MR. YOGESH MANN

The origin of two distinct conal emission zones in pulsars, i.e., the "outer" and the "inner" emission cones, as well as the marked differences in observed spectral properties of the respective emission components, remains poorly understood. The sub-pulse modulation in the corresponding conal components, if mapped back to the underlying system of sub-beams rotating around the magnetic axis (as envisioned by Ruderman and Sutherland; 1975), provides a potential way to investigate the emission morphologies in the two conal regions, and more importantly, any inter-relationship between them. Using our analysis on a number of pulse-sequences of the bright pulsar B1237+25 at 327 MHz, we present evidences supporting the view that the two cones of this pulsar (the outer and the inner cone) originate from a common system of sub-beams, but at two distinct emission altitudes. We also see indications of a twist in the emission columns, most likely associated with a corresponding twist in the magnetic field structure of this pulsar. Further investigations using simultaneous multi-frequency observations could provide crucial clues about the physical processes responsible for emission in the inner cone. A self-contained multi-band receiver system was designed and developed at the Raman Research Institute, specially for such tomographic studies of the pulsar polar emission regions. The speaker would also briefly describe this system, and present synoptic results obtained from the observations carried out with the Green Bank Telescope using this receiver.