2001/01/23 by Martin Still, Kieran O'Brien, K. O’Brien +11 · 4 citations
Earth and Planetary Sciences · Physics and Astronomy · #Astro and Planetary Science #Astrophysical Phenomena and Observations #High-pressure geophysics and materials #astro-ph
paper · pdf · doi:10.1086/321337
18 pages, 7 figures. ApJ, in press
arxiv created 2001/01/23 · openalex publication_date 2001/06/10 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/04
We present RXTE observations of the eclipsing X-ray binary Hercules X-1 conducted during an anomalous low state. Data reduction reveals a light curve over 2.7 orbital cycles remarkably similar to optical and UV light curves which are dominated by the companion star. Count rates are modulated close to the orbital period, attaining a maximum when the inner face of the companion star, irradiated by X-rays from the compact source, is most-visible. Cold reflection provides an acceptable fit to the energy spectrum. Employing binary geometry to scale the model and assuming companion star reflection, we are able to reconstruct the incident X-rays which are removed from our direct line-of-sight (presumably by the accretion disk). We find the flux of the hidden source to be identical to the observed flux of Her X-1 at the peak of its main-high state. Consequently, Her X-1 is emitting a reflected spectrum, largely uncontaminated by direct X-rays in the anomalous low-state. The spectral energy distribution, period, amplitude and phasing of the modulation are all consistent with a companion star origin. Since this source occurs in a well-understood binary environment, it provides an excellent case study for more sensitive experiments in the future.