1996/07/09 by M. van der Klis, M. Van der Klis, J. H. Swank +8 · 8 citations
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Geophysics and Sensor Technology #astro-ph
paper · pdf · doi:10.1086/310251
7 pages, 4 figures LaTeX, ApJ aas2pp4 style, to appear in ApJ Letters
arxiv created 1996/07/09 · openalex publication_date 1996/09/20 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/07/31
We report the discovery, with NASA's Rossi X-Ray Timing Explorer ( RXTE ), of the first submillisecond oscillations found in a celestial X-ray source. The quasi-periodic oscillations (QPOs) come from Sco X-1 and have a frequency of ~1100 Hz and amplitudes of 0.6%-1.2% (rms) and are relatively coherent, with Q up to ~10 2 . The frequency of the QPOs increases with accretion rate, rising from 1050 to 1130 Hz when the source moves from top to bottom along the normal branch in the X-ray color-color diagram, and shows a strong, approximately linear correlation with the frequency of the well-known 6-20 Hz normal/flaring-branch QPOs. We also report the discovery of QPOs with a frequency near 800 Hz that occur, simultaneously with the 1100 Hz QPOs, in the upper normal branch. We discuss several possible interpretations, one involving a millisecond X-ray pulsar whose pulses we see reflected off accretion flow inhomogeneities. Finally, we report the discovery of ~45 Hz QPOs, most prominent in the middle of the normal branch, which might be magnetospheric beat-frequency QPOs.