Low and high frequency quasi-periodic oscillations in 4U1915-05

The X-ray burster and dipper 4U1915-05 (also known as XB 1916-053) was obse rved 19 times for a total exposure of roughly 140 ks between 1996 February and October with the proportional counter array (PCA) aboard Rossi X-ray Ti ming Explorer (RXTE). We present here the detailed timing study of its X-ra y emission. The source was observed in both a high intensity/soft spectral and a low intensity/hard spectral state. The 2-20 keV luminosities are abou t 1.4 x 10(37) and 3.2 x 10(36) ergs s(-1) in the two regimes respectively (assuming a source distance of 9.3 kpc). We confirm that 4U1915-05 is an at oll source based on its spectral behaviour and its aperiodic variability in the frequency range similar to 4 x 10(-3) - 128 Hz. 4U1915-05 displays red noise below similar to 1 Hz, but is especially remarkable for its quasi-pe riodic variability detected for the first time at several timescales. We de tect low frequency quasi-periodic oscillations (LFQPOs) between similar to 5 and 80 Hz, as well as high frequency QPOs (HFQPOs) between similar to 200 and 1300 Hz. Both LFQPOs and HFQPOs frequencies positively correlate with the mass accretion rate inferred from the position of the source on the col or-color diagram. In a narrow range of luminosity, we also detect twin simu ltaneous HFQPOs separated by 348 +/- 12 Hz.