Probable Dormant Neutron Star in a Short-Period Binary System

• DOI: 10.48550/arxiv.2206.11270
• Publication Date: 2022-01-01
• Authors: T. Mazeh; S. Faigler; Dolev Bashi; S. Shahaf; Niv Davidson; Matthew Green; Roy Gomel; Dan Maoz; Amitay Sussholz; Subo Dong; Haotong Zhang; Jifeng Liu; Song Wang; A-Li Luo; Zheng Zheng; Na’ama Hallakoun; V. Perdelwitz; David W. Latham; I. Ribas; D. Baroch; J. C. Morales; E. Nagel; N. C. Santos; David R. Ciardi; Jessie L. Christi...; Michael B. Lund; Joshua N. Winn
• Keywords: Orbital period; X-ray binary

We have identified 2XMM J125556.57+565846.4, at a distance of 600 pc, as binary system consisting normal star and probable dormant neutron star. Optical spectra exhibit slightly evolved F-type single star, displaying periodic Doppler shifts with 2.76-day Keplerian circular orbit, no indication light from secondary component. UV photometry reveal ellipsoidal variations half the orbital period, due to tidal deformation F The mass unseen companion is constrained range $1.1$--$2.1\,M_{\odot}$ $3σ$ confidence, median distribution $1.4\,M_{\odot}$, typical known stars. A main-sequence cannot masquerade dark companion. possible masses still allows for possibility very massive white dwarf. itself could also be close pair dwarf an M or two dwarfs, although evolution that would lead such triple unlikely. Similar ambiguities regarding certain identification are bound affect most future discoveries this type non-interacting system. If indeed contains it will become, in future, bright X-ray source afterwards might even host millisecond pulsar.