88 research outputs found
Disc atmospheres and winds in X-ray binaries
We review the current status of studies of disc atmospheres and winds in low
mass X-ray binaries. We discuss the possible wind launching mechanisms and
compare the predictions of the models with the existent observations. We
conclude that a combination of thermal and radiative pressure (the latter being
relevant at high luminosities) can explain the current observations of
atmospheres and winds in both neutron star and black hole binaries. Moreover,
these winds and atmospheres could contribute significantly to the broad iron
emission line observed in these systems.Comment: Accepted for publication in Acta Polytechnica. Invited review talk at
the Vulcano Workshop 2012: "Frontier Objects in Astrophysics and Particle
Physics
A highly-ionized absorber as a new explanation for the spectral changes during dips from X-ray binaries
Until now, the spectral changes observed from persistent to dipping intervals
in dipping low-mass X-ray binaries were explained by invoking progressive and
partial covering of an extended emission region. Here, we propose a novel and
simpler way to explain these spectral changes, which does not require any
partial covering and hence any extended corona, and further has the advantage
of explaining self-consistently the spectral changes both in the continuum and
the narrow absorption lines that are now revealed by XMM-Newton. In 4U 1323-62,
we detect Fe XXV and Fe XXVI absorption lines and model them for the first time
by including a complete photo-ionized absorber model rather than individual
Gaussian profiles. We demonstrate that the spectral changes both in the
continuum and the lines can be simply modeled by variations in the properties
of the ionized absorber. From persistent to dipping the photo-ionization
parameter decreases while the equivalent hydrogen column density of the ionized
absorber increases. In a recent work (see Diaz Trigo et al. in these
proceedings), we show that our new approach can be successfully applied to all
the other dipping sources that have been observed by XMM-Newton.Comment: 5 pages, 5 figures, to appear in the proceedings of "The X-ray
Universe 2005", San Lorenzo de El Escorial (Spain), 26-30 September 200
On the Low and High Frequency Correlation in Quasi-Periodic Oscillations Among White Dwarfs, Neutron Star and Black Hole Binaries
We interpret the correlation over five orders of magnitude between high
frequency and low frequency in a quasi-periodic oscillations (QPO) found by
Psaltis, Belloni & van der Klis (1999) for black hole (BH), neutron star (NS)
systems and then extended by Mauche (2002) to white dwarf (WD) binaries. We
argue that the observed correlation is a natural consequence of the Keplerian
disk flow adjustment to the innermost sub-Keplerian boundary conditions near
the central object. In the framework of the transition layer model the high
frequency is related to the Keplerian frequency at the outer (adjustment)
radius and the low frequency is related to the magnetoacoustic oscillation (MA)
frequency. Using a relation between the MA frequency the magnetic and gas
pressure and the density and the hydrostatic equilibrium condition in the disk
we infer a linear correlation the Keplerian frequency and the MA frequency. We
estimate the magnetic field strength near the TL outer radius for BHs NSs and
WDs. The fact that the observed high-low frequency correlation over five orders
of magnitude is valid for BHs, NSs, and down to WDs strongly rules out
relativistic models for QPO phenomena. We come to the conclusion that the QPOs
observations indicate the adjustment of the geometrically thin disk to
sub-Keplerian motion near the central object. This effect is a common feature
for a wide class of systems, starting from white dwarf binaries up to black
hole binaries.Comment: 8 pages, 1 figure, accepted for publication in the ApJ. Letters 2002
August
An XMM-Newton view of the dipping low-mass X-ray binary XTE J1710-281
(abridged) We analyzed the archived XMM-Newton observation of the poorly
studied low-mass X-ray binary XTE J1710-281 performed in 2004 that covered one
orbital period of the system (3.8 hr). The source shows dips as well as
eclipses, hence it is viewed close to edge-on. We modeled the spectral changes
between persistent and dips in the framework of the partial covering model and
the ionized absorber approach. The persistent spectrum can be fit by a power
law with a photon index of 1.94(+-0.02) affected by absorption from cool
material with a hydrogen column density of 0.401(+-0.007)*10^22 cm^-2. The
spectral changes from persistent to deep-dipping intervals are consistent with
the partial covering of the power-law emission, with the covering fraction
increasing from 26% during shallow dipping to 78% during deep dipping. We do
not detect any absorption lines from highly ionized species such as FeXXV. The
upper-limits we derive on their equivalent width (EW) are not constraining.
