PSR J2019+2425: A Unique Testing Ground for Binary Evolution

Abstract

If the theoretical relationship between white dwarf mass and orbital period for wide-orbit binary radio pulsars is assumed to be correct, then the neutron star mass of PSR J2019+2425 is shown to be ~1.20 M_sun. Hence the mass of the neutron star in this system prior to the mass transfer phase is expected to have been < 1.1 M_sun. Alternatively this system descends from the accretion induced collapse (AIC) of a massive white dwarf. We estimate the magnetic inclination angles of all the observed wide-orbit low-mass binary pulsars in the Galactic disk using the core-mass period relation and assuming that the spin axis of an accreting neutron star aligns with the orbital angular momentum vector in the recycling process of the pulsar. The large estimated magnetic inclination angle of PSR J2019+2425, in combination with its old age, gives for this system evidence against alignment of the magnetic field axis with the rotational spin axis. However, in the majority of the similar systems the distribution of magnetic inclination angles is concentrated toward low values (if the core-mass period relation is correct) and suggests that alignment has taken place.