Evidence of Energy-dependence of Power Spectral States of Black Hole Binaries and the Origin of the X-ray Variability
Abstract
In the conventional picture of black hole X-ray spectral states, there is a correspondence between the individual X-ray spectral state and the power spectral state. However, in the Swift and the RXTE observations of the 2010 outburst, the black hole transient MAXI J1659-152 showed power spectra of a power-law noise (PLN) below 2 keV and a band-limited noise (BLN) plus quasi-periodic oscillations above 2 keV, respectively. The emergence of the PLN and the fading of the BLN and QPOs took place from below 2 keV when the source entered the hard intermediate state and finally settled in the soft state three weeks later. This was accompanied by the emergence of the disk spectral component and the decreases of the variability amplitudes in the UV, the soft X-ray and the hard X-ray bands. Our results support that the PLN is associated with the optically thick disk in both hard and intermedi- ate states, and the X-ray power spectral state is independent of the energy spectral state in a broadband view, challenging the conventional description of black hole X-ray states. We suggest that the energy cut-offs of the PLN and the BLN or QPOs follow the temperature of the seed photons from the inner edge of the optically thick disk which generates the observed energy-dependence.
- Publication:
-
AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1312626Y