Modeling solar near-relativistic electron events

Abstract

Context. Solar near-relativistic electrons (>30 keV) are observed as discrete events in the inner heliosphere following different types of solar transient activity. Several mechanisms have been proposed for the production of these electrons. One candidate is related to solar flare activity. Other candidates include shocks driven by fast coronal mass ejections (CMEs) or processes of magnetic reconnection in the aftermath of CMEs. Aims. We study eleven near-relativistic (NR) electron events observed by the Advanced Composition Explorer (ACE) between 1998 and 2005 with the aim of estimating the roles played by solar flares, CME-driven shocks, and processes of magnetic restructuring in the aftermath of the CMEs in the injection of NR electrons. The main goal is to infer the underlying injection profile from particle observations at 1 AU, as well as the interplanetary transport conditions. Methods. We used Monte Carlo simulations to model the transport of particles along the interplanetary magnetic field. By taking the angular response of the LEFS60 telescope of the EPAM instrument onboard ACE into account, we were able to deconvolve the transport effects from the observed intensities, and thus infer the solar injection profile. Results. In this set of events, we have identified two types of injection episodes: short (<15 min) and time-extended (>1 h). Short injection episodes seem to be associated with the flare processes and/or the reconnection phenomena in the aftermath of the CME, while time-extended episodes seem to be consistent with injection from CME-driven shocks. Conclusions. We find that there is no single scenario that operates in all the events. The interplanetary propagation of NR electrons can occur both under strong scattering and under almost scatter-free propagation conditions and several injection phases (related to flares and/or CMEs) are possible.

A diffusive description of the focused transport of solar energetic particles

“…Bieber et al (2004) conclude that the onset of particle injection onto the Sun-Earth field line was at 13:42 UT ± 1 min, and Agueda et al (2009) conclude that the electron injection started at 13:48 UT at 80 keV. These two previous results are in accordance with our injection time at 13:45 UT.…”

“…Dröge (2005) modeled the event by assuming a spatially constant radial mean free path for 511 keV electrons and concludes that λ r = 0.14 AU (λ = 0.24 AU at Earth). Similarly, Agueda et al (2009) estimate the radial mean free path of the 62−312 keV electrons is 0.08 AU (λ = 0.17 AU at Earth). At the distance of the Earth these agree with our result:…”

Solar near-relativistic electron observations as a proof of a back-scatter region beyond 1 AU during the 2000 February 18 event

“…We infer the interplanetary transport conditions and the injection time profile at the Sun from a set of in-situ measured sectored intensities by using the inversion technique presented in Agueda et al (2008) and Agueda et al (2009b). By taking the angular response of the sectors scanned by the LEFS60 telescope into account, it is possible to transform the simulated PADs into sectored intensities measured by the telescope (Agueda et al 2008).…”

“…This ensures that the directional information contained in the data is used in full to explain the event. Agueda et al (2010) concluded that the electron directional intensities observed on 2000 February 18 could not be explained without the assumption of a back-scatter region beyond 1 AU. But scatter-free propagation inside 1 AU predicted PADs more collimated than the observed ones.…”

“…with increasing heliocentric radial distance. Agueda et al (2010) explored the first approach by using Monte Carlo simulations of the particle transport along an Archimedean interplanetary magnetic field. Their goal was to fit the 2000 February 18 electron event observed by the LEFS60 telescope of the EPAM experiment on board ACE (Gold et al 1998) making use of observational sectored intensities.…”