Truncation of the inner accretion disk around a black hole at low luminosity
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Tomsick, John A. and Yamaoka, Kazutaka and Corbel, Stephane and Kaaret, Phillip and Kalemci, Emrah and Migliari, Simone (2009) Truncation of the inner accretion disk around a black hole at low luminosity. (Accepted/In Press)
Most black hole binaries show large changes in X-ray luminosity caused primarily
by variations in mass accretion rate. An important question for understanding
black hole accretion and jet production is whether the inner edge of
the accretion disk recedes at low accretion rate. Measurements of the location
of the inner edge (Rin) can be made using iron emission lines that arise due to
fluorescence of iron in the disk, and these indicate that Rin is very close to the black hole at high and moderate luminosities ( > 2% of the Eddington luminosity,LEdd). Here, we report on X-ray observations of the black hole GX 339–4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer (RXTE) that extend iron line studies to 0.24% LEdd and show that Rin increases by a factor of >27 over the value found when GX 339–4 was bright. The exact value of Rin depends on the inclination of the inner disk (i), and we derive 90% confidence limits of Rin > 35Rg at i = 0 degrees and Rin > 175Rg at i = 30 degrees. This provides direct evidence that the inner portion of the disk is not present at low luminosity, allowing for the possibility that the inner disk is replaced by advection- or magnetically-dominated accretion flows.
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