An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles

Abstract

The famous extreme solar and particle event of 20 January 2005 is analyzed from two perspectives. Firstly, using multi-spectral data, we study temporal, spectral, and spatial features of the main phase of the flare, when the strongest emissions from microwaves up to 200 MeV gamma-rays were observed. Secondly, we relate our results to a long-standing controversy on the origin of solar energetic particles (SEP) arriving at Earth, i.e., acceleration in flares, or shocks ahead of coronal mass ejections (CMEs). Our analysis shows that all electromagnetic emissions from microwaves up to 2.22 MeV line gamma-rays during the main flare phase originated within a compact structure located just above sunspot umbrae. In particular, a huge (≈ 10 5 sfu) radio burst with a high frequency maximum at 30 GHz was observed, indicating the presence of a large number of energetic electrons in very strong magnetic fields. Thus, protons and electrons responsible for various flare emissions during its main phase were accelerated within the magnetic field of the active region. The leading, impulsive parts of the ground-level enhancement (GLE), and highest-energy gamma-rays identified with π 0 -decay emission, are similar and closely correspond in time. The origin of the π 0 -decay gamma-rays is argued to be the same as that of lower-energy emissions, although this is not proven. On the other hand, we estimate the sky-plane speed of the CME S.N. Kuznetsov deceased 17 May 2007. 150 V.V. Grechnev et al.to be 2 000 -2 600 km s −1 , i.e., high, but of the same order as preceding non-GLE-related CMEs from the same active region. Hence, the flare itself rather than the CME appears to determine the extreme nature of this event. We therefore conclude that the acceleration, at least, to sub-relativistic energies, of electrons and protons, responsible for both the major flare emissions and the leading spike of SEP/GLE by 07 UT, are likely to have occurred nearly simultaneously within the flare region. However, our analysis does not rule out a probable contribution from particles accelerated in the CME-driven shock for the leading GLE spike, which seemed to dominate at later stages of the SEP event.

The relativistic solar particle event of 2005 January 20: origin of delayed particle acceleration

“…The energy release starting 06:54 UT thus involved part of the structures that brightened in the impulsive phase (kernels 1, 2) and newly brightening kernels of pairs (5, 6) et (7,8) that probably relate to more extended coronal magnetic structures than the previous episodes, because the kernels are further apart than previously. The first post flare loops became visible between the flare ribbons in TRACE UV images at about 7:04 UT, well after the brightening of these flare kernels, and persisted throughout the day (Grechnev et al 2008). The kernels (5, 6) and (7, 8) thus signal a distinct early energy release process during Episode 5, but the subsequent appearance of post flare loops suggests that energy release continued at increasing coronal height.…”

“…3.2. The 2005 Jan. 20 event was clearly eruptive, with a fast CME (Grechnev et al 2008) and an EUV wave (Miteva et al 2014). These phenomena were very likely accompanied by shock waves and therefore Type II radio bursts.…”

“…It displayed a well-defined, rapidly rising time profile at the beginning and a distinct second peak a few minutes later. Evidence that the first release was related to particle acceleration in the flaring active region in the low corona was brought by different publications (e.g., Simnett 2006Simnett , 2007Kuznetsov et al 2008;Grechnev et al 2008;McCracken et al 2008;Masson et al 2009). In the present paper we complete the investigation of Masson et al (2009, hereafter Paper I) through a detailed comparison between the second peak of the relativistic proton time profile derived from neutron monitor measurements with high-quality radio and UV observations.…”

What Are Special About Ground-Level Events?

“…Another view, however, is that some GLEs come directly from solar flares, which may also accelerate particles to high energies in magnetic reconnection, primarily because their temporal variations mimic those of impulsive flares (Grechnev et al 2008;McCracken et al 2008). Aschwanden (2012) also argued that, in five of the 13 GLEs he studied, the particles are released during the impulsive phase of the associated flare.…”

The Origin of Superflares on G-Type Dwarf Stars of Various Ages

“…The idea by Livshits and Belov (2004) about efficient particle acceleration above spots was reliably confirmed by Grechnev et al (2008) by an analysis of the whole set of observational data for the flare on Before the discussion of a model of superflares, let us summarize briefly the knowledge on the appearance of the flare optical continuum. Short brightness enhancement was registered quite rarely in small regions of about a few arcsec.…”