The Energy Dependence of the Aperiodic
نویسندگان
چکیده
Using the data from the Rossi X-ray Timing Explorer (RXTE), we report the diierent energy dependence of the variability of the four persistent hard X-ray sources in the low-hard state: Cygnus X{1, GX 339{4, GRS 1758-258 and 1E 1740.7{2942. Cygnus X{1 is found to have a atter 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 anti-correlates with the X-ray ux. 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.
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