The nature 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 Gyr 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 ULX population at any time in 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 NS ULX consists of a ∼1.3 M_⊙ NS and ∼1.0 M_⊙ Red Giant. A typical BH ULX consist 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) are predominantly BH systems (∼9 M_⊙) with Hertzsprung gap donors (∼2 M_⊙). Nevertheless, some NS ULX systems may also reach extremely high X-ray luminosities (>∼10^{41} erg/s)
- Publication:
-
The X-ray Universe 2017
- Pub Date:
- October 2017
- Bibcode:
- 2017xru..conf..237W