LOFAR discovery of the fastest-spinning millisecond pulsar in the Galactic field

• Published in: arXiv.org 2017-09
• Main Authors: Bassa, C G, Pleunis, Z, Hessels, J W T, Ferrara, E C, Breton, R P, Gusinskaia, N V, Kondratiev, V I, Sanidas, S, Nieder, L, Clark, C J, T Li, van Amesfoort, A S, Burnett, T H, Camilo, F, Michelson, P F, Ransom, S M, Ray, P S, Wood, K
• Format: Article
• Language: English
• Subjects: Binary stars; Companion stars; Flux density; Galactic clusters; Light curve; LOFAR; Luminosity; Millisecond pulsars; Neutron flux; Neutron stars; Neutrons; Orbits; Radio spectra; Stellar winds
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1709.01453

We report the discovery of PSR J0952\(-\)0607, a 707-Hz binary millisecond pulsar which is now the fastest-spinning neutron star known in the Galactic field (i.e., outside of a globular cluster). PSR J0952\(-\)0607 was found using LOFAR at a central observing frequency of 135 MHz, well below the 300 MHz to 3 GHz frequencies typically used in pulsar searches. The discovery is part of an ongoing LOFAR survey targeting unassociated Fermi Large Area Telescope \(\gamma\)-ray sources. PSR J0952\(-\)0607 is in a 6.42-hr orbit around a very low-mass companion (\(M_\mathrm{c}\gtrsim0.02\) M\(_\odot\)) and we identify a strongly variable optical source, modulated at the orbital period of the pulsar, as the binary companion. The light curve of the companion varies by 1.6 mag from \(r^\prime=22.2\) at maximum to \(r^\prime>23.8\), indicating that it is irradiated by the pulsar wind. Swift observations place a 3-\(\sigma\) upper limit on the \(0.3-10\) keV X-ray luminosity of \(L_X < 1.1 \times 10^{31}\) erg s\(^{-1}\) (using the 0.97 kpc distance inferred from the dispersion measure). Though no eclipses of the radio pulsar are observed, the properties of the system classify it as a black widow binary. The radio pulsed spectrum of PSR J0952\(-\)0607, as determined through flux density measurements at 150 and 350 MHz, is extremely steep with \(\alpha\sim-3\) (where \(S \propto \nu^{\alpha}\)). We discuss the growing evidence that the fastest-spinning radio pulsars have exceptionally steep radio spectra, as well as the prospects for finding more sources like PSR J0952\(-\)0607.