PSR J1641+3627F: A Low-mass He White Dwarf Orbiting a Possible High-mass Neutron Star in the Globular Cluster M13
Mario Cadelano, Jianxing Chen, Cristina Pallanca, Alina G. Istrate, Francesco R. Ferraro, Barbara Lanzoni, Paulo C. C. Freire, Maurizio Salaris
Abstract
Abstract We report on the discovery of the companion star to the millisecond pulsar J1631+3627F in the globular cluster M13. By means of a combination of optical and near-UV high-resolution observations obtained with the Hubble Space Telescope, we identified the counterpart at the radio source position. Its location in the color–magnitude diagrams reveals that the companion star is a faint ( ) He-core white dwarf. We compared the observed companion magnitudes with those predicted by state-of-the-art binary evolution models and found out that it has a mass of , a radius of , and a surface temperature of K. Combining the companion mass with the pulsar mass function is not enough to determine the orbital inclination and the neutron star mass; however, the last two quantities become correlated: we found that either the system is observed at a low-inclination angle, or the neutron star is massive. In fact, assuming that binaries are randomly aligned with respect to the observer line of sight, there is a of probability that this system hosts a neutron star more massive than . In fact, the maximum and median mass of the neutron star, corresponding to orbital inclination angles of 90° and 60°, are and , respectively. On the other hand, also assuming an empirical neutron star mass probability distribution, we found that this system could host a neutron star with a mass of if orbiting with a low-inclination angle around 40°.