14-17 mai 2019


Particle acceleration in astrophysical and space plasmas


Alexis Rouillard (IRAP), Alexandre Marcowith, Illya Plotnikov, Sophie Masson


Plasmas encountered in astrophysics and heliophysics host explosive events that can accelerate particles to high energies including the most energetic particles in the universe. Known acceleration sites include the boundary of planetary magnetospheres, solar coronal mass ejections, solar flares, planetary magnetospheres, interacting massive star winds, pulsar magnetospheres, supernovae, supernova remnants, active galactic nuclei, gamma-ray bursters. These environments typically host strong interactions between different populations of turbulent magnetised plasmas. Physical processes encountered both in astrophysics and heliophysics include magnetic reconnection, rotating magnetic fields, stochastic acceleration and shock-associated particle acceleration (diffusive, drift,...), shear acceleration. In heliophysics the emergence of a coronal mass ejection and its intimate relationship with a flare is likely to involve several acceleration mechanisms acting simultaneously at different locations in space; this includes magnetic reconnection and stochastic particle acceleration in the wake of the mass ejection and fast shock waves in front of the ejection. Disentangling the relative contribution of each mechanism becomes then a challenge. Recent space missions such as the Magnetospheric Multiscale Mission (MMS) have measured in situ the physical processes involved in magnetic reconnection down to electron scales. New missions such as the Parker Solar Probe and the Solar Orbiter will over the next few years get closer to the Sun and visit other accelerators such as coronal shock waves. Parker Solar Probe in particular will plunge in the solar atmosphere and intersect shock waves where they are likely to be more efficient particle accelerators than near 1 AU. Unprecedented in-situ measurements of particles and fields near the shock should help us test the theory of diffusive-shock acceleration to the MeV - GeV range. In astrophysics the development of numerical resources have produced impressive simulations investigating the shock and reconnection processes from micro- to macroscopic scales. These can now address the question of supra-thermal particle injection in non-relativistic and relativistic flows as well as the question of the origin of the most energetic cosmic rays. To this aspect the next generation of space (like SVOM) or ground- based (like CTA) instruments will bring additional constraints on the accelerators. The workshop ‘Particle acceleration in astrophysical and space plasmas’ proposed for the SF2A 2019 aims at bringing together the heliosphysics and astrophysics communities to present the most recent observational and theoretical results in the field of particle acceleration. The idea for this session stems from the realisation that both communities face similar challenges: • the wide range of spatial and energy scales that must be considered to model some of the acceleration processes self-consistently, these include coupling models capable of capturing fluid and kinetic scales, • the exploitation of sometimes similar remote-sensing instrumentation, for instance FERMI-GBM and LAT measurements of hard X-rays and gamma rays developed for astrophysics have become very important sources of measurements in solar physics, • the scarcity of certain critical measurements that have to be compensated by sometimes strong assumptions. To take an example, testing the theory of diffusive-shock acceleration requires assumptions on the presence or not of non- thermal tails acting as ‘seed particles’ in the acceleration process, the properties of shock waves (geometry and strength) are also critical parameters invoked to explain the variability of non-thermal emissions over extended shock regions. These are common problems encountered in both heliophysics and astrophysics. We believe that bringing the community of scientists working in France on the broad topic of particle acceleration in natural plasmas will produce new synergies.


Après midi du 15 Mai (2pm-6pm, salle 2)
2:00-2:30pm Martin Lemoine (IAP): Particle acceleration in relativistic outflows
2:30-3:00pm Nicole Vilmer (LESIA): Accélération de particules dans la couronne solaire PDF presentation
3:00-3:30pm Alexandre Marcowith (LUPM): Non-thermal particle acceleration in young stellar objects
3:30-3:50pm Rolf Walder (CRAL): Particle Acceleration by relativistic magnetic reconnection
3:50-4:10pm Coffee Break
4:10-4:30pm Gwenael Giacinti (MPIK): Electron Acceleration in the Crab Nebula PDF presentation
4:30-4:50pm Athanasios Kouloumvakos (IRAP): Shock waves properties in the solar corona and their relation to solar energetic particles
4:50-5:10pm Olivier Hervet (UCSC): Signatures of recollimation shocks in blazars, focus on Mrk 421 PDF presentation
5:10-5:30pm Olivier Le Contel (LPP): Interactions ondes/particules, accélération et structures non linéaires associées aux jets de plasmas se propageant dans la queue géomagnétique
5:30-5:50pm Karl-Ludwig Klein (LESIA): Observation of particle acceleration in the solar corona with neutron monitors and radio instruments PDF presentation

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