PROFESSOR DIPANJAN MITRA

A physical mechanism that can excite the coherent radio emission in pulsars is still a challenging problem in astrophysics, even after 45 years of pulsar discovery. In all models of pulsar radio emission there is general agreement that the radio emission arises due to growth of plasma instabilities in the relativistic electron positron plasma streaming along open dipolar magnetic field. Currently a wealth of high quality observations exist, which over the years have been instrumental in putting stringent constraints to the pulsar coherent radio emission models. In this talk the speaker will discuss the observational results that strongly suggests that the pulsar radio emission is excited by coherent curvature radiation. The physical process include formation of an inner acceleration region close to the neutron star surface where magnetic pair creation forms primary plasma with lorentz factors of 10^6 followed by secondary plasma with lorentz factor of about few times 10^2 due to a non-stationary sparking process. For this process to work, highly non-dipolar surface magnetic ¿eld is essential. Then, further in the radio emission region, plasma instabilities in the secondary plasma leads to the coherent curvature radiation via multi-step process exciting extraordinary (X) and ordinary (O) modes of in the plasma. This talk will also focus on the work we are doing to unravel this physical process. The speaker will also mention issues that remain to be resolved.