Visweshwar Ram Marthi

Marthi's current research focus is Scintillometry, i.e. using measurements and measurables of interstellar scintillation to study the properties of the interstellar medium (ISM). One of the preferred ways of studying the ISM is to use compact background objects to study radio wave propagation through the medium, to glean its physical properties. Radio propagation through plasma induces several observable effects such as dispersion, scattering, and scintillation. Although the three effects are distinct, they are intimately linked to one another. Traditionally, pulsars have been used to observe these effects and hence study the ISM. Additionally, active galactic nuclei (AGNs), although less popular, are often used as ISM probes. With the discovery of Fast Radio Bursts (FRBs) and the explosion in their numbers, these are now being used to study not just the ISM of the Milky Way, but also the properties of the ISM of the FRB host galaxy as well as the intergalactic medium. Using scintillation to study the phenomenon itself, as well as its applications to refine other measurements (such as, e.g., precisely solving pulsar binary orbits, measuring inclination angles, physical extent of emission regions, pulse reflex motion, extreme scattering and lensing, etc.) falls under Scintillometry. Marthi's scientific interests entail developing improved instrumentation to enable novel and niche science. He is therefore also working on Very Long Baseline Interferometry (VLBI) for the GMRT. Scintillometry can benefit greatly from VLBI, in terms of measuring the interstellar Green's function along different sightlines and the scattering geometry, i.e. whether isotropic or anisotropic. A census of pulsar scintillation can help build a 3D picture of the locations of scattering screens and explore the close and often less-than-intuitive connection between dispersion, scattering, and scintillation. As a longer-term research theme, he hopes to study the tiny-scale structure of the different phases of the ISM.

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