ULX behaviour: the ultraluminous state, winds & interesting anomalies

Abstract

Recent evidence - in particular the hard X-ray spectra obtained by NuSTAR, and the large amplitude hard X-ray variability observed when ultraluminous X-ray sources (ULXs) show soft spectra - reveals that common ULX behaviour is inconsistent with known sub-Eddington accretion modes, as would be expected for an intermediate-mass black hole (IMBH). Instead, it appears that the majority of ULXs are powered by super-Eddington accretion onto stellar-mass black holes. Here, we will review work that delves deeper into ULX spectral-timing behaviour, demonstrating it remains consistent with the expectations of super-Eddington accretion. One critical missing piece from this picture is the direct detection of the massive, radiatively-driven winds expected from ULXs as atomic emission/absorption line features in ULX spectra; we will show it is very likely these have already been detected as residuals in the soft X-ray spectra of ULXs. Finally, we will discuss ULXs that do not appear to conform to the emerging ULX behaviour patterns. In particular we discuss the implications of the identification of a good IMBH candidate as a background QSO; and the confirmation of an IMBH/ULX candidate in the galaxy NGC 2276 via the radio/X-ray fundamental plane.

6 pages, 7 figures. Proceedings of the 2015 XMM-Newton science workshop 'The extremes of black hole accretion', Madrid, 2015. Accepted for publication in Astronomische Nachrichten

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• X-ray observations of ultraluminous X-ray sources
• Supercritical Accretion Discs in Ultraluminous X-ray Sources and SS 433
• The powerful jet of an off-nuclear intermediate-mass black hole in the spiral galaxy NGC 2276
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• The hyperluminous X-ray source candidate in IC 4320: another HLX bites the dust
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Cited by in corpus (11)

• Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13
• Observational evidence for intermediate-mass black holes
• Intermediate Mass Black Hole Formation in compact Young Massive Star Clusters
• NGC 300 ULX1: A test case for accretion torque theory
• Radio activity of supermassive black holes with extremely high accretion rates
• The intrinsic collective X-ray spectrum of luminous high-mass X-ray binaries
• The ultraluminous X-ray source HoII X-1: kinematic evidence of its escape from the cluster
• Chandra X-ray Constraints on the Candidate Ca-rich Gap Transient SN 2016hnk
• Study on the magnetic field strength of NGC 300 ULX1
• NuSTAR and XMM-Newton observations of the ultraluminous X-ray source NGC 5643 X-1
• NuSTAR observations of the ultraluminous X-ray source M33 X-8: a black hole in a very high state?