June 14-17, 2016
Associated publication: Modelling Pulsar Wind Nebulae, Springer Astrophysics and Space Science Library, D. F. Torres (Ed.), Format: book, hardcover, Springer, ISBN 978-3-319-63030-4, 2018, 313 pages.
During the last few years, significant progress on the study of pulsar wind nebuale (PWNe) has been attained both from a theoretical and an observational perspective, focusing on the closest, more energetic, and best studied nebula: the Crab. On the one hand, what was known as the sigma problem (how the nebula magnetization evolves with distance from the pulsar, starting from being Poynting dominated to becoming particle dominated) has been studied in detail (and solved) using precise three dimensional (3D) relativistic MHD simulations. On the other hand, observations of Crab nebula with the Fermi and AGILE satellites have unexpectedly shown the appearance of flares of short duration. The high-energy emission from this source suggests that acceleration of particles up to PeV energies is possible on timescales of ~10 hr, with transient emission briefly dominating the flux, likely linked to reconnection events. The detailed study of the Crab nebula is however far from what is the usual lore in the field.
Now, the number of TeV detected PWNe (~30), mostly contributed by the H.E.S.S. survey of the Galactic plane, is similar to the number of characterized nebulae observed at other frequencies over decades of observations. But in just a few years, the Cherenkov Telescope Array will increase this number to several hundreds, actually providing an essentially complete account of TeV emitting PWNe in the Galaxy. At the other end of the multi-frequency spectrum, the SKA and its pathfinder instruments, will reveal thousands of new pulsars, and map in exquisite detail the radiation surrounding them for several hundreds of nebulae. X-ray missions currently under analysis, like Athena, and others, will also reveal currently unknown nebulae, as well as details of the bright ones in their corresponding energy regimes.
Assuming that the PWN is maintained solely by the pulsar rotational power, the gamma-ray luminosity detected is believed to be the result of Comptonization of soft photon fields by relativistic electrons injected by the pulsar during its lifetime. This scenario can lead to TeV sources without lower energy counterparts, when the synchrotron emission is reduced by the decay of the magnetic field. Also, it can lead to large mismatches in extension between gamma and X-ray energies, when the magnetic field is low enough that electrons emitting keV photons actually cool faster and are more energetic than electrons emitting in the TeV range. The explanation of these basic observational properties of PWNe does not imply that we understand the population detected in detail, nor that our models handle both multi-frequency morphology and radiation, nor that they are versatile enough to quickly apply them to hundreds of sources. Discussing how we achieve these more advanced models will be the aim of the workshop.
Elena Amato (INAF/Obs. Arcetri, Italy), Aya Bamba (Aoyama University, Japan), Emma de Oña Wilhelmi (CSIC-IEEC, Spain), Joseph Gelfand (NYUAD, United Arab Emirates), Simon Johnston (CSIRO, Australia), Serguei Komissarov (Leeds, UK), Anatoly Spitkovsky (Princeton, USA), Diego F. Torres (ICREA/CSIC-IEEC, Spain, chair)