Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR^⋆

¹ ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
e-mail: pilia@astron.nl
² INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius ( CA), Italy
³ Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
⁴ Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
⁵ Astro Space Center of the Lebedev Physical Institute, Profsoyuznaya str. 84/32, 117997 Moscow, Russia
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁸ School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK
⁹ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁰ LPC2E – Universite d’Orleans/CNRS  
¹¹ Station deRadioastronomie de Nançay, Observatoire de Paris – CNRS/INSU, USR 704 – Univ. Orléans, OSUC , route de Souesmes, 18330 Nançay, France
¹² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H29, PO Box 218, VIC 3122, Australia
¹³ ARC Centre of Excellence for All-sky astrophysics (CAASTRO), Sydney Institute of Astronomy, University of Sydney, Australia
¹⁴ NAOJ Chile Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
¹⁵ Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
¹⁶ Department of Physics & Astronomy, University of the Western Cape, Private Bag X17, 7535 Bellville, South Africa
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ Helmholtz-Zentrum Potsdam, DeutschesGeoForschungsZentrum GFZ, Department 1: Geodesy and Remote Sensing, Telegrafenberg, A17, 14473 Potsdam, Germany
¹⁹ Shell Technology Center, 3333 Bangalore, India
²⁰ SRON Netherlands Insitute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
²¹ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
²² CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia
²³ University of Twente, 7522 Enschede, The Netherlands
²⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
²⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²⁶ University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
²⁷ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
²⁸ Max Planck Institute for Astrophysics, Karl Schwarzschild Str. 1, 85741 Garching, Germany
²⁹ Laboratoire AIM (CEA/IRFU – CNRS/INSU – Université Paris Diderot), CEA DSM/IRFU/SAp, 91191 Gif-sur-Yvette, France
³⁰ SmarterVision BV, Oostersingel 5, 9401 JX Assen, The Netherland
³¹ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
³² Laboratoire Lagrange, UMR 7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, 06300 Nice, France
³³ Astronomisches Institut der Ruhr-Universität Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany
³⁴ Sodankylä Geophysical Observatory, University of Oulu, Tähteläntie 62, 99600 Sodankylä, Finland
³⁵ STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK
³⁶ International Centre for Radio Astronomy Research – Curtin University, GPO Box U1987, Perth, WA 6845, Australia
³⁷ Center for Information Technology (CIT), University of Groningen, 9700 CA Groningen, The Netherlands
³⁸ Centre de Recherche Astrophysique de Lyon, Observatoire de Lyon, 9 avenue Charles André, 69561 Saint-Genis-Laval Cedex, France
³⁹ Department of Physics and Elelctronics, Rhodes University, PO Box 94, 6140 Grahamstown, South Africa
⁴⁰ SKA South Africa, 3rd Floor, The Park, Park Road, 7405 Pinelands, South Africa
⁴¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
⁴² LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France

Received: 20 October 2014
Accepted: 18 September 2015

Abstract

Context. LOFAR offers the unique capability of observing pulsars across the 10−240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively.

Aims. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium.

Methods. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120–167 MHz, 100 profiles) and low band (15–62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR.

Results. We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories.