Extended Gamma-Ray Emissions and Cosmic-Ray Anisotropy as Novel Probes of the Interstellar Turbulence
by
DrGwenael Giacinti(Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg)
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Asia/Shanghai
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Description
Abstract
Pulsar wind nebulae (PWNe) accelerate electrons to very high energies (VHE), but the acceleration mechanism and site remain uncertain. We study particle acceleration at a pulsar wind termination shock by integrating trajectories in a model of the magnetic field and flow pattern inspired by MHD simulations. We find that drift motion along the shock surface keeps either electrons or positrons in a ring-shaped region close to the equatorial plane of the pulsar, where they are accelerated by the first-order Fermi process.
Old pulsars and PWNe eventually leave their supernova remnants, and their VHE electrons may escape into the surrounding interstellar medium (ISM), creating extended ~10 TeV gamma-ray emissions. Such "TeV halos" have been detected by HAWC around Geminga and Monogem, and LHAASO should detect more. We show that TeV halos can be used as novel probes of the interstellar turbulence, because electron propagation in the ISM contains information about the magnetic fields on which they scatter. We find that HAWC measurements are compatible with Kolmogorov or Kraichnan turbulence with strength B_rms ≈ 3 μG and coherence length L_c ≲ 5 pc.
Finally, we demonstrate that the TeV cosmic-ray anisotropy can be used as another probe of the interstellar turbulence. We relate its shape to the properties of the turbulence within ~10 pc from Earth, and find that IceCube and IceTop data already rule out a range of turbulence models. The 400 TeV and 2 PeV data sets of IceTop can be fitted with a Goldreich-Sridhar model that contains a smooth deficit of parallel-propagating waves. Isotropic fast magnetosonic waves can also match the observations at 2 PeV.
Biography
Dr. Giacinti studied at the Ecole Normale Superieure of Lyon, in France, and earned his Ph.D. degree from Paris 7 University. From 2012 to 2015, he worked as a postdoctoral researcher at the University of Oxford, in the United Kingdom. He now works as a postdoctoral researcher at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, Germany.
Dr. Giacinti is interested in a number of topics in theoretical high-energy astrophysics and particle astrophysics. He has worked on cosmic-ray propagation, particle acceleration in pulsar wind nebulae, supernovae and supernova remnants, as well as gamma-ray and neutrino astronomy. He is also interested in related plasma astrophysics problems, such as shock physics in the context of supernova shock breakout. In addition to his theoretical works, he is a member of the High Altitude Water Cherenkov (HAWC) and Southern Wide field-of-view Gamma-ray Observatory (SWGO) Collaborations. He is currently the science working group coordinator of SWGO.
