The nature of donors in ultraluminous X-ray binaries powered by neutron stars
Abstract
This study examines the properties of the donor stars of three recently discovered ultraluminous X-ray sources (ULXs) powered by rotating neutron stars. In order to do this, a theoretical relationship was constructed between the X-ray luminosity (LX) and the orbital period (Porb) suitable for ULXs with neutron stars. Using this new LX-Porb relationship, we attempted to determine the currently unknown nature of donor stars in ULXs associated with neutron stars. In particular, from a comparison between the observed properties and the stellar evolution tracks, we suggest that the donor star in the NGC5907 ULX-1 system is a moderately massive star of 6-12 M⊙, just departing from the main sequence phase. The results of our models for the other two ULX systems (M82 X-2 and NGC7793 P-13) are consistent with those in previous studies. Although there are only a few samples, observed ULX systems with neutron stars seem to involve relatively massive donors.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2018
- DOI:
- 10.1093/mnras/stx2998
- arXiv:
- arXiv:1711.10004
- Bibcode:
- 2018MNRAS.474.4564K
- Keywords:
-
- accretion;
- accretion discs;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 7 pages, 4 figures, 4 tables. Accepted for publication in MNRAS