1,385 research outputs found
Identification of black hole power spectral components across all canonical states
From a uniform analysis of a large (8.5 Ms) Rossi X-ray Timing Explorer data
set of Low Mass X-ray Binaries, we present a complete identification of all the
variability components in the power spectra of black holes in their canonical
states. It is based on gradual frequency shifts of the components observed
between states, and uses a previous identification in the black hole low hard
state as a starting point. It is supported by correlations between the
frequencies in agreement with those previously found to hold for black hole and
neutron stars. Similar variability components are observed in neutron stars and
black holes (only the component observed at the highest frequencies is
different) which therefore cannot depend on source-specific characteristics
such as the magnetic field or surface of the neutron star or spin of the black
hole. As the same variability components are also observed across the jet-line
the X-ray variability cannot originate from the outer-jet but is most likely
produced in either the disk or the corona. We use the identification to
directly compare the difference in strength of the black hole and neutron star
variability and find these can be attributed to differences in frequency and
strength of high frequency features, and do not require the absence of any
components. Black holes attain their highest frequencies (in the
hard-intermediate and very-high states) at a level a factor ~6 below the
highest frequencies attained by the corresponding neutron star components,
which can be related to the mass difference between the compact objects in
these systems.Comment: 17 pages, 16 figures, accepted for publication in Ap
Do High Frequency QPOs Depend on Phase of Low Frequency QPOs in XTE J1550-564 ?
We have studied the dependence of the high frequency Quasi-periodic
Oscillation (QPO) (~284 Hz) on the phase of the low frequency QPO (~6 Hz) in
the black hole X-ray binary XTE J1550-564 in the observations of the Rossi
X-ray Timing Explorer (RXTE) performed on MJD 51241. By selecting the local
maxima and the local minima in the light curve on the 6 Hz QPO time scale, we
have found the corresponding high frequency QPO frequencies are consistent
within 1.5 sigma. However, the average central QPO frequency of the maxima and
the minima is about 2.0 sigma lower than the average high frequency QPO
frequency obtained in the entire observation. This marginally suggests that the
high frequency QPOs probably varies in frequency on short time scales. We
briefly discuss these results and their consequences.Comment: 3 pages, 1 figure, to appear in the Proceedings of the 4th
Microquasar Workshop, eds. Ph Durouchoux, Y. Fuchs and J. Rodriguez,
published by the Center for Space Physics: Kolkat
The aperiodic timing behaviour of the accretion-driven millisecond pulsar SAX J1808.4-3658
We studied the aperiodic X-ray timing behaviour of the accreting millisecond
pulsar SAX J1808.4-3658. The source was recently found to be the first
accreting millisecond pulsar that shows the kilohertz quasi-periodic
oscillations (kilohertz QPOs) that are found in many other X-ray binaries with
accreting neutron stars. The high frequency of these signals reflects the short
dynamical time scales in the region near the compact object where they
originate. We find that in addition to the kilohertz QPOs SAX J1808.4-3658
shows several low frequency timing features, based on which the source can be
classified as a so-called atoll source. The frequencies of the variability
components of the atoll sources follow a universal scheme of correlations. The
correlations in SAX J1808.4-3658 are similar but show a shift in upper
kilohertz QPO frequency. This discrepancy is perhaps related to a stronger or
differently configured magnetic field.Comment: 4 pages, 3 figures. To appear in the proceedings of the "The Restless
High-Energy Universe" (Amsterdam, The Netherlands), 2003, eds. E.P.J. van den
Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijer
The X-ray fast-time variability of Sco X-2 (GX 349+2) with RXTE
Sco X-2 (GX 349+2) is a low-mass X-ray binary and Z source. We have analysed
156 ks of Rossi X-ray Timing Explorer data, obtained in 1998 January, on this
source. We investigated the fast-time variability as a function of position on
the Z track. During these observations, Sco X-2 traced out the most extensive Z
track ever reported from this object, making this the most comprehensive study
thus far. We found the broad peaked flaring branch noise that is typical of Sco
X-2, with a centroid frequency in the range 3.3--5.8 Hz. We also discovered low
frequency noise, and a new peaked noise feature, with centroid frequencies in
the range 5.4--7.6 Hz and 11--54 Hz, respectively. We discuss the phenomenology
of these features, their relationship with the power spectral components found
in other low-mass X-ray binaries, and the implications for current models. In
particular, the low frequency noise we observed was strongest at intermediate
energies, in contrast to the low frequency noise seen in other Z sources. We
also detected very low frequency noise, and have calculated complex cross
spectra between intensity and hardness. We found that the very low frequency
noise is not entirely due to motion along the Z track.Comment: 17 pages, 9 figures, minor improvements, accepted for publication in
MNRA
The large-scale jet-powered radio nebula of Circinus X-1
We present multi-epoch observations of the radio nebula around the neutron
star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia
Telescope Compact Array between October 2000 and September 2004. The nebula can
be seen as a result of the interaction between the jet from the system and the
interstellar medium and it is likely that we are actually looking toward the
central X-ray binary system through the jet-powered radio lobe. The study of
the nebula thus offers a unique opportunity to estimate for the first time
using calorimetry the energetics of a jet from an object clearly identified as
a neutron star. An extensive discussion on the energetics of the complex is
presented: a first approach is based on the minimum energy estimation, while a
second one employs a self-similar model of the interaction between the jets and
the surrounding medium. The results suggest an age for the nebula of \leq 10^5
years and a corresponding time-averaged jet power \geq 10^{35} erg s^{-1}.
