Periodic longitude-stationary non-drift emission in core-single radio pulsar B1946+35

Abstract

Radio pulsar PSR B1946+35 is a classical example of a core/cone triple pulsar where the observer's line of sight cuts the emission beam centrally. In this paper, we perform a detailed single-pulse polarimetric analysis of B1946+35 using sensitive Arecibo archival and new observations at 1.4 and 4.6 GHz to re-establish the pulsar's classification wherein a pair of inner conal ‘outriders’ surround a central core component. The new 1.4 GHz observation consisted of a long single pulse sequence (PS) of 6678 pulses, and its fluctuation spectral analysis revealed that the pulsar shows a time-varying amplitude modulation, where for a thousand periods or so, the spectra have a broad low frequency ‘red’ excess and then at intervals they suddenly exhibit highly periodic longitude-stationary modulation of both the core and conal components for several hundred periods. The fluctuations of the leading conal and the core components are in phase, while those in the trailing conal component in counterphase. These fluctuation properties are consistent with shorter PS analyses reported in an earlier study by Weltevrede, Edwards & Stappers (2006) and Weltevrede et al. (2007) as well as in our shorter PS data sets. We argue that this dual modulation of core and conal emission cannot be understood by a model where subpulse modulation is associated with the plasma |${\boldsymbol E}$| × |${\boldsymbol B}$| drift phenomenon. Rather, the effect appears to represent a kind of periodic emission-pattern change over time-scales of ∼18 s (or 25 pulsar periods), which has not been reported previously for any other pulsar.