Joeri van Leeuwen (Astronomical Institute, Utrecht University)

Probing the nulling and subpulse-drifting mechanisms in radio pulsars - Joeri van Leeuwen Colloquium

ATNF Marsfield Lecture Theatre

Abstract

Both nulling (a sudden temporary stop of pulsar emission) and subpulse
drifting (a striking second periodicity in the pulsar signal) are
poorly understood phenomena. We probe their mechanisms by
investigating how they interact in PSR B0809+74. We solve the subpulse
alias order problem and find that one spark makes one driftband. From
this we derive a subbeam-carousel rotation time of more than 200
seconds, much longer than predicted by theory.

We find that after nulls the drift-pattern is changed and that it can
remain stably different for about 150 seconds. With the alias mode
known, we can now tie these drift-pattern changes to changes in
emission-region geometry. We show that post-null emission originates
deeper in the pulsar magnetosphere. Both this emission-height change
and the striking increase in carousel-rotation time can be explained
by a post-null decrease in gap height. This offers a glance at the
circumstances needed to make the pulsar turn off so dramatically.