Solar source of energetic particles in interplanetary space during the 2006 December 13 event

¹ Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK e-mail: cl2@mssl.ucl.ac.uk
² Institut d'Astrophysique Spatiale, Universit Paris-sud 11 and CNRS, 91405 Orsay, France
³ Department of Astronomy, Nanjing University, Nanjing 210093, PR China

Received: 4 March 2009
Accepted: 12 June 2009

Abstract

An X3.4 solar flare and a fast halo coronal mass ejection (CME) occurred on 2006 December 13, accompanied by a high flux of energetic particles recorded both in near-Earth space and at ground level. Our purpose is to provide evidence of flare acceleration in a major solar energetic particle (SEP) event. We first present observations from ACE/EPAM, GOES, and the Apatity neutron monitor. It is found that the initial particle release time coincides with the flare emission and that the spectrum becomes softer and the anisotropy becomes weaker during particle injection, indicating that the acceleration source changes from a confined coronal site to a widespread interplanetary CME-driven shock. We then describe a comprehensive study of the associated flare active region. By use of imaging data from HINODE/SOT and SOHO/MDI magnetogram, we infer the flare magnetic reconnection rate in the form of the magnetic flux change rate. This correlates in time with the microwave emission, indicating a physical link between the flare magnetic reconnection and the acceleration of nonthermal particles. Combining radio spectrograph data from Huairou/NOAC, Culgoora/IPS, Learmonth/RSTN, and WAVES/WIND leads to a continuous and longlasting radio burst extending from a few GHz down to several kHz. Based on the photospheric vector magnetogram from Huairou/NOAC and the nonlinear force free field (NFFF) reconstruction method, we derive the 3D magnetic field configuration shortly after the eruption. Furthermore, we also compute coronal field lines extending to a few solar radii using a potential-field source-surface (PFSS) model. Both the so-called type III-l burst and the magnetic field configuration suggest that open-field lines extend from the flare active region into interplanetary space, allowing the accelerated and charged particles escape.