A Comprehensive Energy-resolved Timing Analysis of XTE J1550–564

We present a study of low-frequency quasi-periodic oscillations (LFQPOs) in the Galactic black hole binary XTE J1550–564 during its 1998 outburst using data from RXTE. Light curves in eight energy bands from 0.1 to 13 keV were analyzed with Fourier techniques to produce energy-resolved power spectra. Each spectrum was modeled with three Lorentzians along with a power-law continuum. From these fits, we measured the peak frequency ( ν MAX ), quality factor ( Q ), and fractional rms amplitude ( r ) for each QPO. Our results show that r increases with energy, indicating that QPOs become more detectable at higher energies, while Q and ν MAX remain largely unchanged. This suggests that the trend in r is not due to changes in the QPO’s width or coherence, but rather to an increase in the continuum level with energy, which adds more power under the QPO features. These findings provide constraints for future modeling of LFQPO behavior.