Crossing the Eddington limit: examining disk spectra at high accretion rates
arXiv:1611.09416 · doi:10.3847/1538-4357/836/1/48
Abstract
The faintest ultraluminous X-ray sources (ULXs), those with 0.3-10 keV luminosities 1 < L_X/10^39 < 3 erg s^-1, tend to have X-ray spectra that are disk-like but broader than expected for thin accretion disks. These `broadened disk' spectra are thought to indicate near- or mildly super-Eddington accretion onto stellar remnant black holes. Here we report that a sample of bright thermal-dominant black hole binaries, which have Eddington ratios constrained to moderate values, also show broadened disk spectra in the 0.3-10 keV band at an order of magnitude lower luminosities. This broadening would be missed in studies that only look above ~2 keV. While this may suggest that broadened disk ULXs could be powered by accretion onto massive stellar remnant black holes with close to maximal spin, we argue in favor of a scenario where they are at close to the Eddington luminosity, such that radiation pressure would be expected to result in geometrically slim, advective accretion disks. However, this implies that an additional physical mechanism is required to produce the observed broad spectra at low Eddington ratios.
20 pages, 7 figures, accepted for publication in ApJ
References in corpus (23)
- X-ray Properties of Black-Hole Binaries
- Modelling the behaviour of accretion flows in X-ray binaries
- An Ultraluminous X-ray Source Powered by An Accreting Neutron Star
- An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent
- The Effect of Pair-Instability Mass Loss on Black Hole Mergers
- Discovery of coherent pulsations from the Ultraluminous X-ray Source NGC 7793 P13
- XMM-Newton observations of the brightest Ultraluminous X-ray sources
- The magnetic nature of disk accretion onto black holes
- Clustering of Local Group distances: publication bias or correlated measurements? I. The Large Magellanic Cloud
- A Determination of the Spin of the Black Hole Primary in LMC X-1
- A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model
- Slim disks around Kerr black holes revisited
- X-ray irradiation in XTE J1817-330 and the inner radius of the truncated disc in the hard state
- Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817--330
- The Origin of Black Hole Spin in Galactic Low-Mass X-ray Binaries
- Initial Measurements of Black Hole Spin in GX 339-4 from Suzaku Spectroscopy
- Revealing accretion onto black holes: X-ray reflection throughout three outbursts of GX 339-4
- Angular Momentum Transport in Accretion Disks and its Implications for Spin Estimates in Black Hole Binaries
- Irradiated, colour-temperature-corrected accretion discs in ultraluminous X-ray sources
- The XMM-Newton view of the Crab
- Detailed Atmosphere Model Fits to Disk-Dominated ULX Spectra
- Millihertz quasi-periodic oscillations and broad iron line from LMC X-1
- X-Rays Beware: The Deepest Chandra Catalogue of Point Sources in M31