Wenfei Yu25 min

Decomposition of Rapid Variability and New Understanding of Black Hole States

The conventional picture of black hole states is composed of a correspondence between energy spectral states and power spectral states. It has been known that in black hole binaries, thermal disk component shows little variability in the hard state. In the soft state, the power spectra turns into a power-law noise. Little was known about how the soft state power-law noise comes in. In the Swift observations of the black hole transient MAXI J1659-152, we discovered that in the hard and intermediate state, the power spectral shape is of a power-law type in the soft energy band below ~2 keV while the power spectrum in the hard band above ~2 keV is of typical hard or intermediate state. The power-law noise and the band-limited noise plus low-frequency QPO coexist in the soft and the hard bands, respectively. This is the first time the power spectral shape of the disk component in the hard/intermediate state is determined. We also found that the same phenomenon was seen in GRS 1915+105 in the XMM/Newton observations. These observations provide clear evidence that the power spectral state depends on which spectral component we are looking at. Thus there is no correspondence between the energy spectral state and the power spectral state in a broadband view. We discuss the implications of the broadband view on our understanding of rapid variability in black hole and neutron star XRBs.