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Title: Evidence of a decrease of kHz quasi-periodic oscillation peak separation towards low frequencies in 4U 1728-34 (GX 354-0)
Author: Migliari, Simone
Van der Klis, M.
Fender, R. P.
Keywords: Estels de neutrons
Astronomia de raigs X
Neutron stars
X-ray astronomy
Issue Date: Nov-2003
Publisher: Royal Astronomical Society
Abstract: We have produced the colour-colour diagram of all the observations of 4U 1728-34 available in the Rossi X-ray Timing Explorer public archive (from 1996 to 2002) and found observations filling in a previously reported `gap' between the island and the banana X-ray states. We have made timing analysis of these gap observations and found, in one observation, two simultaneous kHz quasi-periodic oscillations (QPOs). The timing parameters of these kHz QPOs fit in the overall trend of the source. The `lower' kHz QPO has a centroid frequency of ~308 Hz. This is the lowest `lower' kHz QPO frequency ever observed in 4U 1728-34. The peak frequency separation between the `upper' and the `lower' kHz QPO is Δν= 274 +/- 11 Hz, significantly smaller than the constant value of Δν~ 350 Hz found when the `lower' kHz QPO frequency is between ~500 and 800 Hz. This is the first indication in this source for a significant decrease of kHz QPO peak separation towards low frequencies. We compare the result briefly to theoretical models for kHz QPO production.
Note: Reproducció del document publicat a:
It is part of: Monthly Notices of the Royal Astronomical Society, 2003, vol. 345, num. 3, p. L35-L39
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ISSN: 0035-8711
Appears in Collections:Articles publicats en revistes (Física Quàntica i Astrofísica)

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