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

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.

The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2

“…Sobey et al 2019). We found 25 pulsars in the DR2 area, 24 of which were previously known, with one being a new discovery, which is described in Sobey et al (2022). The 25 pulsars are listed in Table B1, providing new high precision RMs and positions.…”

A Green Bank Telescope Search for Narrowband Technosignatures between 1.1 and 1.9 GHz During 12 Kepler Planetary Transits

“…Another way to address high-drift signals is to coherently correct the raw voltage data to an accelerating reference frame or fiducial drift rate (e.g., ±100 Hz s −1 ) before the creation of the reduced and channelized data products (as done in pulsar dedispersion; e.g., Sobey et al 2022). For signals at the chosen drift rate, there will be no sensitivity loss, and signals that are nearby in drift-rate space can be searched for incoherently (with the same sensitivity loss considerations as discussed above), broadening the applicability of the technique.…”

Image-based searches for pulsar candidates using MWA VCS data

“…MWA surveys of linearly polarised sources and pulsar searches were also conducted by Riseley et al (2018Riseley et al ( , 2020. Several other surveys are currently ongoing, such as a search for pulsars associated with polarised point sources using LOFAR, which detected 2 new pulsars (Sobey et al 2022) and a circular polarisation survey for radio stars with the ASKAP, resulting in 37 pulsar detections, despite them only looking for flare stars (Pritchard et al 2021).…”