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

• Published in: Astrophysical journal. Letters Vol. 846; no. 2; p. L20
• 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., Li, T., Amesfoort, A. S. van, Burnett, T. H., Camilo, F., Michelson, P. F., Ransom, S. M., Ray, P. S., Wood, K.
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 10.09.2017; IOP Publishing
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Binary stars; Companion stars; ECLIPSE; FLUX DENSITY; Galactic clusters; Gamma ray sources; GHZ RANGE; IRRADIATION; KEV RANGE; Light curve; LOFAR; LUMINOSITY; MASS; MHZ RANGE; Millisecond pulsars; Neutron flux; NEUTRON STARS; Neutrons; ORBITS; Pulsar winds; PULSARS; pulsars: general; pulsars: individual (PSR J0952-0607); Radio spectra; SPECTRA; stars: neutron; Stellar winds; TELESCOPES; VISIBLE RADIATION; X RADIATION
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/aa8400

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 ( ), 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 at maximum to , indicating that it is irradiated by the pulsar wind. Swift observations place a 3 upper limit on the X-ray luminosity of 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 (where ). 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.