The Energy Dependence of the Aperiodic Variability for Cygnus X-1,
GX 339-4, GRS 1758-258, and 1E 1740.7-2942
Lin, D., Smith, I. A., Böttcher, M., and Liang, E. P.
Using the data from the Rossi X-Ray Timing Explorer (RXTE), we report the
different energy dependence of the variability of the four hard X-ray
sources in the hard/low state: Cygnus X-1, GX 339-4, GRS 1758-258, and 1E
1740.7-2942. Cygnus X-1 is found to have a flatter power density spectrum
(PDS) shape at higher energies. The other three sources have
energy-independent PDS shapes. The energy dependence of the overall
variability (the integrated rms amplitude) varies from source to source and
from observation to observation. 1E 1740.7-2942, for example, has a
variability generally increasing with energy while GX 339-4 has a decreasing
variability. A general trend is found in the four sources that the
integrated rms amplitude anticorrelates with the X-ray flux. We compare
these distinct energy-dependent behaviors with several emission models. None
of the models can fully explain all the features that we have found.
Status:
2000, ApJ, 531, 963 (March 10).
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