Plasma hybrid modelling of supernova remnants shock precursors

• Applicant: Dr. Tatyana Liseykina
• Subject Area: Astrophysics and Astronomy
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 278305671

Although cosmic rays have been discovered a century ago, their origin is still not precisely known. Latest direct observations support the hypothesis that most of the galactic cosmic rays originate from galactic supernova remnants, and that the diffusive shock acceleration is the underlying acceleration mechanism. Unfortunately, the limited understanding of the confinement of energetic particles in partially ionized molecular clouds in front of the supernova remnant shocks, the modification of molecular clouds by the cosmic rays and their propagation into the interstellar medium precludes the interpretation of the observations of supernova remnants. Most notably this refers to the Fermi Large Area Telescope observations as a conclusive evidence of the supernova remnant-cosmic ray connection with the diffusive shock acceleration being the mechanism behind it. The diffusive shock acceleration is a process whereby accelerated particles drive instabilities that confine them to the shock by scattering so that they gain energy more rapidly. Moreover, the accelerated particles modify the shock structure and the acceleration becomes even more efficient. In addition, the strong cosmic ray pressure gradient and current provide new free energy sources for more instabilities in the shock precursor. The most important cosmic ray-driven precursor instabilities thus stem from the same source. Therefore, they need to be treated on an equal footing. Recent studies demonstrated that the two non-resonant precursor instabilities are coupled not only through a common energy source but also dynamically. Our specific goal in this project is to study the interaction of the non-resonant instabilities in the most interesting case of an arbitrary thermal-to-magnetic pressure ratio, as well as their dependence on the other plasma parameters. Numerically, the energetic particle dynamics and the magnetic field amplification in the shock precursor will be studied within a hybrid MHD-kinetic model, in which the kinetic modeling is restricted to the cosmic ray population. The results of these studies will allow us to calculate the modification of the spectrum from diffusive shock acceleration. Moreover, as such crucial dynamical quantities as the magnetic field amplification, plasma heating and the injection rate of cosmic rays will be self-consistently calculated, the maximum energy of cosmic rays in supernova remnants will be obtained. This quantity is essential for the comparison with observations which constrain the possible acceleration time of cosmic rays.

• DFG Programme: Research Grants