RXTE Observations of 0.1–300 Hz Quasi‐periodic Oscillations in the Microquasar GRO J1655−40

Abstract

We have investigated 52 Rossi X-Ray Timing Explorer pointed observations of GRO J1655-40 spanning the X-ray outburst that commenced on 1996 April 25 and lasted for 16 months. Our X-ray timing analyses reveal four types of quasi-periodic oscillations (QPOs): three with relatively stable central frequencies near 300, 9, and 0.1 Hz, and a fourth QPO that varied over the range 14-28 Hz. The 300 and 0.1 Hz QPOs appear only when the power-law component dominates the X-ray spectrum and the estimated unabsorbed X-ray luminosity is above ~0.2L_Edd. At lower luminosity (L_X~0.1L_Edd), the thermal component dominates the spectrum; the disk appears somewhat cooler (~1.3 keV), and its inner radius appears larger.