Null-induced mode changes in PSR B0809+74

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

Corresponding author: A. G. J. van Leeuwen, a.g.j.vanleeuwen@astro.uu.nl

Received: 17 December 2001
Accepted: 14 February 2002

Abstract

We have found that there are two distinct emission modes in PSR B0809+74. Beside its normal and most common mode, the pulsar emits in a significantly different quasi-stable mode after most or possibly all nulls, occasionally for over 100 pulses. In this mode the pulsar is brighter, the subpulse separation is less, the subpulses drift more slowly and the pulse window is shifted towards earlier longitudes. We can now account for several previously unexplained phenomena associated with the nulling-drifting interaction: the unexpected brightness of the first active pulse and the low post-null driftrate. We put forward a new interpretation of the subpulse-position jump over the null, indicating that the speedup time scale of the post-null drifting is much shorter than previously thought. The speedup time scale we find is no longer discrepant with the time scales found for the subpulse-drift slowdown and the emission decay around the null.