Radio pulsations from the γ-ray millisecond pulsar PSR J2039-5617
Abstract
The predicted nature of the candidate redback pulsar 3FGL\,J2039.6-5618 was recently confirmed by the discovery of γ-ray millisecond pulsations (Clark et al. 2020, hereafter Paper\,I), which identify this γ-ray source as . We observed this object with the Parkes radio telescope in 2016 and 2019. We detect radio pulsations at 1.4\,GHz and 3.1\,GHz, at the 2.6ms period discovered in γ-rays, and also at 0.7\,GHz in one 2015 archival observation. In all bands, the radio pulse profile is characterised by a single relatively broad peak which leads the main γ-ray peak. At 1.4\,GHz we found clear evidence of eclipses of the radio signal for about half of the orbit, a characteristic phenomenon in redback systems, which we associate with the presence of intra-binary gas. From the dispersion measure of 24.570.03\,pc\,cm-3 we derive a pulsar distance of 0.9 0.2\,kpc or 1.70.7\,kpc, depending on the assumed Galactic electron density model. The modelling of the radio and γ-ray light curves leads to an independent determination of the orbital inclination, and to a determination of the pulsar mass, qualitatively consistent to the results in Paper\,I.