Irradiated but not eclipsed, the case of PSR J0610−2100

¹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
e-mail: emma.vanderwateren@gmail.com
² Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010 6500 GL Nijmegen, The Netherlands
³ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
⁴ Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), 30167 Hannover, Germany
⁵ Leibniz Universität Hannover, 30167 Hannover, Germany
⁶ Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Université d’Orléans/CNRS, 45071 Orléans Cedex 02, France
⁷ Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, 18330 Nançay, France
⁸ Laboratoire Univers et Théories, Observatoire de Paris, Université PSLU, CNRS, 92195 Meudon Principal Cedex, France

Received: 24 November 2021
Accepted: 7 March 2022

Abstract

We report on radio timing observations of the black widow binary pulsar J0610−2100 and optical observations of its binary companion. The radio timing observations extend the timing baseline to 16 yr and reveal a marginal detection of the orbital period derivative, but they show no significant evidence of orbital variations such as those seen in other black widow pulsars. Furthermore, no eclipses are seen in the observations at observing frequencies ranging from 310 to 2700 MHz. The optical VRI light curves were modulated with the orbital period, reaching maximum brightness of V = 26.8, R = 25.4, and I = 23.8 at superior conjunction of the companion, confirming irradiation of the companion by the pulsar. Modelling the light curves indicates that the companion is likely not filling its Roche lobe, while having a moderate inclination (i >  54°). We find an unusually low temperature and a low irradiation for the irradiated hemisphere of the companion. We investigate the absence of radio eclipses in PSR J0610−2100 and in other black widow systems in relation to their binary, pulsar, and companion properties. We also discuss the suitability of PSR J0610−2100 for pulsar timing array observations aimed at detecting nano-Hertz gravitational waves.