High frequency features in the 1998 outburst of 4U 1630-47

We report on the detection with RXTE of variable high frequency features in the power spectra of the black hole candidate 4U 1630-47 during its 1998 outburst. We find high frequency features during the rise and the early decay of the outburst in the range of similar to 100-300 Hz. The features are usually found to be broad, and have rms amplitudes of similar to 2-8%; their frequencies are correlated with count rate and anti-correlated with spectral hardness. Also, for the first time twin high frequency features are detected simultaneously, with a ratio in frequencies consistent with 1:4. Although some of the high frequency features are less coherent and stronger than found in other black hole sources, we show that they behave very similar to the high frequency features found in for instance XTE J1550-564.