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Unexpected spatial intensity distributions and onset timing of solar electron events observed by closely spaced STEREO spacecraft  

Andreas Klassen   Submitted: 2016-06-20 06:53

We present multi-spacecraft observations of four solar electron events using measurements from the Solar Electron Proton Telescope (SEPT) and the Electron Proton Helium INstrument (EPHIN) on board the STEREO and SOHO spacecraft, respectively, occurring between 11 October 2013 and 1 August 2014, during the approaching superior conjunction period of the two STEREO spacecraft. At this time the longitudinal separation angle between STEREO-A (STA) and STEREO-B (STB) was less than 72 ◦ . The parent particle sources (flares) of the four investigated events were situated close to, in between, or to the west of the STEREO's magnetic footpoints. The STEREO measurements revealed a strong difference in electron peak intensities (factor ≤12) showing unexpected intensity distributions at 1 AU, although the two spacecraft had nominally nearly the same angular magnetic footpoint separation from the flaring active region (AR) or their magnetic footpoints were both situated eastwards from the parent particle source. Furthermore, the events detected by the two STEREO imply a strongly unexpected onset timing with respect to each other: the spacecraft magnetically best connected to the flare detected a later arrival of electrons than the other one. This leads us to suggest the concept of a rippled peak intensity distribution at 1 AU formed by narrow peaks (fingers) superposed on a quasi-uniform Gaussian distribution. Additionally, two of the four investigated solar energetic particle (SEP) events show a so-called circumsolar distribution and their characteristics make it plausible to suggest a two-component particle injection scenario forming an unusual, non-uniform intensity distribution at 1 AU.

Authors: A. Klassen, N. Dresing, R. Gómez-Herrero, B. Heber, R. Müller-Mellin
Projects: STEREO

Publication Status: A&A accepted
Last Modified: 2016-06-22 09:12
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First simultaneous observations of a near-relativistic electron spike event by both STEREO spacecraft  

Andreas Klassen   Submitted: 2015-06-29 01:52

Solar electron spike events are a special subclass of near-relativistic electron events characterized by their short duration, symmetric time profile, and their strong anisotropic pitch angle distribution. All previous studied events were only observed by a single spacecraft. For the first time, we present measurements of this kind of an electron spike event that was observed simultaneously by both close- spaced STEREO spacecraft on 2 May 2014. The longitudinal separation angle between STEREO-A (STA) and STEREO-B (STB) was 38◦ . The spikes at STA and STB are characterized by very short durations of ≤ 12 minutes at full-width at half maximum (FWHM) and almost identical and symmetric time profiles. They exhibit similar properties in durations, pitch angle distributions (PADs), energy spectra, and peak intensities. The spike parent source was situated close to the STA nominal magnetic footpoint and was separated by 48 ◦ from STB?s footpoint. The intensity distribution and the relative onset timing behaved opposite to what is expected: STB measured a higher intensity and an earlier onset than the nominally better connected STA. We suggest that the spike electrons undergo a substantial nonradial injection into interplanetary (IP) space from the parent source, a flaring active region (AR), and propagate in a strong nonradial diverging magnetic field. In addition we show that because of the spike properties it is evident that, irrespective of how the electrons were injected into the IP medium, the en route particle scattering conditions along the paths to STA and STB were very similar. Evidently both s/c detected different parts of the same beam whose angular extension was at least 38◦ at 1 AU, comparable to the longitudinal separation between STA and STB.

Authors: A. Klassen, N. Dresing, R. Gómez-Herrero, B. Heber
Projects: STEREO

Publication Status: A&A, accepted
Last Modified: 2015-06-29 11:55
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Solar origin of in-situ near-relativistic electron spikes observed with SEPT/STEREO  

Andreas Klassen   Submitted: 2012-04-19 04:07

During 2010 - 2011 the Solar Electron Proton Telescope (SEPT) onboard the twin STEREO spacecraft detected a number of typical impulsive electron events showing a prompt intensity onset followed by a long decay, as well as several near-relativistic so-called electron spike events. These spikes are characterized by a very short duration of below 10 - 20 min at FWHM, almost symmetric time profiles, velocity dispersion and strong anisotropy, revealing a very weak scattering during particle propagation from the Sun to STEREO. Spikes are detected at energies below 300 keV and appear simulateneously with type III radio bursts detected by SWAVES/STEREO and narrow EUV jets in active regions. Using particle, EUV and radio imaging observations we found that nearrelativistic electrons were accelerated simultaneously and at the same location as the electrons emitting the accompanying type III radio bursts and together with coronal EUV jets. Furthermore, the sources of type III radio bursts match very well the locations and the trajectories of the associated EUV jet. Applying a particle propagation model we demonstrate that the spike characteristics reflect both, properties of the accelerator and effects of interplanetary propagation.

