LOFAR Discovery of the Fastest-spinning Millisecond Pulsar in the Galactic Field

C. G. Bassa, Z. Pleunis, J. W. T. Hessels, E. C. Ferrara, R. P. Breton, N. V. Gusinskaia, V. I. Kondratiev, S. Sanidas, L. Nieder, C. J. Clark, T. Li, A. S. Van Amesfoort, T. H. Burnett, F. Camilo, P. F. Michelson, S. M. Ransom, P. S. Ray, K. Wood

    Research output: Contribution to journalArticlepeer-review

    Abstract

    We report the discovery of PSR J0952−0607, a 707 Hz binary millisecond pulsar that 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 γ-ray sources. PSR J0952−0607 is in a 6.42 hr orbit around a very low-mass companion (Mc  0.02 M), 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¢ = 22.2 at maximum to r¢ > 23.8, indicating that it is irradiated by the pulsar wind. Swift observations place a 3σ upper limit on the 0.3 10 ke - V X-ray luminosity of LX < ´ 1.1 1031 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 a ~ -3 (where µ na S ). 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.
    Original languageEnglish
    Pages (from-to)L20
    JournalThe Astrophysical Journal Letters
    Volume846
    Issue number2
    DOIs
    Publication statusPublished - 5 Sept 2017

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