RXTE/PCA observation of the X-ray burster 1E1724-3045 aperiodic variability of the persistent emission

Abstract

We report on the November 1996 Rossi X-ray Timing Explorer (RXTE) observation of the X-ray burster 1E1724-3045 with the Proportional Counter Array (PCA). The persistent X-ray emission shows a high level of noise variability, the so-called High Frequency Noise (HFN), with a fractional Root Mean Squared (RMS) of ∼ 25% in the 2 × 10 −3 − 40 Hz range (2–20 keV). The Fourier Power Density Spectrum (PDS) can be modeled in terms of the sum of two “shot noise” components with two characteristic timescales of 680 and 16 msec. The PDS contains also a third component: a broad Quasi Periodic Oscillation-like (QPO) feature centered at 0.8 Hz. Neither the shot timescales nor the QPO frequency do not vary with energy, whereas the integrated RMS of all three components shows a positive correlation. In addition, in the 2–20 keV energy band, we found significant evidence for a high frequency component which shows up to 500 Hz in the PDS. In terms of the shot noise model, a Lorentzian fit of this component implies a shot duration of about 1.4 ms. The reality of this component has been tested with the help of simulations. Our observation of the burster 1E1724-3045 reveals timing properties, such as low frequency QPO and high level of RMS for the HFN, also displayed by Black Hole Candidates (BHC).