The bimodal spectral and QPO-behaviour of GX 17+2.
Abstract
The spectral and temporal analysis of Exosat observations of the bright galactic bulge source GX 17+2 is presented. The source shows a bimodal spectral and temporal behavior. High-frequency (24-28 Hz) quasi-periodic oscillations (QPO) are found on the horizontal branch of the H-I-diagram. There is evidence for a second harmonic at 50 Hz. QPOs with a nearly constant centroid frequency around 7 Hz are connected with the normal branch spectral behavior. Additionally, the continuum noise components exhibit a correlation with the twofold spectral behavior. Low frequency noise (LFN) is observed exclusively on the horizontal branch. On the normal branch, only very low frequency noise fluctuations on the timescale of several minutes are observed. The photon energy spectrum of GX 17+2 can be described by two components, a blackbody and a Boltzmann-Wien type spectrum. The spectrum of the horizontal branch is much harder than the normal branch spectrum. On the normal branch, up to 50 percent of the photons come from the blackbody component.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1990
- Bibcode:
- 1990A&A...228...89L
- Keywords:
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- Neutron Stars;
- Stellar Oscillations;
- Stellar Spectra;
- X Ray Binaries;
- Emission Spectra;
- Exosat Satellite;
- Galactic Bulge;
- Power Spectra;
- Astrophysics