2008/11/10 by A. R. King
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Pulsars and Gravitational Waves Research #astro-ph
paper · pdf · doi:10.1111/j.1745-3933.2008.00594.x
MNRAS Letters, in press
arxiv created 2008/11/10 · openalex publication_date 2008/12/31 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Abstract I suggest that the beaming factor in bright ultraluminous X-ray sources (ULXs) varies as , where is the Eddington ratio for accretion. This is required by the observed universal Lsoft∝T−4 relation between soft-excess luminosity and temperature, and is reasonable on general physical grounds. The beam scaling means that all observable properties of bright ULXs depend essentially only on the Eddington ratio , and that these systems vary mainly because the beaming is sensitive to the Eddington ratio. This suggests that bright ULXs are stellar-mass systems accreting at Eddington ratios of the order of 10–30, with beaming factors b≳ 0.1. Lower luminosity ULXs follow bolometric (not soft-excess) L∼T4 correlations and probably represent sub-Eddington accretion on to black holes with masses ∼10M⊙. High-mass X-ray binaries containing black holes or neutron stars and undergoing rapid thermal- or nuclear-time-scale mass transfer are excellent candidates for explaining both types. If the scaling for bright ULXs can be extrapolated to the Eddington ratios found in SS433, some objects currently identified as active galactic nuclei at modest redshifts might actually be ULXs (‘pseudo-blazars’). This may explain cases where the active source does not coincide with the centre of the host galaxy.