2002/09/30 by Keith W. Vanderlinde, Keith W. Vanderlinde, Alan M. Levine +3 · 9 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Intensity (physics) #Modulation (music) #Noise (video) #Orbit (dynamics) #Orbital mechanics #Orbital period #Period (music) #Radioactive Decay and Measurement Techniques #Relativity and Gravitational Theory #Sideband #Sky #astro-ph
paper · pdf · doi:10.1086/375388
published in Publications of the Astronomical Society of the Pacific 115(808), 739-747 (Institute of Physics) · AASTeX, 20 pages, 5 Postscript figures
arxiv created 2002/09/30 · openalex publication_date 2003/06/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The orbital period of Scorpius X‐1 has been accepted as 0.787313 days since its discovery in archival optical photometric data by Gottlieb, Wright, & Liller. This period has apparently been confirmed multiple times in the years since in both photometric and spectroscopic optical observations, although to date only marginal evidence has been reported for modulation of the X‐ray intensity at that period. We have used data taken with the All Sky Monitor on board the Rossi X‐Ray Timing Explorer over the past 6 years to search for such a modulation. A major difficulty in detecting the orbit in X‐ray data is presented by the flaring behavior in this source, wherein the (1.5–12 keV) X‐ray intensity can change by up to a factor of 2 within a fraction of a day. These flares contribute nearly white noise to Fourier transforms of the intensity time series and thereby tend to obscure weak modulations, i.e., of a few percent or less. We present herein a technique for substantially reducing the effects of the flaring behavior while, at the same time, retaining much of any periodic orbital modulation, provided only that the two temporal behaviors exhibit different spectral signatures. Through such a search, we have found evidence for orbital modulation at the ∼1% level with a period of 0.78893 days. This period is equal within our accuracy to a period (0.78901 days) that differs by 1 cycle yr −1 from the accepted value and that was also detected by Gottlieb et al. at a strength nearly as great as that of the 0.787313 day periodicity. We note that many of the reported optical observations of Sco X‐1 have been made within 1 or 2 months of early June, when Sco X‐1 transits the meridian at midnight. All periodicity searches based only on such observations would have been subject to the same 1 cycle yr −1 alias that affected the search of Gottlieb and coworkers. These considerations lead us to suggest that the actual period may in fact be 0.78901 days and that further observations will be necessary to confirm the true orbital period of Sco X‐1.