Models of ultraluminous X-ray sources with intermediate-mass black holes

Journal article

We have computed models for ultraluminous X-ray sources ( ULXs) consisting of a black hole accretor of intermediate mass (IMBH; e.g., ~1000 M⊙) and a captured donor star. For each of four different sets of initial donor masses and orbital separations we computed 30,000 binaryevolution models using a full Henyey stellar evolution code. To our knowledge, this is the first time that a population of X-ray binaries this large has been carried out with other than approximation methods, and it serves to demonstrate the feasibility of this approach to large-scale population studies of mass transfer binaries. In the present study, we find that in order to have a plausible efficiency for producing active ULX systems with IMBHs having luminosities ≳10^40 ergs s^-1, there are two basic requirements for the capture of companion/donor stars. First, the donor stars should be massive, i.e., ≳8M⊙. Second, the initial orbital separations after circularization should be close, i.e., ≲6–30 times the radius of the donor star when on the main sequence. Even under these optimistic conditions, we show that the production rate of IMBH-ULX systems may fall short of the observed values by factors of 10–100.

Authors: Madhusudhan, N; Justham, S; Nelson, L; Paxton, B; Pfahl, E

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: Astrophysical Journal
• Volume: 640
• Issue: 2
• Pages: 918-922
• Publication date: 2006-04-01
• Acceptance date: 2005-11-30
• DOI: 10.1086/500238
• Keywords: astro-ph
• Subjects: black hole physics; galaxies: star clusters; accretion, accretion disks; X-rays: binaries