2002/06/30 by J. M. Miller, J. M. Mïller, A. C. Fabian +7 · 1 citation
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Mechanics and Biomechanics Studies #astro-ph
paper · pdf · doi:10.1086/344047
published as Astrophys.J.577:L15-L18,2002 · 5 pages, 3 color figures. ApJ Letters, in press
arxiv created 2002/08/06 · openalex publication_date 2002/09/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
Broad Fe Kα emission lines have recently been reported in a number of Galactic black holes. Such lines are useful accretion flow diagnostics because they may be produced at the inner accretion disk and shaped by relativistic effects, but in general they have been observed only at luminosities of L X ~ 10 37 -10 38 ergs s -1 in soft X-rays. The Galactic microquasar V4641 Sgr—widely known for its 12.2 Crab (1.5-12 keV) outburst in 1999 September—displayed low-level activity in 1999 March. BeppoSAX observed the source in this state, and Fe Kα line emission was found by in 't Zand et al. In reanalyzing these data, we find strong evidence that the Fe Kα line profile is broadened. For the most likely values of the source distance and black hole mass measured by Orosz et al., our fits to the total spectrum indicate that the source was observed at a luminosity of L X = 1.9 × 10 36 ergs s -1 (2-10 keV), or L X / L Edd = 1.8 × 10 -3 . Advection-dominated accretion flow models predict a radially recessed disk in this regime. In contrast, fits to the observed Fe Kα emission-line profile with a relativistic line model constrain the inner disk to be consistent with the marginally stable circular orbit of a Schwarzschild black hole.