Conveners
Working Group 2: Particle acceleration
- Diana E. Morosan (Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland.)
- Silvina Guidoni (American University)
Description
X-ray and radio imaging and spectroscopy observations yield essential information for the understanding of plasma heating and the acceleration and transport of high-energy particles in solar eruptive events. Radio data provides plasma, magnetic field, and particle diagnostics in the corona and complements hard X-ray diagnostics in the chromosphere and dense coronal structures. The next generation of missions (e.g., Solar Orbiter/STIX) and advanced radio telescopes will bring light to currently unanswered questions, but also introduce new challenges and questions. It is likely that substantial progress in the field can only be achieved by collaborative work among observers and modelers. Therefore, this working group welcomes contributions on recent results in X-ray and radio observations, especially those addressing the complementary nature of radio and X-ray observations, as well as advances in associated particle acceleration models. We are also interested in studies that explore the limitations of high-energy observations and models, provide diagnostic tools or describe needed observations to constrain theories, and aim to develop a common language for scientists working in these areas or research.ย
NOTE: The times and duration of each talk are the true times and duration of the talks for this session.
Radio and hard X-ray diagnostics provide very strong complementary tools to probe electron acceleration in solar flares. With the Expanded Owens Valley Solar Array (EOVSA) and the Spectrometer/Telescope for Imaging X-rays (STIX) we have currently two solar dedicated observatories jointly observing on a daily basis. To date, we already have more than 10 jointly observed flares ranging from...
The Spectrometer/Telescope for Imaging X-rays (STIX) is the remote sensing instrument onboard Solar Orbiter dedicated to the observation of the X-ray emission during solar flares. The goal of the instrument is to provide information about the electron acceleration at the Sun through the measurement of the photons emitted by bremsstrahlung or by thermal mechanisms. The telescope consists of 30...
Like their larger counterparts, solar microflares release magnetic energy and accelerate particles to relativistic speeds. Even though they are generally shorter and often more compact than larger flares, they can display a surprising complexity and provide new insights into where and when particles are accelerated.
We present observations of multiple electron acceleration sites and times...
Solar flares release enormous magnetic energy into the corona, producing the heating of ambient plasma and the acceleration of particles. The flaring process is complex and often shows multiple spatially separated temporal individual episodes of energy releases, which can be hard to resolve based on the instrument capability. We analysed the multi-wavelength imaging and spectroscopy...
Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare occurred on 2017 September 6, using data obtained by the Expanded Owens Valley...
We investigate 16 solar energetic electron (SEE) events measured by WIND/3DP with a double-power-law spectrum and the associated western hard X-ray (HXR) flares measured by RHESSI with good count statistics, from 2002 February to 2016 December. In all the 16 cases, the presence of an SEE power-law spectrum extending down to ~5 keV at 1 au implies that the SEE source would be high in the...
Extensive observations have discovered that a huge number of energetic electrons with energy up to MeV (~0.9c and Lorentz factor ~2) are produced during solar flares. These very mild relativistic energetic electrons demonstrate two-stage power-law spectral evolutions. What mechanism efficiently accelerates non-relativistic particles to a power-law has been a long-standing โ injection problemโ...
Flares are violent explosions and natural particle accelerators in solar atmosphere. The accelerated particles play an essential role in flare energy release and distribution. High and low energy cutoffs define the upper and lower limits of accelerated electrons. They are important parameters in understanding particle acceleration and energy distribution. However, the existence of...
The origin of hard X-rays and ฮณ-rays emitted from the solar atmosphere during occulted solar flares is still debated. The hard X-ray emissions could come from flaring loop tops rising above the limb or coronal mass ejection shock waves, two by-products of energetic solar storms. For the shock scenario to work, accelerated particles must be released on magnetic field lines rooted on the visible...
Extreme-ultraviolet late phase (ELP) refers to the second extreme-ultraviolet (EUV) radiation enhancement in some solar flares, minutes or hours after the X-ray emission peak at the flare impulsive phase. ELP loops often have distinct configurations from the main flaring loops and the enhanced EUV emission may imply an additional heating process. Here we analyzed a C1.4 flare which has a...
