Abstract
We report on a Rossi X-Ray Timing Explorer observation of Aquila X-l during its outburst in 1997 March in which, immediately following a type I burst, the broadband 2-10 keV flux decreased by about 10% and the kilohertz quasi-periodic oscillation (kHz QPO) frequency decreased from 813 +/- 3 to 776 +/- 4 Hz. This change in kHz QPO frequency is much larger than expected from a simple extrapolation of a frequency-flux correlation that was established in data before the burst. Meanwhile, a very low frequency noise component in the broadband fast Fourier transform power spectra, with a fractional rms amplitude of 1.2% before the burst, ceased to exist after the burst. All these changes were accompanied by a change in the energy spectral shape. If we characterize the energy spectra with a model composed of two blackbody (BB) components and a power-law component, almost all the decrease in flux was in the two BE components. We attribute the two BE components to the contributions from a region very near the neutron star, or even from the neutron star itself, and from the accretion disk, respectively.
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