8,830 research outputs found
Spectral/timing evolution of black-hole binaries
I briefly outline the state-paradigm that has emerged from the study of
black-hole binaries with RossiXTE. This is the starting point of a number of
studies that address the connection between accretion and jet ejection and the
physical nature of the hard spectral components in these systems.Comment: 4 pages, 2 figures.To appear in Proceedings of "X-ray Astronomy 2009:
Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna,
Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin
On the harmonics of the low-frequency quasi-periodic oscillation in GRS 1915+105
GRS 1915+105 is a widely studied black hole binary, well known because of its
extremely fast and complex variability. Flaring periods of high variability
alternate with "stable" phases (the plateaux) when the flux is low, the spectra
are hard and the timing properties of the source are similar to those of a
number of black hole candidates in hard spectral state. In the plateaux the
power density spectra are dominated by a low frequency quasi periodic
oscillation (LFQPO) superposed onto a band limited noise continuum and
accompanied by at least one harmonic. In this paper we focus on three plateaux,
presenting the analysis of the power density spectra and in particular of the
LFQPO and its harmonics. While plotting the LFQPO and all the harmonics
together on a frequency-width plane, we found the presence of a positive trend
of broadening when the frequency increases. This trend can shed light in the
nature of the harmonic content of the LFQPO and challenges the usual
interpretation of these timing features.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
High-Frequency Quasi-Periodic Oscillations from GRS 1915+105
We report the results of a systematic timing analysis of all archival Rossi
X-Ray Timing Explorer (RXTE) observations of the bright black-hole binary GRS
1915+105 in order to detect high-frequency quasi-periodic oscillations (HFQPO).
We produced power-density spectra in two energy bands and limited the analysis
to the frequency range 30-1000 Hz. We found 51 peaks with a single trial
significance larger than 3 sigma. As all but three have centroid frequencies
that are distributed between 63 and 71 Hz, we consider most of them significant
regardless of the number of trials involved. The average centroid frequency and
FWHM are 67.3 +/- 2.0 Hz and 4.4 +/- 2.4 Hz respectively. Their fractional rms
varies between 0.4% and 2% (total band detections) and between 0.5% and 3%
(hard ban detections). As GRS 1915+105 shows large variability on time scales
longer than 1s, we analysed the data in 16s intervals and found that the
detections are limited to a specific region in the colour-colour diagram,
corresponding to state B of the source, when the energy spectrum is dominated
by a bright accretion disk component. However, the rms spectrum of the HFQPO is
very hard and does not show a flattening up to 40 keV, where the fractional rms
reaches 11%. We discuss our findings in terms of current proposed models and
compare them with the results on other black-hole binaries and neutron-star
binaries.Comment: 9 pages, 6 figures, Accepted for publication in MNRA
X-ray emission from the PSR B1259--63 system near apastron
The PSR B1259--63 system contains a 47 ms radio pulsar in a highly eccentric
binary with a Be-star companion. Strongly time variable X-ray emission was
reported from this system as the pulsar was near apastron in 1992-early 1993.
The variability was primarily deduced from an apparent non-detection of the
\psr system during a first pre-apastron \ros observation in February~1992. We
have re-analyzed the \ros observations of the \psr system. Contrary to the
results of a previous analysis, we find that the \psr system was detected by
\ros during the first off-axis February~1992 observation. The intensity of the
soft X-ray emission of the \psr system before and after the 1992 apastron
appears to vary at most by a factor . Our results sensibly constrain
theoretical models of X-ray emission from the \psr system.Comment: LATEX, Accepted for publ. in ApJ
On the kHz QPO frequency correlations in bright neutron star X-ray binaries
We re-examine the correlation between the frequencies of upper and lower kHz
quasi-periodic oscillations (QPO) in bright neutron-star low-mass X-ray
binaries. By including the kHz QPO frequencies of the X-ray binary Cir X-1 and
two accreting millisecond pulsars in our sample, we show that the full sample
does not support the class of theoretical models based on a single resonance,
while models based on relativistic precession or Alfven waves describe the data
better. Moreover, we show that the fact that all sources follow roughly the
same correlation over a finite frequency range creates a correlation between
the linear parameters of the fits to any sub-sample.Comment: Accepted for publication in MNRAS; 7 pages, 4 figure
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