During periodic flaring episodes, the instantaneous jet power may reach values
of similar magnitude to the X-ray luminosity.Comment: Accepted to MNRA
Detection of anti-correlated hard X-ray time lag in Cygnus X-3
The wide-band X-ray spectra of the high mass X-ray binary Cygnus X-3 exhibits
a pivoting behavior in the `low' (as well as `hard') state, correlated to the
radio emission. The time scale of the soft and hard X-rays' anti-correlation,
which gave rise to the pivoting feature, was found to be less than a day from
the monitoring observations by RXTE--ASM and CGRO--BATSE. In this Letter we
report the detection of a lag of 1000s in the anti-correlation of
the hard X-ray emission (20--50 keV) to that of the soft X-ray emission (2--7
keV), which may be attributed to the viscous time scale of flow of matter in
the accretion disk. This suggests the geometrical picture of a truncated
accretion disc with a Compton cloud inside the disc, the relative sizes of
which determine the spectral shape. Any change in the disc structure will take
place in a viscous time scale, with corresponding anti-correlated change in the
Compton cloud. We also report the pivoting in the spectra in one span of a
pointed observation when an episode of the rearranging of the accretion system
is serendipitously observed. This is the first such observation of hard X-ray
delay seen in the persistent Galactic microquasars, within the precincts of the
hard state.Comment: Accepted in The Astrophysical Journal (Letters): in pres
Intrauterine repair of gastroschisis in fetal rabbits
Objective: Infants with gastroschisis (GS) still face severe morbidity. Prenatal closure may prevent gastrointestinal organ damage, but intrauterine GS repair (GSR) has not been established yet. Methods: In New Zealand White rabbits we developed and compared GS versus GSR: creation of GS was achieved by hysterotomy, right-sided laparotomy of the fetus and pressure on the abdominal wall to provoke evisceration. GSR was accomplished by careful reposition of eviscerated organs and a running suture of the fetal abdominal wall. For study purposes, 18 animals were divided equally into 3 groups: GS, GS with GSR after 2 h, and unmanipulated controls (C). Vitality was assessed by echocardiography. After 5 h all animals were sacrificed. Results: GSR inflicted no increased mortality, because all fetuses survived GS or GS with GSR. All fetuses with GS demonstrated significant evisceration of abdominal organs. In contrast, the abdominal wall of the fetuses from GSR was intact. Conclusion:The present animal model demonstrated the technical feasibility and success of an intrauterine repair of GS for the first time. However, further long-term studies (leaving GS and GSR in utero for several days) will be necessary to compare survival rates and intestinal injury, motility or absorption. The clinical application of GSR in utero remains a vision so far. Copyright (C) 2003 S. Karger AG, Basel
Quasi-periodic X-ray brightness fluctuations in an accreting millisecond pulsar
The relativistic plasma flows onto neutron stars that are accreting material
from stellar companions can be used to probe strong-field gravity as well as
the physical conditions in the supranuclear-density interiors of neutron stars.
Plasma inhomogeneities orbiting a few kilometres above the stars are observable
as X-ray brightness fluctuations on the millisecond dynamical timescale of the
flows. Two frequencies in the kilohertz range dominate these fluctuations: the
twin kilohertz quasi-periodic oscillations (kHz QPOs). Competing models for the
origins of these oscillations (based on orbital motions) all predict that they
should be related to the stellar spin frequency, but tests have been difficult
because the spins were not unambiguously known. Here we report the detection of
kHz QPOs from a pulsar whose spin frequency is known. Our measurements
establish a clear link between kHz QPOs and stellar spin, but one not predicted
by any current model. A new approach to understanding kHz QPOs is now required.
We suggest that a resonance between the spin and general relativistic orbital
and epicyclic frequencies could provide the observed relation between QPOs and
spin.Comment: Published in the 2003 July 3 issue of Natur
Low-frequency QPO from the 11 Hz accreting pulsar in Terzan 5: not frame dragging
We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz
accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5.
During these observations we find power spectra which resemble those seen in
Z-type high-luminosity neutron star low-mass X-ray binaries, with a
quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz
QPO and broad band noise. Using well known frequency-frequency correlations, we
identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which
were previously suggested to be due to Lense-Thirring precession. As IGR
J17480-2446 spins more than an order of magnitude more slowly than any of the
other neutron stars where these QPOs were found, this QPO can not be explained
by frame dragging. By extension, this casts doubt on the Lense-Thirring
precession model for other low-frequency QPOs in neutron-star and perhaps even
black-hole systems.Comment: 6 pages, 5 figures, Accepted for publication in ApJ
A second black hole candidate in a M31 globular cluster is identified with XMM-Newton
We use arguments developed in previous work to identify a second black hole
candidate associated with a M31 globular cluster, Bo 144, on the basis of X-ray
spectral and timing properties. The 2002 XMM-Newton observation of the
associated X-ray source (hereafter XBo 144) revealed behaviour that is common
to all low-mass X-ray binaries (LMXBs) in the low-hard state. Studies have
shown that neutron star LMXBs exhibit this behaviour at 0.01-1000 keV
luminosities <=10% of the Eddington limit (L_Edd). However, the unabsorbed
0.3-10 keV XBo 144 luminosity was ~0.30 L_Edd for a 1.4 M_sun neutron star, and
the expected 0.01-1000 keV luminosity is 3-7 times higher. We therefore
identify XBo 144 as a black hole candidate. Furthermore, it is the second black
hole candidate to be consistent with formation via tidal capture of a mean
sequence donor in a GC; such systems were previously though non-existent,
because the donor was thought to be disrupted during the capture process.Comment: Accepted for publication in MRAS letters. Four pages, three figure
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