Authors: A. Klassen, R. Gómez-Herrero, B. Heber, Y. Kartavykh, W. Dr?ge, K.-L. Klein
Projects: STEREO

Publication Status: Astronomy & Astrophysics, accepted
Last Modified: 2012-04-19 09:37
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The almost monoenergetic ion event on 19 October 2009: SEPT/STEREO observations  

Andreas Klassen   Submitted: 2011-03-04 02:00

The Solar Electron and Proton Telescope (SEPT) on board the twin spacecraft STEREO A and B measures electrons and ions in the energy range from 60 to above 400 keV with an energy resolution of 10%. On 19 October 2009, when STEREO-B was already 1.03 AU away from the Earth, a strong and prolonged almost monoenergetic ion event has been observed with the SEPT instrument. The event lasted 27 minutes and its energy spectrum contained a strong narrow peak at 235 keV with a relative full width at half maximum of 0.35. The event occurred during a period of slow solar wind in front of a weak ion increase associated with a distant corotating interaction region (CIR). Previously similar events containing spectral peaks were detected in the vicinity of the Earth's magnetosphere using observations on Interball-1 and on both STEREO A & B spacecraft. We present evidence that the narrow spectral peak is caused by a quasi-monoenergetic ion beam and suggest that the particles were accelerated at a distant CIR or CIR shock. We discuss the possible mechanisms that could be responsible for accelerating these ions: the shock drift acceleration, the surfatron mechanism and the acceleration in a large-scale electrostatic field.

Authors: A. Klassen, R. Gómez-Herrero, R. Müller-Mellin, B. Heber, R. F. Wimmer-Schweingruber, A. Opitz, and J.-A. Sauvaud
Projects: STEREO

Publication Status: Accepted for publication in A&A
Last Modified: 2011-03-04 06:36
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Electron spikes, type III radio bursts and EUV jets on 22 February 2010  

Andreas Klassen   Submitted: 2011-03-04 01:50

The Solar Electron Proton Telescope on board the twin STEREOspacecraft measures electrons and ions in the energy range from 30 toabove 400 keV with an energy resolution better than 10%. On 22February 2010 during a short interval of 100 minutes, a sequence ofimpulsive energetic electron events in the range below 120 keV wasobserved with the STEREO-A/SEPT instrument. Each of the four eventswas associated with a type III radio burst and a narrow EUV jet. Allthe events show nearly symmetric ''spike''-like time profiles withvery short durations ≈5 min. The estimated electron injectiontime for each individual event shows a small time delay between theelectron spike and the corresponding type III radio emission and aclose coincidence with an EUV jet. These observations reveal theexistence of spike-like electron events showing nearly''scatter-free'' propagation from the Sun to STEREO-A. From the timecoincidence we infer that the mildly relativistic electrons areaccelerated at the same time and at the same location as theaccompanying type III emitting electrons and coronal EUV jets. Thecharacteristics of the spikes reflect the injection and accelerationprofiles in the corona rather than the interplanetary propagationeffects.

Authors: A. Klassen, R. Gómez-Herrero, B. Heber
Projects: STEREO

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2011-03-04 06:36
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Type II radio precursor and X-ray flare emission  

Andreas Klassen   Submitted: 2003-09-11 02:17

The formation of a radio emitting shock wave and its precursor above a flaring active region is investigated during the flare on 12 April 2001. Using combined spectral and imaging observations of radio bursts with Yohkoh soft and hard X-ray imaging observations, we confirm earlier findings that the type II bursts are generated in association with and above expanding soft X-ray loops. The type II precursor is identified as a signature of the reconnection process above the expanding soft X-ray loops which later generate the type II burst. The precursor emission consists of fast reverse drift bursts that reveal electron beams propagating towards the expanding loops and the hard X-ray sources. There is some degree of similarity between the radio bursts and the rising hard X-ray time profile. This suggests a close relation between the precursor and the soft and hard X-ray sources, i.e. signatures of the primary energy release during the flare. We found that the speeds of the expanding loops <=700 km s-1, of the precursor =~950 km s-1, and of the type II exciter =~900-1400 km s-1 are comparable. But the expanding loops have the lowest speed.

Authors: Klassen, A., Pohjolainen, S., and Klein, K.-L.
Projects: Yohkoh-HXT,Yohkoh-SXT

Publication Status: Solar Physics (accepted)
Last Modified: 2003-09-11 02:17
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Superluminal apparent velocities of relativistic electron beams in the solar corona  

Andreas Klassen   Submitted: 2003-08-11 04:15

We present spectral and imaging observations of high frequency type III bursts appearing in pairs: a primary fast drifting component and a secondary ''normal'' drifting component. The primary bursts have generally higher frequency drift and start at higher frequencies. They show superluminal velocities up to 2.5 c (c, speed of light), while the secondary component shows the usual < 0.5 c velocity expected for type III burst exciters. These superluminal velocities are explained as apparent velocities of relativistic electron beams propagating nearly along the line of sight towards the observer with velocities close to the speed of light. A model of type III burst pairs consisting of subsequent fast drifting and ''normal'' drifting components is presented.

Authors: A. Klassen, M. Karlický, and G. Mann
Projects: None

Publication Status: A&A (accepted)
Last Modified: 2003-08-11 04:15
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Abstracts by Author
Unexpected spatial intensity distributions and onset timing of solar electron events observed by closely spaced STEREO spacecraft
First simultaneous observations of a near-relativistic electron spike event by both STEREO spacecraft
Solar origin of in-situ near-relativistic electron spikes observed with SEPT/STEREO
The almost monoenergetic ion event on 19 October 2009: SEPT/STEREO observations
Electron spikes, type III radio bursts and EUV jets on 22 February 2010
Type II radio precursor and X-ray flare emission
Superluminal apparent velocities of relativistic electron beams in the solar corona

Related Pages
MSU Solar Physics.
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Max Millennium Flare Catalog

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