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Ultra-luminous X-ray sources: X-ray binaries in a high/hard state?

Published online by Cambridge University Press:  01 August 2006

Z. Kuncic ,
R. Soria ,
C. K. Hung ,
M. C. Freeland  and
G. V. Bicknell
Z. Kuncic
Affiliation:
School of Physics, University of Sydney, Sydney NSW 2006, Australia email: [email protected]
R. Soria
Affiliation:
Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK email: [email protected]
C. K. Hung
Affiliation:
School of Physics, University of Sydney, Sydney NSW 2006, Australia email: [email protected]
M. C. Freeland
Affiliation:
School of Physics, University of Sydney, Sydney NSW 2006, Australia email: [email protected]
G. V. Bicknell
Affiliation:
Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Canberra ACT 2611, Australia email: [email protected]
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Abstract

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We examine the possibility that Ultraluminous X-ray sources (ULXs) represent the extreme end of the black hole X-ray binary (XRB) population. Based on their X-ray properties, we suggest that ULXs are persistently in a high/hard spectral state and we propose a new disk–jet model that can accomodate both a high accretion rate and a hard X-ray spectrum. Our model predicts that the modified disk emission can be substantially softer than that predicted by a standard disk as a result of jet cooling and this may explain the unusually soft components that are sometimes present in the spectra of bright ULXs. We also show that relativistic beaming of jet emission can indeed account for the high X-ray luminosities of ULXs, but strong beaming produces hard X-ray spectra that are inconsistent with observations. We predict the beamed synchrotron radio emission should have a flat spectrum with a flux density ≲0.01 mJy.

Keywords

accretion disks – black hole physics – X-rays: binaries
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S238: Black Holes from Stars to Galaxies – Across the Range of Masses , August 2006 , pp. 247 - 250
Copyright
Copyright © International Astronomical Union 2007

References

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