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Title: ULXs: Neutron stars versus black holes
Authors: King, Andrew
Lasota, J-P.
First Published: 6-Feb-2016
Publisher: Oxford University Press (OUP), Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, (May 01, 2016) 458 (1): L10-L13.
Abstract: We consider ultraluminous X–ray systems (ULXs) where the accretor is a neutron star rather than a black hole. We show that the recently discovered example (M82 X–2) fits naturally into the simple picture of ULXs as beamed X–ray sources fed at super-Eddington rates, provided that its magnetic field is weaker (≃1011G) than a new-born X-ray pulsar, as expected if there has been mass gain. Continuing accretion is likely to weaken the field to the point that pulsing stops, and make the system indistinguishable from a ULX containing a black hole. Accordingly we suggest that a significant fraction of all ULXs may actually contain neutron star accretors rather than black holes, reflecting the neutron-star fraction among their X-ray binary progenitors. We emphasize that neutron-star ULXs are likely to have higher apparent luminosities than black hole ULXs for a given mass transfer rate, as their tighter beaming outweighs their lower Eddington luminosities. This further increases the likely proportion of neutron-star accretors among all ULXs. Cygnus X–2 is probably a typical descendant of neutron-star ULXs, which may therefore ultimately end as millisecond pulsar binaries with massive white dwarf companions.
DOI Link: 10.1093/mnrasl/slw011
ISSN: 0035-8711
eISSN: 1365-2966
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Creative Commons “Attribution Non-Commercial No Derivatives” licence CC BY-NC-ND, further details of which can be found via the following link: Archived with reference to SHERPA/RoMEO and publisher website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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