Issue |
A&A
Volume 572, December 2014
|
|
---|---|---|
Article Number | A52 | |
Number of page(s) | 14 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/201424425 | |
Published online | 27 November 2014 |
LOFAR observations of PSR B0943+10: profile evolution and discovery of a systematically changing profile delay in bright mode
1
Department of Astrophysics/IMAPPRadboud University Nijmegen,
PO Box 9010,
6500 GL
Nijmegen,
The Netherlands
e-mail:
a.bilous@science.ru.nl
2
ASTRON, the Netherlands Institute for Radio
Astronomy, Postbus
2, 7990 AA,
Dwingeloo, The
Netherlands
3
Anton Pannekoek Institute for Astronomy, University of
Amsterdam, Science Park
904, 1098 XH
Amsterdam, The
Netherlands
4
Jodrell Bank Centre for Astrophysics, School of Physics and
Astronomy, University of Manchester, Manchester
M13 9PL,
UK
5
School of Physics and Astronomy, University of
Southampton, Southampton, SO17
1BJ, UK
6
Astro Space Centre of the Lebedev Physical
Institute, Profsoyuznaya str.
84/32, 117997
Moscow,
Russia
7
Centre for Astrophysics and Supercomputing, Swinburne University
of Technology, Mail H30, PO Box
218, VIC
3122,
Australia
8
ARC Centre of Excellence for All-sky Astrophysics (CAASTRO)
9
MPI für Radioastronomy, Auf dem Hügel 69,
53121
Bonn,
Germany
10
LPC2E - Université d’Orléans/CNRS,
France
11
SR de Nançay, Observatoire de Paris – CNRS/INSU, USR 704 – Univ. Orléans, OSUC,
route de
Souesmes, 18330
Nançay,
France
12
Department of Astrophysics, University of Oxford,
Denys Wilkinson Building, Keble
Road, Oxford
OX1 3RH,
UK
Received: 18 June 2014
Accepted: 29 August 2014
We present broadband, low-frequency (25−80 MHz and 110−190 MHz) LOFAR observations of PSR B0943+10, with the goal of better illuminating the nature of its enigmatic mode-switching behaviour. This pulsar shows two relatively stable states: a “bright” (B) and “quiet” (Q) mode, each with different characteristic brightness, profile morphology, and single-pulse properties. We model the average profile evolution both in frequency and time from the onset of each mode, and highlight the differences between the two modes. In both modes, the profile evolution can be explained well by radius-to-frequency mapping at altitudes within a few hundred kilometres of the stellar surface. If both B and Q-mode emissions originate at the same magnetic latitude, then we find that the change of emission height between the modes is less than 6%. We also find that, during B-mode, the average profile is gradually shifting towards later spin phase and then resets its position at the next Q-to-B transition. The observed B-mode profile delay is frequency-independent (at least from 25−80 MHz) and asymptotically changes towards a stable value of about 4 × 10-3 in spin phase by the end of mode instance, so much too high to be due to a changing spin-down rate. Such a delay can be interpreted as a gradual movement of the emission cone against the pulsar’s direction of rotation, with different field lines being illuminated over time. Another interesting explanation is a possible variation in the accelerating potential inside the polar gap. This explanation connects the observed profile delay to the gradually evolving subpulse drift rate, which depends on the gradient of the potential across the field lines.
Key words: pulsars: general / pulsars: individual: PSR B0943+10
© ESO, 2014
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