Nature of donors in ultra-luminous X-ray binaries powered by neutron stars

Abstract

In this study, we examine the properties of donor stars of the three recently discovered ultraluminous X-ray sources (ULXs) powered by rotating neutron stars. For this purpose, we constructed a theoretical relation between the X-ray luminosity ($L_{\mathrm{X}}$) and the orbital period ($P_{\mathrm{orb}}$) suitable for ULXs with neutron stars. By using this new $L_{\mathrm{X}}-P_{\mathrm{orb}}$ relation, we attempt to determine the currently unknown nature of donor stars in ULXs associated with neutron stars. Especially, comparing the observed properties with the stellar evolution tracks, we suggest that the donor star in the NGC5907 ULX-1 system is a moderately massive star with $6-12{\mathrm{M}}_{\odot }$, 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 seems to involve relatively massive donors.

7 pages, 4 figures, 4 tables. Accepted for publication in MNRAS

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Cited by in corpus (2)

• Exploring the nature of ultra-luminous X-ray sources across stellar population ages using detailed binary evolution calculations
• X-ray irradiation of the stellar wind in HMXBs with B supergiants: Implications for ULXs