2008/03/25 by Yawei Hui, Y. Hui, Julian H. Krolik · 27 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Atmosphere (unit) #Black-body radiation #Brightness #Degeneracy (biology) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Optics #Photon #Physics #Radiation #Spectral line #Surface brightness #astro-ph
paper · pdf · doi:10.1086/587774
published in The Astrophysical Journal 679(2), 1405-1412 (IOP Publishing) · 22 pages, 3 figures, accepted by ApJ
arxiv created 2008/03/25 · openalex publication_date 2008/05/30 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have chosen six ultraluminous X-ray sources from the XMM-Newton archive whose spectra have high signal-to-noise ratio (S/N) and can be fitted solely with a disk model without requiring any power-law component. To estimate systematic errors in the inferred parameters, we fit every spectrum to two different disk models, one based on local blackbody emission (KERRBB) and one based on detailed atmosphere modeling (BHSPEC). Both incorporate full general relativistic treatment of the disk surface brightness profile, photon Doppler shifts, and photon trajectories. We found in every case that they give almost identical fits and similar acceptable parameters. The best-fit value of the most interesting parameter, the mass of the central object, is between 23 and 73 M ☉ in five of the six examples. In every case, the best-fit inclination angle and mass are correlated, in the sense that large mass corresponds to high inclination. Even after allowing for this degeneracy, we find that, with ≳99.9% formal statistical confidence, three of the six objects have mass ≳25 M ☉ ; for the other three, these data are consistent with a wide range of masses. A mass greater than several hundred M ☉ is unlikely for the three best-constrained objects. These fits also suggest comparatively rapid black hole spin in the three objects whose masses are relatively well determined, but our estimate of the spin is subject to significant systematic error having to do with uncertainty in the underlying surface brightness profile.