Spectral variability modes of GX 339-4 in a hard-to-soft state   transition
  We report on INTEGRAL observations performed during the 2004 outburst of the bright black hole transient GX 339-4. We analysed IBIS and JEM-X public data starting on 9th August and lasting about one month. During this period GX 339-4 showed spectral state transitions. In order to seek for variability patterns, a principal component analysis (PCA) has been used. 
M. Del Santo, J. Malzac, P. Ubertini, T. Belloni