634 research outputs found
Strong Correlation Between Noise Features at Low Frequency and the Kilohertz QPOs in the X-Ray Binary 4U 1728-34
We study the timing properties of the low mass X-ray binary 4U 1728-34 using
recently released data from the Rossi X-Ray Timing Explorer. This binary, like
many others with accreting neutron stars, is known to exhibit strong
quasi-periodic oscillations (QPOs) of its X-ray flux near 1 kHz. In addition to
the kilohertz QPOs, the Fourier power spectra show a broken power law noise
component, with a break frequency between 1 and 50 Hz, and a Lorentzian between
10 and 50 Hz. We find that the frequencies of the break and the low-frequency
Lorentzian are well correlated with the frequencies of the kilohertz QPOs. The
slope of the correlation is similar to that expected if the oscillations are
due to relativistic frame dragging (Lense-Thirring precession) in the inner
accretion disk (Stella & Vietri 1998). The correlation is also nearly identical
to the one found in Z-sources between the the well known QPOs on the horizontal
branch and the kilohertz QPOs, suggesting that the low frequency oscillations
are a similar phenomenon in these sources. The frequency of the break in the
power spectra is also correlated with the frequencies of the kilohertz QPOs. As
previously noted for the similar binaries 4U 1608-50 and 4U 1705-44, this
broken power law component closely resembles that of black hole candidates in
the low state, where the break frequency is taken as an indicator of mass
accretion rate. The relation between break frequency and kilohertz QPO
frequency thus provides additional proof that the frequency of the kilohertz
QPOs increases with mass accretion rate.Comment: ApJL in press, see the 'QPO page' at
http://www.astro.uva.nl/ecford/qpos.htm
Correlations in Quasi-Periodic Oscillation and Noise Frequencies Among Neutron-Star and Black-Hole X-ray Binaries
We study systematically the ~0.1-1200 Hz quasi-periodic oscillations (QPOs)
and broad noise components observed in the power spectra of non-pulsing
neutron-star and black-hole low-mass X-ray binaries. We show that among these
components we can identify two, occurring over a wide range of source types and
luminosities, whose frequencies follow a tight correlation. The variability
components involved in this correlation include neutron-star kilohertz QPOs and
horizontal-branch oscillations, as well as black-hole QPOs and noise
components. Our results suggest that the same types of variability may occur in
both neutron-star and black-hole systems over three orders of magnitude in
frequency and with coherences that vary widely but systematically. Confirmation
of this hypothesis will strongly constrain theoretical models of these
phenomena and provide additional clues to understanding their nature.Comment: 15 pages, 2 figures (one color figure), to appear in the
Astrophysical Journa
Timing properties and spectral states in Aquila X-1
We have analyzed five X-ray outbursts of the neutron-star soft X-ray
transient Aql X-1 and investigated the timing properties of the source in
correlation with its spectral states as defined by different positions in the
color-color and hardness-intensity diagrams. The hard color and the source
count rate serve as the distinguishing parameters giving rise to three spectral
states: a low-intensity hard state, an intermediate state and a high-intensity
soft state. These states are respectively identified with the extreme island,
island and banana states that characterize the atoll sources. The large amount
of data analyzed allowed us to perform for the first time a detailed timing
analysis of the extreme island state. Differences in the aperiodic variability
between the rise and the decay of the X-ray outbursts are found in this state:
at the same place in the color-color diagram, during the rise the source
exhibits more power at low frequencies (< 1 Hz), whereas during the decay the
source is more variable at high frequencies (> 100 Hz). The very-low frequency
noise that characterizes the banana-state power spectra below 1 Hz cannot be
described in terms of a single power law but a two-component model is required.
In two outbursts a new 6-10 Hz QPO has been discovered and tentatively
identified with the normal/flaring branch-like oscillation observed only at the
highest inferred mass accretion rates. We have compared the spectral and timing
properties of Aql X-1 with those of other atoll and Z sources. Our results
argue against a unification scheme for these two types of neutron-star X-ray
binaries.Comment: 24 pages, 4 tables, 9 figures, accepted for publication in Ap
X-Ray and UV Orbital Phase Dependence in LMC X-3
The black-hole binary LMC X-3 is known to be variable on time scales of days
to years. We investigate X-ray and ultraviolet variability in the system as a
function of the 1.7 day binary phase using a 6.4 day observation with the Rossi
X-ray Timing Explorer (RXTE) from December 1998. An abrupt 14% flux decrease,
lasting nearly an entire orbit, is followed by a return to previous flux
levels. This behavior occurs twice, at nearly the same binary phase, but it is
not present in consecutive orbits. When the X-ray flux is at lower intensity, a
periodic amplitude modulation of 7% is evident in data folded modulo the
orbital period. The higher intensity data show weaker correlation with phase.
This is the first report of X-ray variability at the orbital period of LMC X-3.
