Low and high frequency Quasi-Periodic Oscillations in 4U1915-05

The burster and dipper Low Mass X-ray Binary (LMXB) 4U1915-05 (also known as XB1916-053) was observed by the Rossi X-ray Timing Explorer (RXTE) 19 times for a total exposure of 140 ks between 1996 February and October. Here we report on the discovery of Low Frequency (10-40 Hz) Quasi-Periodic Oscillations (LFQPOs) from 4U1915-05. The properties of the LFQPOs are related to the presence of the High Frequency QPOs (HFQPOs) detected simultaneously. We have observed a correlation between the LFQPO frequency and source count rate, as well as a correlation (linear) between the LFQPOs and HFQPOs. Both results cannot be explained by a Beat Frequency Model (BFM). They are also hardly compatible with predictions from the inner disk precession model.