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Volume 387, Number 1, May III 2002
Page(s) 169 - 178
Section Formation, structure and evolution of stars

A&A 387, 169-178 (2002)
DOI: 10.1051/0004-6361:20020254

Null-induced mode changes in PSR B0809+74

A. G. J. van Leeuwen1, M. L. A. Kouwenhoven1, R. Ramachandran2, 3, J. M. Rankin2, 4 and B. W. Stappers3

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

(Received 17 December 2001 / Accepted 14 February 2002 )

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.

Key words: stars: neutron -- pulsars: general -- pulsars: individual: PSR B0809+74

Offprint request: A. G. J. van Leeuwen,

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