A census of the pulsar population observed with the international LOFAR station FR606 at low frequencies (25–80 MHz)^⋆

¹ LPC2E – Université d’Orléans / CNRS, Orléans, France
e-mail: louis.bondonneau@cnrs-orleans.fr
² Station de Radioastronomie de Nançay, Observatoire de Paris – CNRS/INSU, USR 704 – Univ. Orléans, OSUC, Route de Souesmes, 18330 Nançay, France
³ Laboratoire Univers et Théories LUTh, Observatoire de Paris, CNRS/INSU, Université Paris Diderot, 5 Place Jules Janssen, 92190 Meudon, France
⁴ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 Amsterdam, The Netherlands
⁵ ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 Dwingeloo, The Netherlands
⁶ Astro Space Center, Lebedev Physical Institute, Russian Academy of Sciences, Profsoyuznaya Str. 84/32, 117977 Moscow, Russia
⁷ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, 7925 Cape Town, South Africa
⁸ Department of Physics and Astronomy, University of the Western Cape, 7535 Cape Town, South Africa
⁹ Department of Physics and Astronomy, Jodrell Bank Centre for Astrophysics, The University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK

Received: 2 October 2019
Accepted: 28 November 2019

Abstract

Context. To date, only 69 pulsars have been identified with a detected pulsed radio emission below 100 MHz. A LOFAR-core LBA census and a dedicated campaign with the Nançay LOFAR station in stand-alone mode were carried out in the years 2014–2017 in order to extend the known population in this frequency range.

Aims. In this paper, we aim to extend the sample of known radio pulsars at low frequencies and to produce a catalogue in the frequency range of 25–80 MHz. This will allow future studies to probe the local Galactic pulsar population, in addition to helping explain their emission mechanism, better characterising the low-frequency turnover in their spectra, and obtaining new information about the interstellar medium through the study of dispersion, scattering, and scintillation.

Methods. We observed 102 pulsars that are known to emit radio pulses below 200 MHz and with declination above −30°. We used the Low Band Antennas (LBA) of the LOw Frequency ARray (LOFAR) international station FR606 at the Nançay Radio Observatory in stand-alone mode, recording data between 25 and 80 MHz.

Results. Out of our sample of 102 pulsars, we detected 64. We confirmed the existence of ten pulsars detected below 100 MHz by the LOFAR LBA census for the first time (Bilous et al. 2020, A&A, 635, A75) and we added two more pulsars that had never before been detected in this frequency range. We provided average pulse profiles, DM values, and mean flux densities (or upper limits in the case of non-detections). The comparison with previously published results allows us to identify a hitherto unknown spectral turnover for five pulsars, confirming the expectation that spectral turnovers are a widespread phenomenon.