[Previous] | [Session 23] | [Next]
H. C. Lee, R. Misra (Northwestern University)
An empirical Compton up-scattering model is described which reproduces both the fractional RMS vs. energy and the soft lags (of up to 60~\musec) in the 830~Hz QPO observed in 4U1608-52 on Mar.~6,~1996. These RXTE observations , which cover photon energies from 5~keV to 30~keV, contain the most constraining lag data publicly available.
The model assumes that a hot, uniform corona is cooled by input photons, characterized by a Wien spectrum, from cooler, underlying material. Oscillations in the temperature of the corona, which also heats the underlying material, lead to oscillations in the input photon temperature. A combination of the two variations gives rise to the observed QPO, with their relative contributions determined by enforcing energy conservation. All input parameters to the model, save a characteristic coronal size, are derived from the photon energy spectrum of the Mar.~6 observation. Fits to the fractional RMS and phase lag data for this kilohertz QPO imply that the corona involved is less than 20~km in extent.
HL is supported by NASA GSRP grant NGT~5-50172.