The type B QPO phenomena in the transient black hole candidate GX 339-4

Abstract

We investigated the spectral and timing properties of the type B quasi-periodic oscillations (QPOs) showing up in the transient black hole binary GX 339-4 during its four outbursts observed by Rossi X-ray Timing Explorer (RXTE)/PCA and HEXTE in 2002, 2004, 2007 and 2010. We find that, the dependence on variability of the accretion flow turns out to be similar for the type B QPOs occurring in these four outbursts. We therefore take the results from the 2010 outburst for presentation. Our spectral results obtained from both the energy and time domains show that, the occurrence of the type B QPO is accompanied with sudden increase of hard component flux, relatively smaller inner disk radius, stable disk but variable corona. The latter may be understood in a scenario of variable input of seed photons for Comptonization in the corona. Further clues to probing the possible origination of the type B QPO come from our analysis of time lag and its energy dependence. The energy dependence of type B QPO amplitude suggests that the hard component dominate the variability and the time lag spectral analysis results suggests the type B QPO could be related to inverse Compton scattering. The time lag between hard and soft energy band is about 10 ms and found to depend on frequency ν in a form of ν−0.7 for type B QPOs in the rising phase. Finally we put these results in a context of a blob mechanism at work.