Low frequency QPO in GRO J1719--24
Session 116 -- Globular Clusters and Compact Objects
Oral presentation, Thursday, 12, 1995, 10:00am - 11:30am

## [116.06] Low frequency QPO in GRO J1719--24

F. van der Hooft (University of Amsterdam), C. Kouveliotou (USRA/MSFC), J. van Paradijs (University of Amsterdam, UAH), B. Rubin, M. Finger (USRA/MSFC), A. Harmon (NASA/MSFC), M. van der Klis (University of Amsterdam), W.H.G. Lewin (MIT), J.P. Norris (NASA/GSFC), G.J. Fishman (NASA/MSFC)

We present here the results of a time series analysis of the X-ray transient GRO J1719--24 (Nova Oph 1993) observed with the Burst And Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory (CGRO). Our analysis covers the entire 80 day outburst, between 25 September and 14 December, 1993. We have analyzed an average of 35 source-on time intervals per day, each 512 bins of 1.024 seconds long between 20 - 100 keV. In total, about $1.5 \cdot 10^{6}$ seconds of data were selected during the outburst of GRO J1719--24. The corresponding FFT Power Density Spectra (PDS) cover the frequency range between 0.002 - 0.5 Hz. During the rise of the source, the PDS show a significant broad peak, indicative of quasi-periodic oscillations (QPO) in the time series. The centroid frequency of the QPO increased from $\sim45$ mHz to $\sim80$ mHz during the first week of the outburst and then increased gradually, but more slowly, to about $\sim120$ mHz. The QPO are present in the PDS during the whole outburst of GRO J1719--24.