Timescale Invariance of Rapid X-Ray Variability of the Black Hole Candidate GRO J1719−24

We present the results of an analysis of the time variability of the soft X-ray transient GRO J1719-24 (Nova Oph 1993), as observed with BATSE. Our analysis covers the entire ~80 day outburst, beginning with the first detection of this black hole candidate on 1993 September 25. We obtained power density spectra (PDSs) of the data in the 20-100 keV energy band, covering the frequency interval 0.002-0.488 Hz. The PDSs show a significant quasi-periodic oscillation peak, the centroid frequency of which increased from ~0.04 Hz at the onset of the outburst to ~0.3 Hz at the end. Additional noise is present in the PDSs, which we describe in terms of two components. We find that the evolution of the PDSs can be described as a gradual stretching by a factor of ~7.5 in frequency of the power spectrum, accompanied by a decrease of the power level by the same factor, such that the integrated power in a scaled frequency interval remains constant.