New insights into ultraluminous X-ray sources from deep XMM-Newton observations

The controversy over whether ultraluminous X-ray sources (ULXs) contain a new intermediate-mass class of black holes (IMBHs) remains unresolved. We present new analyses of the deepest XMM-Newton observations of ULXs that address their underlying nature. We examine both empirical and physical modelli...

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Bibliographic Details
Published in:arXiv.org 2005-11
Main Authors: Roberts, T P, A -M Stobbart, Goad, M R, Warwick, R S, Wilms, J, Uttley, P, Reeves, J N
Format: Article
Language:English
Subjects:
Anomalies
Astronomical models
Curvature
Deposition
Empirical analysis
X ray sources
X ray spectra
X-ray astronomy
XMM (spacecraft)
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Summary:The controversy over whether ultraluminous X-ray sources (ULXs) contain a new intermediate-mass class of black holes (IMBHs) remains unresolved. We present new analyses of the deepest XMM-Newton observations of ULXs that address their underlying nature. We examine both empirical and physical modelling of the X-ray spectra of a sample of thirteen of the highest quality ULX datasets, and find that there are anomalies in modelling ULXs as accreting IMBHs with properties simply scaled-up from Galactic black holes. Most notably, spectral curvature above 2 keV in several sources implies the presence of an optically-thick, cool corona. We also present a new analysis of a 100 ks observation of Holmberg II X-1, in which a rigorous analysis of the temporal data limits the mass of its black hole to no more than 100 solar masses. We argue that a combination of these results points towards many (though not necessarily all) ULXs containing black holes that are at most a few 10s of solar mass in size.
ISSN:2331-8422
DOI:10.48550/arxiv.0511077