3 research outputs found
On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients
We studied the properties of the low-frequency quasi-periodic oscillations
detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322,
XTE J1859+226, 4U 1630-47,GX 339-4, XTE J1650-500) observed by the Rossi XTE
satellite. We analyzed the relation between the full width half maximum and the
frequency of all the narrow peaks detected in power density spectra where a
type-C QPO is observed. Our goal was to understand the nature of the modulation
of the signal by comparing the properties of different harmonic peaks in the
power density spectrum. We find that for the sources in our sample the width of
the fundamental and of the first harmonic are compatible with a frequency
modulation, while that of the sub-harmonic is independent of frequency,
possibly indicating the presence of an additional modulation in amplitude. We
compare our results with those obtained earlier from GRS 1915+105 and XTE
J1550-564.Comment: 8 pages, 3 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journa
Discovery of twin kHz quasi-periodic oscillations in the low-mass X-ray binary XTE J1701−407
We report the discovery of kHz quasi periodic oscillations (QPOs) in three
Rossi X-ray Timing Explorer observations of the low mass X-ray binary (LMXB)
XTE J1701-407. In one of the observations we detect a kHz QPO with a
characteristic frequency of 1153 +/- 5 Hz, while in the other two observations
we detect twin QPOs at characteristic frequencies of 740 +/- 5 Hz, 1112 +/- 17
Hz and 740 +/- 11 Hz, 1098 +/- 5 Hz. All detections happen when XTE J1701-407
was in its high intensity soft state, and their single trial significance are
in the 3.1-7.5 sigma range. The frequency difference in the centroid
frequencies of the twin kHz QPOs (385 +/- 13 Hz) is one of the largest seen
till date. The 3-30 keV fractional rms amplitude of the upper kHz QPO varies
between ~18 % and ~30 %. XTE J1701-407, with a persistent luminosity close to 1
% of the Eddington limit, is among the small group of low luminosity kHz QPO
sources and has the highest rms for the upper kHz QPO detected in any source.
The X-ray spectral and variability characteristics of this source indicate its
atoll source nature.Comment: 10 pages, 9 figures, accepted for publication in MNRA