**title** Asp Conference Series, Vol. **volume**, **publication Year** **editors** Chandra and Rxte Observations of X-ray Novae
نویسنده
چکیده
We discuss new observations of X-ray novae with Chandra which provide strong evidence that black holes have event horizons. The evidence is based on the finding that black hole X-ray novae in quiescence are approximately 100 times fainter than equivalent neutron star X-ray novae. The advection-dominated accretion flow model provides a natural explanation for this difference. RXTE observations of XTE J1550-564 in the very high state, which were obtained during the 1998-1999 outburst of the source, reveal an extraordinarily tight correlation between the central frequency of the low frequency QPO and the soft, non-power-law flux in the 2-20 keV band. We discuss the nature of this soft spectral component and suggest the importance of obtaining direct observations of it at low energies (E < 2 keV) at the first available opportunity.
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