Probing drifting and nulling mechanisms through their interaction in PSR B0809+74

¹ Astronomical Institute, Utrecht University, PO Box 80000, 3508 TA Utrecht, The Netherlands
² Stichting ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands
³ Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁴ Physics Department, University of Vermont, Burlington, VT 05405, USA

Corresponding author: Joeri van Leeuwen, jleeuwen@astro.uu.nl More information: http://www.astro.uu.nl/~jleeuwen/

Received: 1 July 2002
Accepted: 5 November 2002

Abstract

Both nulling and subpulse drifting are poorly understood phenomena. We probe their mechanisms by investigating how they interact in PSR B0809+74. We find that the subpulse drift is not aliased but directly reflects the actual motion of the subbeams. The carousel-rotation time must then be over 200 s, which is much longer than theoretically predicted.
The drift pattern after nulls differs from the normal one, and using the absence of aliasing we determine the underlying changes in the subbeam-carousel geometry. We show that after nulls, the subbeam carousel is smaller, suggesting that we look deeper in the pulsar magnetosphere than we do normally. The many striking similarities with emission at higher frequencies, thought to be emitted lower too, confirm this. The emission-height change as well as the striking increase in carousel-rotation time can be explained by a post-null decrease in the polar gap height. This offers a glimpse of the circumstances needed to make the pulsar turn off so dramatically.