The Origin of the Ultraluminous X-Ray Sources
Abstract
Recently, several ultraluminous X-ray (ULX) sources were shown to host a neutron star (NS) accretor. We perform a suite of evolutionary calculations, which show that, in fact, NSs are the dominant type of ULX accretor. Although black holes (BH) dominate early epochs after the star-formation burst, NSs outweigh them after a few 100 Myr and may appear as late as a few gigayears after the end of the star-formation episode. If star formation is a prolonged and continuous event (I.e., not a relatively short burst), NS accretors dominate the ULX population at any time in the solar metallicity environment, whereas BH accretors dominate when the metallicity is sub-solar. Our results show a very clear (and testable) relation between the companion/donor evolutionary stage and the age of the system. A typical NSULX consists of a ∼ 1.3 {M}⊙ NS and ∼ 1.0 {M}⊙ Red Giant. A typical BH ULX consists of a ∼ 8 {M}⊙ BH and ∼ 6 {M}⊙ main-sequence star. Additionally, we find that the very luminous ULXs ({L}X≳ {10}41 erg s-1) are predominantly BH systems (∼ 9 {M}⊙ ) with Hertzsprung-gap donors (∼ 2 {M}⊙ ). Nevertheless, some NSULX systems may also reach extremely high X-ray luminosities (≳1041 erg s-1).
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2017
- DOI:
- 10.3847/1538-4357/aa821d
- arXiv:
- arXiv:1705.06155
- Bibcode:
- 2017ApJ...846...17W
- Keywords:
-
- methods: statistical;
- stars: black holes;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 pages, 14 figures, published in ApJ