  Among the transient black hole binary systems, 4U 1630-47 is one of the most
active sources exhibiting outbursts every few hundred days, with every outburst
lasting typically around hundred days. During the 2002-2004 outburst the
appearance of quasi-periodic oscillations (QPOs) coincide with the onset of
anomalous state. There are two distinct QPO states: namely the single QPO state
with one QPO and the twin QPO state with two QPOs not related harmonically. The
spectral features of this state are corroborated by a previous outburst in
1998. The evolution of the inner disc temperature and the inner disc radius
suggest the possible onset of geometrically thicker, slim disc as a possible
explanation of the energy spectral features. The other possibilities involving
the Comptonizing cloud also exist that may explain the anomalous state. The two
different QPO states exhibit different spectral features, and we provide a
possible empirical physical scenario from the observation of the evolution of
the spectral features.
