Abstract Details

Name: Minhajur Rahaman
Affiliation: NCRA-TIFR, Pune
Conference ID: ASI2020_104
Title : Langmuir instability in Pulsar Plasma
Authors and Co-Authors : Sk Minhajur Rahaman, Dipanjan Mitra, George Melikidze
Abstract Type : Poster
Abstract Category : Stars, ISM and Galaxy
Abstract : Pulsars are a class of highly magnetized (~10^8 to 10^12 gauss) and fast rotating (~ msec to sec) neutron stars giving out beamed electromagnetic radiation across the electromagnetic spectrum from radio to gamma-rays. Each time the beam crosses our line of sight we receive them as “pulses”. Radio emission from pulsars is characterized by a high brightness temperature (~10^27 K) which is at least 12 orders of magnitude higher than the incoherent synchrotron limit. This points to a highly coherent process where the emission is due to in-phase emission of a large number of particles which acts as a single entity termed the “charged bunches” rather than single-particle emission. The bunching condition requires a plasma instability in pulsar magnetosphere. The identification of the unstable plasma mode(s) that can generate pulsar radio emission has been a challenge since the discovery of pulsars. However recent observational constraints such as emission height has allowed the identification of Langmuir mode as an unique candidate. Curvature radiation due to Langmuir bunches is the most natural explanation of the pulsar radio emission. However, it will be shown that analysis in the linear regime is insufficient and a non-linear treatment of the mode is a necessity. The Langmuir bunches disperse too fast and needs high enough growth rates so that its dispersal can be arrested due to non-linear Miller force. In this talk I will present our work on three mechanisms by which Langmuir mode can be excited and estimate the growth rates in each case. The three mechanisms are the high energy beam driven instability, two stream instability due to longitudinal drift in secondary plasma and the two stream instability instability due to cloud-cloud overlap as a result of non-stationary discharges at the polar gap. Among these the cloud-cloud overlap will be shown to be the most plausible one.