Gated interferometric imaging of pulsars to detect off-pulse emission

Abstract

We detected off-pulse emission from two pulsars, B0525+21 and B204516, at 325 MHz using the Giant Metrewave radio telescope. Using the instrument as a high time resolution interferometer and off-line gating we imaged the off-pulse and on-pulse sections of the pulsar period separately to detect off-pulse emission at the level of a few percent of the on-pulse emission. These long period pulsars with low spin-down energies were selected to minimise the detection of emission from pulsar wind nebula. Indeed, interpreting our observation in terms of wind nebulae requires very anomalous interstellar medium particle densities. The alternative explanation of magnetospheric emission poses interesting questions to pulsar emission models. We are in the process of repeating the observations with a larger sample of pulsars and at other frequencies to obtain the spectral index, which is expected to provide further diagnostics for the nature of this emission. These are perhaps the first secure detections of off-pulse emission from pulsar magnetospheres and the first use of GMRT as a gated interferometer to image pulsars.