674 research outputs found
A variable magnetic disc wind in the black hole X-ray binary GRS 1915+105?
Context. GRS 1915+105 being one of the brightest transient black hole binaries (BHBs) in the X-rays offers a unique testbed for the study of the connection between accretion and ejection mechanisms in BHBs. In particular, this source can be used to study the accretion disc wind and its dependence on the state changes in BHBs.Aims. Our aim is to investigate the origin and geometry of the accretion disc wind in GRS 1915+105. This study will provide a basis for planning future observations with the X-ray Imaging Spectroscopy Mission (XRISM), and may also provide important parameters for estimating the polarimetric signal with the upcoming Imaging X-ray Polarimetry Explorer (IXPE).Methods. We analysed the spectra of GRS 1915+105 in the soft and hard chi classes using the high-resolution spectroscopy offered by Chandra HETGS. In the soft state, we find a series of wind absorption lines that follow a non-linear dependence of velocity width, velocity shift, and equivalent width with respect to ionisation, indicating a multiple component or stratified outflow. In the hard state we find only a faint Fe XXVI absorption line. We model the absorption lines in both the states using a dedicated magneto-hydrodynamic (MHD) wind model to investigate a magnetic origin of the wind and to probe the cause of variability in the observed line flux between the two states.Conclusions. The MHD disc wind model provides a good fit for both states, indicating the possibility of a magnetic origin of the wind. The multiple ionisation components of the wind are well characterised as a stratification of the same magnetic outflow. We find that the observed variability in the line flux between soft and hard states cannot be explained by photo-ionisation alone but is most likely due to a large (three orders of magnitude) increase in the wind density. We find the mass outflow rate of the wind to be comparable to the accretion rate, suggesting an intimate link between accretion and ejection processes that lead to state changes in BHBs
Modeling magnetic disk wind state transitions in black hole X-Ray binaries
We analyze three prototypical black hole X-ray binaries, 4U 1630-472, GRO J1655-40, and H1743-322, in an effort to systematically understand the intrinsic state transition of the observed accretion disk winds between wind-on and wind-off states by utilizing state-of-the-art Chandra/HETGS archival data from multi-epoch observations. We apply our magnetically driven wind models in the context of magnetohydrodynamic (MHD) calculations to constrain (1) their global density slope (p), (2) their density (n (17)) at the foot point of the innermost launching radius, and (3) the abundances of heavier elements (A (Fe,S,Si)). Incorporating the MHD winds into xstar photoionization calculations in a self-consistent manner, we create a library of synthetic absorption spectra given the observed X-ray continua. Our analysis clearly indicates a characteristic bimodal transition of multi-ion X-ray winds; i.e., the wind density gradient is found to steepen (from p similar to 1.2-1.4 to similar to 1.4-1.5) while its density normalization declines as the source transitions from the wind-on to the wind-off state. The model implies that the ionized wind remains physically present even in the wind-off state, despite its apparent absence in the observed spectra. Supersolar abundances for heavier elements are also favored. Our global multi-ion wind models, taking into account soft X-ray ions as well as Fe K absorbers, show that the internal wind condition plays an important role in wind transitions besides photoionization changes. Simulated XRISM/Resolve and Athena/X-IFU spectra are presented to demonstrate a high fidelity of the multi-ion wind model for a better understanding of these powerful ionized winds in the coming decades
Giant Planar Hall Effect in Epitaxial (Ga,Mn)As Devices
Large Hall resistance jumps are observed in microdevices patterned from
epitaxial (Ga,Mn)As layers when subjected to a swept, in-plane magnetic field.
This giant planar Hall effect is four orders of magnitude greater than
previously observed in metallic ferromagnets. This enables extremely sensitive
measurements of the angle-dependent magnetic properties of (Ga,Mn)As. The
magnetic anisotropy fields deduced from these measurements are compared with
theoretical predictions.Comment: 3 figure
On the importance of special relativistic effects in modelling ultra-fast outflows
Outflows are observed in a variety of astrophysical sources. Remarkably,
ultra-fast (), outflows in the UV and X-ray bands are often seen in
AGNs. Depending on their energy and mass outflow rate, respectively
, such outflows may play a key role in regulating
the AGN-host galaxy co-evolution process through cosmic time. It is therefore
crucial to provide accurate estimates of the wind properties. Here, we
concentrate on special relativistic effects concerning the interaction of light
with matter moving at relativistic speed relatively to the source of radiation.