Archival RXTE observations of LMC X--3 during a high flux state in December
1996 show similar phase dependence. An ultraviolet light curve obtained with
the High Speed Photometer aboard the Hubble Space Telescope shows orbital
modulation consistent with that in the optical, caused by the ellipsoidal
variation of the spatially deformed companion.
The X-ray spectrum of LMC X-3 can be acceptably represented by a
phenomenological disk-black-body plus a power law. Changes in the spectrum of
LMC X-3 during our observations are compatible with earlier observations during
which variations in the 2-10 keV flux are tracked closely by the disk geometry
spectral model parameter.Comment: 11 pages, 7 figures, ApJ in pres
Reduced magnetic braking and the magnetic capture model for the formation of ultra-compact binaries
A binary in which a slightly evolved star starts mass transfer to a neutron
star can evolve towards ultra-short orbital periods under the influence of
magnetic braking. This is called magnetic capture. In a previous paper we
showed that ultra-short periods are only reached for an extremely small range
of initial binary parameters, in particular orbital period and donor mass. Our
conclusion was based on one specific choice for the law of magnetic braking,
and for the loss of mass and angular momentum during mass transfer. In this
paper we show that for less efficient magnetic braking it is impossible to
evolve to ultra-short periods, independent of the amount of mass and associated
angular momentum lost from the binary.Comment: 7 pages, 7 figures, accepted for publication in Astronomy and
Astrophysics. See http://www.astro.uu.nl/~sluys/PhD
Is Cygnus X-3 a low-mass X-ray binary?
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
``Canonical'' Black Hole States in the Superluminal Source GRO J1655-40
We analyze RXTE/PCA observations of the black hole candidate and galactic
superluminal source GRO J1655-40 during its recent outburst. We show that
during its decay to quiescence, GRO J1655-40 goes through the high,
intermediate, and low state (and that at the beginning of its decay it might
have even shown signatures of a very high state), just like other black hole
candidates. This is the first time that such a transition is observed in a
galactic superluminal source. We discuss what are the implications of these
results on the hypothesis that the spin of the black hole in superluminal
sources is much higher than in other black hole candidates.Comment: To appear in ApJL. AAS LaTex v4.0 (9 pages, 2 ps-figures
Testing the transition layer model of quasi-periodic oscillations in neutron star X-ray binarie
We compare the theoretical predictions of the transition layer model with
some observational features of quasi-periodic oscillations (QPOs) in neutron
star X-ray binaries. We found that the correlation between horizontal branch
oscillation (HBO) frequencies and kilohertz (kHz) QPO frequencies, the
difference between the low-frequency QPOs in atoll sources and HBOs in Z
sources, and the correlation between the frequencies of low-frequency QPOs and
break frequencies can be well explained by the transition layer model, provided
the neutron star mass is around 1.4 solar mass and the angle between
magnetosphere equator and accretion disk plane is around 6 degree. The observed
decrease of peak separation between two kHz QPO frequencies with the increase
of kHz QPO frequencies and the increase of QPO frequencies with the increase of
inferred mass accretion rate are also consistent with the theoretical
predictions of transition layer model. In addition, we derive a simple equation
that can be adopted to estimate the angle () between magnetosphere
equator and accretion disk plane by use of the simultaneously observed QPO
frequency data. We estimate these angles, in the range of 4 to 8 degrees, for
five Z sources and two atoll sources. The nearly constant value for
each source, derived from the different sets of simultaneously observed QPO
frequency data, provides a strong test of the theoretical model. Finally, we
suggest that the similar transition layer oscillations may be also responsible
for the observed QPOs in accretion-powered millisecond X-ray pulsar and
Galactic black hole candidates.Comment: 10 pages, 5 figures, to appear in ApJ, Vol. 55
Interpreting the High Frequency QPO Power Spectra of Accreting Black Holes
In the context of a relativistic hot spot model, we investigate different
physical mechanisms to explain the behavior of quasi-periodic oscillations
(QPOs) from accreting black holes. The locations and amplitudes of the QPO
peaks are determined by the ray-tracing calculations presented in Schnittman &
Bertschinger (2004a): the black hole mass and angular momentum give the
geodesic coordinate frequencies, while the disk inclination and the hot spot
size, shape, and overbrightness give the amplitudes of the different peaks. In
this paper additional features are added to the existing model to explain the
broadening of the QPO peaks as well as the damping of higher frequency
harmonics in the power spectrum. We present a number of analytic results that
closely agree with more detailed numerical calculations. Four primary pieces
are developed: the addition of multiple hot spots with random phases, a finite
width in the distribution of geodesic orbits, Poisson sampling of the detected
photons, and the scattering of photons from the hot spot through a corona of
hot electrons around the black hole. Finally, the complete model is used to fit
the observed power spectra of both type A and type B QPOs seen in XTE
J1550-564, giving confidence limits on each of the model parameters.Comment: 30 pages, 5 figures, submitted to Ap
- âŠ