Searching for pulsars associated with polarised point sources using LOFAR: Initial discoveries from the TULIPP project

¹ CSIRO Space and Astronomy, PO Box 1130, Bentley, WA 6102, Australia
e-mail: sobey.charlotte@gmail.com
² ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
e-mail: bassa@astron.nl
³ School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, D09 W6Y4 Glasnevin, Ireland
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada
⁶ McGill Space Institute, McGill University, 3550 rue University, Montréal, QC H3A 2A7, Canada
⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁸ Astro Space Centre, Lebedev Physical Institute, Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
⁹ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
¹⁰ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
¹¹ INAF Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
¹² LPC2E – Université d’Orléans / CNRS, France
¹³ Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 – Univ. Orléans, OSUC, 18330 Nançay, France
¹⁴ Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, Nijmegen 6500 GL, The Netherlands
¹⁵ Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK

Received: 9 November 2021
Accepted: 9 February 2022

Abstract

Discovering radio pulsars, particularly millisecond pulsars (MSPs), is important for a range of astrophysical applications, such as testing theories of gravity or probing the magneto-ionic interstellar medium. We aim to discover pulsars that may have been missed in previous pulsar searches by leveraging known pulsar observables (primarily polarisation) in the sensitive, low-frequency radio images from the Low-Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS), and have commenced the Targeted search, using LoTSS images, for polarised pulsars (TULIPP) survey. For this survey, we identified linearly and circularly polarised point sources with flux densities brighter than 2 mJy in LoTSS images at a centre frequency of 144 MHz with a 48 MHz bandwidth. Over 40 known pulsars, half of which are MSPs, were detected as polarised sources in the LoTSS images and excluded from the survey. We have obtained beam-formed LOFAR observations of 30 candidates, which were searched for pulsations using coherent de-dispersion. Here, we present the results of the first year of the TULIPP survey. We discovered two pulsars, PSRs J1049+5822 and J1602+3901, with rotational periods of P = 0.73 s and 3.7 ms, respectively. We also detected a further five known pulsars (two slowly-rotating pulsars and three MSPs) for which accurate sky positions were not available to allow a unique cross-match with LoTSS sources. This targeted survey presents a relatively efficient method by which pulsars, particularly MSPs, may be discovered using the flexible observing modes of sensitive radio telescopes such as the Square Kilometre Array and its pathfinders/precursors, particularly since wide-area all-sky surveys using coherent de-dispersion are currently computationally infeasible.