We conduct the wide-band X-ray spectral analysis in the energy range of 1.5 keV-100 keV and study the time evolution of the thermal and non-thermal emission in the July 23, 2016 M7.6 Class solar flare observed with the Miniature X-ray Solar Spectrometer (MinXSS) CubeSat and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). As a result, the time evolution of multi-thermal and...
Solar flares are very efficient particle accelerators on a short timescale. The X-ray and type III radio emission emitted during a flare are direct signatures of the accelerated electrons. Hard X-rays are emitted from the accelerated electrons through bremsstrahlung radiation primarily in the dense atmosphere, while type III emissions are caused by the accelerated electrons propagating through...
During the gradual phase of flare SOL2017-09-09T10:50, a faint increase of non-thermal X-ray emission has been detected by Fermi/GBM, and is associated with radio decimetric spikes and type III radio bursts detected by the ORFEES radio-spectrograph, the LOFAR radio-telescope, and the Wind/WAVE instrument. These signatures indicate that a faint acceleration event was the source of electron...
We present observations of an M class flare with the LOw Frequency ARray (LOFAR) in the morning hours of 7 September 2017. The flare was accompanied by strong type III radio bursts. LOFAR interferometric images in the low band frequency range of 20 - 80 MHz show distinct sources that show variations in their positions, and intermittent dual source structures. We identify these as fundamental...
We present the preliminary results of the SOL 29-05-2020T07:20 flare study based on observations within the 4-8 GHz range by Siberian Radioheliograph 48, spectropolarimeter 4-8 GHz and the other available microwave (MW) data. The MW time profiles of the flare demonstrated at least three quasi-periodic bursts. The current study aims to find mechanisms generating the emission of the different...
In this contribution we present a study of 2 flare events (of M and C class) which were associated with Slowly Positively Drifting Burst (SPDBs) observed at radio frequencies in the range of 800-2000 MHz. These burst are similar to reverse type III burst but their drift is much less than < 1GHz/s and they are rarely observed. Both flare events started within an active region but later involved...
Flare Ribbon Signatures of Plasmoids
J. T. Dahlin
Solar flares are explosive space weather events that rapidly convert stored magnetic energy into bulk motion, plasma heating, and particle acceleration. Understanding the structure and dynamics of the magnetic reconnection that powers flares is critical for predicting the energy release. In particular, the amount of energy transferred to...
In this work, we seek to understand the relationships among magnetic reconnection, flare energy release and initiation/acceleration of coronal mass ejections (CMEs) for solar eruptive events. RHESSI, STEREO, and SDO data are utilized to study the relative timing between the HXR, CME acceleration, and reconnection rate profiles for 12 CME-flares. This analysis expands upon previous CME-flare...
The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite the large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well observed solar eruptive event that...
The Sun produces highly dynamic and eruptive events that can drive shocks through the corona.
These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio
burst. Despite a large number of type II radio bursts observations, the precise origin of coronal
shocks is still subject to investigation. Here we present a well-observed solar eruptive event...
The Sun frequently accelerates near-relativistic electron beams that travel out through the solar corona and interplanetary space. Undergoing wave-particle interactions with Langmuir waves, these beams are the driver for type III radio bursts, the brightest radio bursts produced by the Sun. The formation and motion of type III fine frequency structures is a puzzle but is commonly believed to...
Low frequency radio wave scattering and refraction can have a dramatic effect on the observed size and position of radio sources in the solar corona.
The scattering and refraction is thought to be due to fluctuations of electron density caused by turbulence. Hence, determining the true radio source size can provide information on the turbulence in coronal plasma.
However, the lack of high...
The solar corona is a highly-structured plasma which can reach temperatures of more than ?~2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to...
In solar and helio-physics, the coronal heating problem relates to the question of identifying and explaining the mechanism(s) causing the corona's temperatures to be a few hundred times hotter than the solar surface. Among the various plausible hypotheses proposed to explain this problem, one of the strongest candidates relates to copious low energy magnetic reconnections (nanoflares)...
