Bridging the gap between stellar-mass black holes and ultraluminous X-ray sources

Abstract

The X-ray spectral and timing properties of ultraluminous X-ray sources (ULXs) have many similarities with the very high state of stellar-mass black holes (power-law dominated, at accretion rates greater than the Eddington rate). On the other hand, their cool disk components, large characteristic inner-disk radii and low characteristic timescales have been interpreted as evidence of black hole masses ~ 1000 Msun (intermediate-mass black holes). Here we re-examine the physical interpretation of the cool disk model, in the context of accretion states of stellar-mass black holes. In particular, XTE J1550-564 can be considered the missing link between ULXs and stellar-mass black holes, because it exhibits a high-accretion-rate, low-disk-temperature state (ultraluminous branch). On the ultraluminous branch, the accretion rate is positively correlated with the disk truncation radius and the bolometric disk luminosity, while it is anti-correlated with the peak temperature and the frequency of quasi-periodic-oscillations. Two prototypical ULXs (NGC1313 X-1 and X-2) also seem to move along that branch. We use a phenomenological model to show how the different range of spectral and timing parameters found in the two classes of accreting black holes depends on both their masses and accretion rates. We suggest that ULXs are consistent with black hole masses ~ 50-100 Msun, moderately inefficiently accreting at ~20 times Eddington.

11 pages, accepted for publication in Astrophysics and Space Science. Based on work presented at the Fifth Stromlo Symposium, Australian National University, Dec 2006

References in corpus (8)

• X-ray Properties of Black-Hole Binaries
• Super-critically accreting stellar-mass black holes as ultraluminous X-ray sources
• XMM-Newton observations of the brightest Ultraluminous X-ray sources
• The Nature of SS433 and the Ultraluminous X-ray Sources
• Testing Accretion Disk Theory in Black Hole X-ray Binaries
• Spectral State Transitions of the Ultraluminous X-ray Sources X-1 and X-2 in NGC 1313
• On the weakness of disc models in bright ULXs
• Quasi Periodic Oscillations and Strongly Comptonized X-ray emission from Holmberg IX X-1

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• Evolution of the spectral curvature in the ULX Holmberg II X-1
• The slim-disk state of the ultraluminous X-ray source in M83
• Soft Extragalactic X-Ray Binaries at the Eddington Threshold
• Broadband X-ray spectral variability of the pulsing ULX NGC 1313 X-2
• No periodicity revealed for an "eclipsing" ultraluminous supersoft X-ray source in M81
• Investigation of X-ray timing and spectral properties of ESO 243-49 HLX-1 with long-term Swift Monitoring
• The peculiar spectral evolution of the new X-ray transient MAXI J0637-430
• Long-term Spectral Variability of the Ultra-luminous X-ray source Holmberg IX X--1
• Exploring the nature of ultra-luminous X-ray sources across stellar population ages using detailed binary evolution calculations
• Measuring the black hole mass in Ultraluminous X-ray Sources with the X-ray Scaling Method
• Gravitational Dynamics of Large Stellar Systems
• Broadband X-ray spectral analysis of the ULX NGC 1313\,X-1 using JeTCAF: Origin of the ULX bubble
• Binary populations and stellar dynamics in young clusters