Understanding the radio emission geometry of PSR B0329+54

We have analyzed high-quality single-pulse data of PSR B0329+54 at 325 and 606 MHz to study the structure of the emission beam. Using the "window-threshold technique," which is suitable for detecting weak emission components, we have detected four additional emission components in the pulse window. Three of these are new components, and the fourth is a confirmation of a recently proposed component. Hence, PSR B0329+54 is now known to have nine emission components-the highest among all known pulsars. The distribution of the pulse components around the central core component indicates that the emission beam consists of four nested cones. The asymmetry in the location of the conal components in the leading versus trailing parts of the profile is interpreted as being due to aberration and retardation in the pulsar magnetosphere. These measurements allow us to determine the precise location of the four conal rings of emission. We find that the successive outer cones are emitted at higher altitudes in the magnetosphere. Furthermore, for any given cone, the emission height at the lower frequency is found to be more than that at the higher frequency. The inferred heights range from similar to 160 to similar to 1150 km. The set of "active" field lines, from which most of the conal radiation appears to originate, is found to be confined to a region located within similar to0.5-similar to0.6 of the polar cap radius. We discuss the implications of our new findings to our understanding of the pulsar emission geometry and its impact on the emission mechanisms.