I am pleased to invite you to the defense of my PhD thesis. It will be held on Thursday, December 4, 2025, at 2:00 PM, at the Meudon Observatory (Building 18, Evry Schatzman Amphitheatre). The event will also be streamed live via the LIRA YouTube channel.
Jury composition:
- Christophe LEPONCIN-LAFITTE Président du jury, LTE, Observatoire de Paris
- Astrid VERONIG Rapporteur, Institute of Physics, University of Graz
- Jasmina MAGDALENIC Rapporteur, Plasma-Astrophysics, KU Leuven
- Alexander WARMUTH Examinateur, AIP, Leibniz Institute for Astrophysics Postdam
- Hamish REID Examinateur, MSSL, University College London
- Sophie MASSON Examinateur, LPP, Observatoire de Paris
- Nicole VILMER Directeur de thèse, LIRA, Observatoire de Paris
- Milan MAKSIMOVIC Co-directeur de thèse, LIRA, Observatoire de Paris
Title:
« Energetic Particles in Solar Flares: Diagnostics with X-ray and Radio Observations from Solar Orbiter »
Abstract:
The Sun is a powerful particle accelerator. During solar flares a large amount of energy stored in the sun’s magnetic fields is released. An important fraction of this energy goes into accelerated particles, which can reach relativistic velocities. The electrons that propagate sunward produce Hard X-ray (HXR) bremsstrahlung emission. Electrons that propagate outwards though open field lines produce type III radio bursts into the Corona and interplanetary (IP) space. Despite the sometimes close relation observed between the two emissions suggest a common accelerator for associated events, the relationship between HXR flares and IP type III bursts is not well established. The two statistical studies presented in this PhD work use the STIX (HXR) and RPW (radio) instruments on Solar Orbiter to investigate this link.
In the first study, we analyzed the first available period of simultaneous HXR and radio observation. The analysis of 15 IP type III bursts with temporally associated HXR flares revealed that the onset of radio bursts, which is often not associated with the main HXR during the flare, is consistently preceded by a reconfiguration of the HXR source morphology. This suggests complex scenarios for reconnection where the evolution of the magnetic morphology of the flare lead to late episodes of reconnection with open field lines enabling electron escape. The second study describes a more quantitative relation of these emissions where 38 HXR/radio events were analyzed. Type III bursts with higher peak flux or that show higher exciter velocities are to higher non-thermal electron power and harder electron spectra (lower spectral index) derived from HXR spectroscopy. These results support a common accelerator and show that the peak flux and the velocity derived from type III emission reflect the energy content of the radio-emitting electrons, as predicted by numerical simulations.
(Transmis par David Paipa)