux tubes join and reconnect. Our data suggest that the null points likely consist of a high level of density inhomogeneities possibly down to 10-km scales. These results, at least in the present case, strongly favor a reconnection-driven electron acceleration scenario.

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“…The trapped radio waves only leave the flux tube at the apparent source position when the wave frequency inside the tube is greater than the plasma frequency outside. Such displacements of the apparent radio source have also been seen in radio images from the LOw Frequency ARray (LOFAR; Kontar et al 2017;Mann et al 2018) at metric wavelengths. Based on a study of fine structures of Type III radio bursts using LOFAR observations, Kontar et al (2017) suggested that the apparent source locations of fundamental and harmonic emission result from the scattering of radio waves by coronal density inhomogeneities.…”

Section: Introductionmentioning

confidence: 73%

Decimetric Emission 500″ Away from a Flaring Site: Possible Scenarios from GMRT Solar Radio Observations

Sawant

Janardhan

Yan³

et al. 2018

ApJ

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We present a study of decimetric radio activity using the first high time cadence (0.5 s) images from the Giant Meterwave Radio Telescope (GMRT) at 610 MHz associated with GOES C1.4-and M1.0-class solar flares and a coronal mass ejection (CME) onset that occurred on 2015 June 20. The high spatial resolution images from GMRT show a strong radio source during the C1.4 flare located ∼500″ away from the flaring site with no corresponding bright footpoints or coronal features nearby. In contrast, however, strong radio sources are found near the flaring site during the M1.0 flare and around the CME onset time. Weak radio sources located near the flaring site are also found during the maximum of the C1.4 flare activity that show a temporal association with metric Type III bursts identified by the Solar Broadband Radio Spectrometer at Yunnan Astronomical Observatory. Based on a multiwavelength analysis and magnetic potential field source surface extrapolations, we suggest that the source electrons of GMRT radio sources and metric Type III bursts originated from a common electron acceleration site. We also show that the strong GMRT radio source is generated by a coherent emission process, and its apparent location far from the flaring site is possibly due to the wave-ducting effect.

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Tracking of an electron beam through the solar corona with LOFAR

Cited by 28 publications

References 25 publications

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona

Magnetic Reconnection Null Points as the Origin of Semirelativistic Electron Beams in a Solar Jet

Decimetric Emission 500″ Away from a Flaring Site: Possible Scenarios from GMRT Solar Radio Observations

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