Astron. Astrophys. 347, L23-L26 (1999)

1. Introduction

Over the last several years it has become widely accepted that the Galactic X-ray binaries exhibit Compton reflection features in their spectra.

Qualitatively, the reflection component in the X-ray spectra of these systems can be described as a broad "hump" at energies of 20-30 keV, a fluorescent Fe line at energies 6.4-6.7 keV (depending on the ionization state of the reflecting medium) and an absorption edge at the energy 7.1 keV ((Basko et al., 1974), (George & Fabian, 1991)). For all geometries which do not obscure the direct primary continuum from the observer, the detected energy spectra consists of this direct component (approximately a power law in the 3-13 keV energy band) and the reflection features. For standard cosmic abundances the expected equivalent width of the fluorescent Fe line is 100-200 eV (for a source above semi-infinite slab of neutral matter).

The geometry and mutual location of the source of primary continuum and reflecting medium should affect both the equivalent width of the fluorescent line and the character of it's variability. In particular the finite size of the reflector implies that the time variations of the reflected radiation should be smeared out on the time scales corresponding to the light crossing time of the reflector. In addition, time lags between different emission components might appear. Alternatively, the geometrically different region of the main energy release zone (where the primary continuum is produced) may have a different efficiency for the production of the reflection component. As a result the timing properties of the reprocessed component may be linked to the properties of the selected region of this zone.

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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