Despite not detecting any signatures of a warm absorber, we show that the
spectral changes are consistent with an increase in column density
(4.3(-0.5;+0.4)*10^22 cm^-2 during shallow dipping to 11.6(-0.6;+0.4)*10^22
cm^-2 during deep dipping) and a decrease in ionization state of a
highly-ionized absorber (10^2.52 during shallow dipping to 10^2.29 erg.s^-1.cm
during deep dipping), associated with a slight increase in the column density
of a neutral absorber. The parameters of the ionized absorber are not
constrained during persistent emission. The warm absorber model better accounts
for the ~1 keV depression visible in the pn dipping spectra, and naturally
explains it as a blend of lines and edges unresolved by pn. A deeper
observation of XTE J1710-281 would enable this interpretation to be confirmed.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Spectral changes during dipping in low-mass X-ray binaries due to highly-ionized absorbers
X-ray observations have revealed that many microquasars and low-mass X-ray
binaries (LMXBs) exhibit narrow absorption features identified with resonant
absorption from Fe XXV and Fe XXVI and other abundant ions. In many well
studied systems there is evidence for blue-shifts, indicating outflowing
plasmas. We succesfully model the changes in both the X-ray continuum and the
Fe absorption features during dips from all the bright dipping LMXBs observed
by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371
and XB 1916-053) as resulting primarily from an increase in column density and
a decrease in the ionization state of a highly-ionized absorber in a similar
way as was done for 4U 1323-62. This implies that the complex spectral changes
in the X-ray continua observed from the dip sources as a class can be most
simply explained primarily by changes in the highly ionized absorbers present
in these systems. There is no need to invoke unusual abundances or partial
covering of extended emission regions. Outside of the dips, the absorption line
properties do not vary strongly with orbital phase. This implies that the
ionized plasma has a cylindrical geometry with a maximum column density close
to the plane of the accretion disk. Since dipping sources are simply normal
LMXBs viewed from close to the orbital plane this implies that ionized plasmas
are a common feature of LMXBs.Comment: 19 pages, 11 figures, accepted for publication by Astronomy and
Astrophysic
Discovery of a 270 Hz X-Ray Burst Oscillation in the X-Ray Dipper 4U 1916-053
We report the discovery of a highly coherent oscillation in a type-I X-ray
burst observed from 4U 1916-053 by the Rossi X-ray Timing Explorer (RXTE). The
oscillation was most strongly detected approx. 1 s after the burst onset at a
frequency of 269.3 Hz, and it increased in frequency over the following 4
seconds of the burst decay to a maximum of around 272 Hz. The total measured
drift of 3.58 +/- 0.41 Hz (1 sigma) represents the largest fractional change in
frequency (1.32 +/- 0.15 %) yet observed in any burst oscillation. If the
asymptotic frequency of the oscillation is interpreted in terms of a decoupled
surface burning layer, the implied neutron star spin period is around 3.7 ms.
However, the expansion of the burning layer required to explain frequency drift
during the burst is around 80 m, substantially larger than expected
theoretically (assuming rigid rotation). The oscillation was not present in the
persistent emission before the burst, nor in the initial rise. When detected
its amplitude was 6-12% (RMS) with a roughly sinusoidal profile. The burst
containing the oscillation showed no evidence for photospheric radius
expansion, while at least 5 of the other 9 bursts observed from the source by
RXTE during 1996 and 1998 did. No comparable oscillations were detected in the
other bursts. A pair of kilohertz quasi-periodic oscillations (QPOs) has been
previously reported from this source with a mean separation of 348 +/- 12 Hz.
4U 1916-053 is the first example of a source where the burst oscillation
frequency is significantly smaller than the frequency separation of the kHz
QPOs.Comment: 8 pages, 2 figures, 2 tables; accepted for ApJ Letter
The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation
Gravitationally redshifted absorption lines from highly ionized iron have
been previously identified in the burst spectra of the neutron star in EXO
0748-676. To repeat this detection we obtained a long, nearly 600 ks
observation of the source with XMM-Newton in 2003. The spectral features seen
in the burst spectra from the initial data are not reproduced in the burst
spectra from this new data. In this paper we present the spectra from the 2003
observations and discuss the sensitivity of the absorption structure to changes
in the photospheric conditions.Comment: 18 Pages, 3 Figures. Accepted for publication in Ap
- …