Radio Submillimeter and γ-Ray Observations of the 2003 October 28 Solar Flare

• Published in: The Astrophysical journal 2008-05, Vol.678 (1), p.509-514
• Main Authors: Trottet, G, Krucker, Säm, Lüthi, T, Magun, A
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Sciences of the Universe
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/528787

Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA (BEMRAK) are combined with hard X-ray and γ-ray observations from the SONG instrument on board CORONA-F and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to investigate high-energy particle acceleration during the energetic solar flare of 2003 October 28. Two distinct components at submillimeter wavelengths are found. The first is a gradual, long-lasting (>30 minutes) component with large apparent source sizes (~60''). Its spectrum below ~200 GHz is consistent with synchrotron emission from flare-accelerated electrons producing hard X-ray and γ-ray bremsstrahlung assuming a magnetic field strength of >=200 G in the radio source and a confinement time of the radio-emitting electrons in the source of less than 30 s. The other component is impulsive and starts simultaneously with high-energy (>200 MeV nucleon-1) proton acceleration and the production of pions. The derived radio source size is compact (30 MeV protons as seen in γ-ray imaging. The close correlation in time and space of radio emission with the production of pions suggests that synchrotron emission of positrons produced in charged-pion decay might be responsible for the observed compact radio source. However, order-of-magnitude approximations rather suggest that the derived numbers of positrons from charged-pion decay are probably too small to account for the observed radio emission. Synchrotron emission from energetic electrons therefore appears as the most likely emission mechanism for the compact radio source seen in the impulsive phase, although it does not account for its close correlation, in time and space, with pion production.