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Ultraluminous X-Ray Sources
Journal article   Peer reviewed

Ultraluminous X-Ray Sources

Philip Kaaret, Hua Feng and Timothy P Roberts
Annual review of astronomy and astrophysics, Vol.55(1), pp.303-341
08/18/2017
DOI: 10.1146/annurev-astro-091916-055259
url
https://arxiv.org/pdf/1703.10728View
Open Access

Abstract

We review observations of ultraluminous X-ray sources (ULXs). X-ray spectroscopic and timing studies of ULXs suggest a new accretion state distinct from those seen in Galactic stellar-mass black hole binaries. The detection of coherent pulsations indicates the presence of neutron-star accretors in three ULXs and therefore apparently super-Eddington luminosities. Optical and X-ray line profiles of ULXs and the properties of associated radio and optical nebulae suggest that ULXs produce powerful outflows, also indicative of super-Eddington accretion. We discuss models of super-Eddington accretion and their relationship to the observed behaviors of ULXs. We review the evidence for intermediate-mass black holes (IMBHs) in ULXs. We consider the implications of ULXs for super-Eddington accretion in active galactic nuclei, heating of the early Universe, and the origin of the black hole binary recently detected via gravitational waves.

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