Le 24 mai 2019
De 10h30 à 12h00
Dipanjan Mitra
National Centre for Radio Astrophysics, Tata Institute of Fundamental Research
Collective plasma emissions in astrophysics are referred to as coherent emission. Radio emission from pulsars are coherent in nature,and observations strongly suggest that: (a) the coherent emission is excited by acceleration of « charge bunches » in a 1D relativisticallymoving pair plasma, and (b) the radio emission occurs at a frequencylower than the local plasma frequency. Theoretically, it is challenging to form a stable charge bunch that follow the above observational constraints, and even after fifty years of pulsar discovery the mechanism of how collective plasma process excites the coherent radio emission remains an unresolved problem.
In this talk we will propose a potential resolution for the formation of charge bunches, based on a kinetic theory of linear and non-linear growth of electrostatic Langmuir waves in the relativistic pair plasma. In the non-linear regime, we will demonstrate the existence of relativistic charge solitons (the “charge bunches”) as solutions of the non-linear Schrodinger equation (NLSE). The formalism includes the crucial effect of non-linear Landau damping, which is inherent in the derivation of the NLSE. We will also demonstrate a remarkable finding, i.e. the emergence of these intense soliton-like pulses from an initial disordered state of Langmuir waves.