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An observational diagnostic for ultraluminous X-ray sources

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journal contribution
posted on 23.10.2019, 16:12 by V. Kalogera, M. Henninger, N. Ivanova, A. R. King
We consider observational tests for the nature of ultraluminous X-ray (ULX) sources. These tests must distinguish between thermal-timescale mass transfer onto stellar-mass black holes, leading to anisotropic X-ray emission, and accretion onto intermediate-mass black holes. We suggest that long-term transient behavior via the thermal-viscous disk instability could discriminate between these two possibilities for ULX sources in regions of young stellar populations. Thermal-timescale mass transfer generally produces stable disks and persistent X-ray emission. In contrast, mass transfer from massive stars to black holes produces unstable disks and thus transient behavior, provided that the black hole mass exceeds some minimum value MBH, min. This minimum mass depends primarily on the donor mass and evolutionary state. We show that MBH, min gsim 50 M☉ for a large fraction (gsim90%) of the mass transfer lifetime for the most likely donors in young clusters. Thus, if long-term monitoring reveals a large transient fraction among ULX sources in a young stellar population, these systems would be good candidates for intermediate-mass black holes in a statistical sense; information about the donor star is needed to make this identification secure in any individual case. A transient ULX population would imply a much larger population of quiescent systems of the same type.


We thank J. Miller, R. Taam, and A.Zezas for useful discussions. VK and ARK acknowledge the hospitality and support of the Aspen Center for Physics (Summer 2002). This work is partially supported by a David and Lucile Packard Science & Engineering Fellowship and a Chandra theory grant to VK, a NASA Summer Research fellowship fund to MH. ARK gratefully acknowledges a Royal Society Wolfson Research Merit Award, and the hospitality and support of the Theoretical Astrophysics Group at Northwestern University.



Astrophysical Journal, 2004, 603 (1), pp. L41-L44 (4)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Astrophysical Journal


American Astronomical Society, IOP Publishing





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