Dipanjan Mitra

Pulsars are highly magnetized fast rotating neutron stars (a highly dense star with a radius of about 10 km comprising mostly of neutrons), capable of emitting beams of electromagnetic radiation. As the beam crosses the observer in the earth a pulse of emission is seen. The pulsar taps its own rotational energy to produce the EM radiation which is seen across the electromagnetic spectrum from radio to gamma rays. However, we do not know how the strong electric and magnetic field are oriented around the neutron star and how they accelerate charged particles to generate the radiation. The physical mechanism of how pulsars shine is still unknown, even after 45 years of its discovery and is one of the most challenging problems in astrophysics.


My research focuses on understanding the radio emission mechanism in pulsars. The Radio emission forms a tiny fraction of the total energy released by pulsars during spin down. The majority of this energy is lost as high-energy X-ray and gamma-ray radiation and as a wind of relativistically charged particles flowing out into the ambient interstellar medium. The radio emission however is unique as it has a very high brightness temperatures (or an equivalent blackbody temperature of a thermal source) of about 1027 K. The extreme nature of the emission is apparent when one realizes that a spatial region of only about 500 meters is capable of generating emission having such high equivalent blackbody temperature (one can compare this with the Sun which is a 5780 K blackbody and has a radius of 695,500 km). The pulsar radio emission hence has a non-thermal origin and is commonly termed as a coherent emission mechanism. The emission is generated in regions of ultra-strong magnetic and electric fields where energetic photons split into an electron and positron pair through a process of magnetic pair creation and can be accelerated to relativistic speeds. It is believed that growth of plasma instabilities in the electron-positron plasma leads to the pulsar radio emission, although a self-consistent theory is yet to be found.


My research comprises of observational, phenomenological and theoretical studies that assist to unravel the coherent emission mechanism in pulsars (Refer to this article for open problems that I am interested in pulsars: http://arxiv.org/pdf/1304.1980v1.pdf) More specifically the area of my study includes:


(1) Use of radio observatories like GMRT, Arecibo, WSRT, LOFAR etc to study radio emission properties such as pulsar polarization, off-pulse emission, pulsar drifting, modeling, nulling. In-depth understanding of these properties provides a constraint to the pulsar emission theories.

(2) Use of simultaneous X-ray (using XMM satellite) and radio studies to understand the global structure of the pulsar magnetosphere.

(3) Understanding theoretically how plasma waves are genee and propagate in the pulsar magnetosphere.

My additional research interests include understanding the ISM using pulsar and probes and studying cosmic ray propagation process in grand design spiral galaxies.


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