Our aim is to assess the impact of these effects on the observed properties of
the outflows and implement a relativistic correction in the existing spectral
modelling routines. We define a simple procedure to incorporate relativistic
effects in radiative transfer codes. Following this procedure, we run a series
of simulations to explore the impact of these effects on the simulated spectra,
for different and column densities of the outflow. The observed optical
depth is usually considered a proxy for the wind , independently on its
velocity. However, our simulations show that the observed optical depth of an
outflow with a given column density decreases rapidly as the velocity of
the wind approaches relativistic values. This, in turn, implies that when
estimating from the optical depth, it is necessary to include a
velocity-dependent correction, already for moderate velocities (e.g. ). This correction linearly propagates to the derived . As an example of these effects, we calculate the
relativistically corrected values of and for a
sample of Ultra-Fast Outflows taken from the literature, and find
correction factors of within the observed range of outflowing
velocities.Comment: 6 pages, 5 figures. Accepted for publication in A&
Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy
Powerful winds driven by active galactic nuclei (AGN) are often invoked to
play a fundamental role in the evolution of both supermassive black holes
(SMBHs) and their host galaxies, quenching star formation and explaining the
tight SMBH-galaxy relations. Recent observations of large-scale molecular
outflows in ultra-luminous infrared galaxies (ULIRGs) have provided the
evidence to support these studies, as they directly trace the gas out of which
stars form. Theoretical models suggest an origin of these outflows as
energy-conserving flows driven by fast AGN accretion disk winds. Previous
claims of a connection between large-scale molecular outflows and AGN activity
in ULIRGs were incomplete because they were lacking the detection of the
putative inner wind. Conversely, studies of powerful AGN accretion disk winds
to date have focused only on X-ray observations of local Seyferts and a few
higher redshift quasars. Here we show the clear detection of a powerful AGN
accretion disk wind with a mildly relativistic velocity of 0.25c in the X-ray
spectrum of IRAS F11119+3257, a nearby (z = 0.189) optically classified type 1
ULIRG hosting a powerful molecular outflow. The AGN is responsible for ~80% of
the emission, with a quasar-like luminosity of L_AGN = 1.5x10^46 erg/s. The
energetics of these winds are consistent with the energy-conserving mechanism,
which is the basis of the quasar mode feedback in AGN lacking powerful radio
jets.Comment: Revised file including the letter, methods and supplementary
information. Published in the March 26th 2015 issue of Natur
Ferromagnetism in laser deposited anatase TiCoO_{2-\delta} films
Pulsed laser deposited films of Co doped anatase TiO2 are examined for Co
substitutionality, ferromagnetism, transport, magnetotransport and optical
properties. Our results show limited solubility (up to ~ 2 %) of Co in the
as-grown films and formation of Co clusters thereafter. For Ti0.93Co0.07O2-d
sample, which exhibits a Curie temperature (Tc) over 1180 K, we find the
presence of 20-50 nm Co clusters as well as a small concentration of Co
incorporated into the remaining matrix. After being subjected to the high
temperature anneal during the first magnetization measurement, the very same
sample shows a Tc ~ 650 K and almost full matrix incorporation of Co. This Tc
is close to that of as-grown Ti0.99Co0.01O2-d sample (~ 700 K). The transport,
magnetotransport and optical studies also reveal interesting effects of the
matrix incorporation of Co. These results are indicative of an intrinsic
Ti1-xCoxO2-d diluted magnetic semiconductor with Tc of about 650-700 K.Comment: 14 pages + 9 figure
Magnetization steps in Zn_(1-x)Mn_xO: Four largest exchange constants and single-ion anisotropy
Magnetization steps (MST's) from Mn pairs in several single crystals of
Zn_(1-x)Mn_xO (0.0056<=x<=0.030, and in one powder (x=0.029), were observed.
The largest two exchange constants, J1/kB=-18.2+/-0.5K and J1'/kB=-24.3+/-0.6K,
were obtained from large peaks in the differential susceptibility, dM/dH,
measured in pulsed magnetic fields, H, up to 500 kOe. These two largest J's are
associated with the two inequivalent classes of nearest neighbors (NN's) in the
wurtzite structure. The 29% difference between J1 and J1' is substantially
larger than 13% in CdS:Mn, and 15% in CdSe:Mn. The pulsed-field data also
indicate that, despite the direct contact between the samples and a
superfluid-helium bath, substantial departures from thermal equilibrium
occurred during the 7.4 ms pulse. The third- and fourth-largest J's were
determined from the magnetization M at 20 mK, measured in dc magnetic fields H
up to 90 kOe. Both field orientations H||c and H||[10-10] were studied. (The
[10-10] direction is perpendicular to the c-axis, [0001].) By definition,
neighbors which are not NN's are distant neighbors (DN's). The largest DN
exchange constant (third-largest overall), has the value J/kB=-0.543+/-0.005K,
and is associated with the DN at r=c. Because this is not the closest DN, this
result implies that the J's do not decrease monotonically with the distance r.
The second-largest DN exchange constant (fourth-largest overall), has the value
J/kB=-0.080 K. It is associated with one of the two classes of neighbors that
have a coordination number z=12, but the evidence is insufficient for a
definite unique choice. The dependence of M on the direction of H gives
D/kB=-0.039+/-0.008K, in fair agreement with -0.031 K from earlier EPR work.Comment: 12 pages, 10 figures. Submitted to PR
Usefulness of Simple Diffusion Kurtosis Imaging for Head and Neck Tumors: An Early Clinical Study
Diffusion kurtosis (DK) imaging (DKI), a type of restricted diffusion-weighted imaging, has been reported to be useful for tumor diagnoses in clinical studies. We developed a software program to simultaneously create DK images with apparent diffusion coefficient (ADC) maps and conducted an initial clinical study. Multi-shot echo-planar diffusion-weighted images were obtained at b-values of 0, 400, and 800 sec/mm2 for simple DKI, and DK images were created simultaneously with the ADC map. The usefulness of the DK image and ADC map was evaluated using a pixel analysis of all pixels and a median analysis of the pixels of each case. Tumor and normal tissues differed significantly in both pixel and median analyses. In the pixel analysis, the area under the curve was 0.64 for the mean kurtosis (MK) value and 0.77 for the ADC value. In the median analysis, the MK value was 0.74, and the ADC value was 0.75. The MK and ADC values correlated moderately in the pixel analysis and strongly in the median analysis. Our simple DKI system created DK images simultaneously with ADC maps, and the obtained MK and ADC values were useful for differentiating head and neck tumors from normal tissue
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