Differential frequency-dependent delay from the pulsar magnetosphere
1
School of Physics and Astronomy, University of Southampton,
Southampton,
SO17 1BJ,
UK
e-mail:
tomehassall@gmail.com
2
Jodrell Bank Center for Astrophysics, School of Physics and
Astronomy, The University of Manchester, Manchester
M13 9PL,
UK
3
Netherlands Institute for Radio Astronomy (ASTRON),
Postbus 2, 7990 AA
Dwingeloo, The
Netherlands
4
Astronomical Institute “Anton Pannekoek”, University of
Amsterdam, Postbus
94249, 1090 GE
Amsterdam, The
Netherlands
5
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD
21218,
USA
6
Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road,
Oxford
OX1 3RH,
UK
7
Max-Planck-Institut für Radioastronomie,
Auf dem Hügel 69, 53121
Bonn,
Germany
8
Station de Radioastronomie de Nançay, Observatoire de Paris,
CNRS/INSU, 18330
Nançay,
France
9
Laboratoire de Physique et Chimie de l’Environnement et de
l’Espace, LPC2E, UMR 7328 CNRS, 45071
Orléans Cedex 02,
France
10
ARC Centre of Excellence for All-sky astrophysics (CAASTRO),
Sydney Institute of Astronomy, University of Sydney, 44 Rosehill Street Redfern, NSW
2016
Sydney,
Australia
11
Thüringer Landessternwarte, Sternwarte 5,
07778
Tautenburg,
Germany
12
Department of Astrophysics/IMAPP, Radboud University
Nijmegen, PO Box
9010, 6500 GL
Nijmegen, The
Netherlands
13
International Centre for Radio Astronomy Research – Curtin
University, GPO Box
U1987, Perth,
WA
6845,
Australia
14
Argelander-Institut für Astronomie, University of
Bonn, Auf dem Hügel
71, 53121
Bonn,
Germany
15
LESIA, UMR CNRS 8109, Observatoire de Paris,
92195
Meudon,
France
16
Onsala Space Observatory, Dept. of Earth and Space Sciences,
Chalmers University of Technology, 43992
Onsala,
Sweden
17
Kapteyn Astronomical Institute, PO Box 800, 9700 AV
Groningen, The
Netherlands
18
Institute for Astronomy, University of Edinburgh, Royal
Observatory of Edinburgh, Blackford
Hill, Edinburgh
EH9 3HJ,
UK
19
University of Hamburg, Gojenbergsweg112, 21029
Hamburg,
Germany
20
Jacobs University Bremen, Campus Ring 1, 28759
Bremen,
Germany
21
Leibniz-Institut für Astrophysik Potsdam (AIP),
An der Sternwarte 16,
14482
Potsdam,
Germany
22
Research School of Astronomy and Astrophysics, Australian National
University, Mt Stromlo Obs., via
Cotter Road, Weston, A.C.T.
2611,
Australia
23
Max Planck Institute for Astrophysics,
Karl Schwarzschild Str. 1,
85741
Garching,
Germany
24
Laboratoire Lagrange, UMR7293, Université de Nice
Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300
Nice,
France
25
Leiden Observatory, Leiden University,
PO Box 9513, 2300 RA
Leiden, The
Netherlands
26
Astronomisches Institut der Ruhr-Universität Bochum,
Universitaetsstrasse 150, 44780
Bochum,
Germany
27
Centre de Recherche Astrophysique de Lyon, Observatoire de
Lyon, 9 Av. Charles
André, 69561
Saint Genis Laval Cedex,
France
28
Harvard-Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge,
MA
02138,
USA
Received: 19 November 2012
Accepted: 10 February 2013
Some radio pulsars show clear “drifting subpulses”, in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14–5100 MHz. Despite this, the shapes of the driftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies (<500 MHz), a discrete step of ~180° in subpulse phase is observed at higher frequencies (>820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency – one driftband arriving 30 pulses earlier at 20 MHz than it does at 1380 MHz, whilst the other arrives simultaneously at all frequencies. The drifting pattern which is observed here cannot be explained by either the rotating carousel model or the surface oscillation model, and could provide new insight into the physical processes happening within the pulsar magnetosphere.
Key words: pulsars: general / pulsars: individual: PSR B0809+74 / telescopes
© ESO, 2013