450 research outputs found
The origin of seed photons for Comptonization in the black hole binary Swift J1753.5-0127
Aims. The black hole binary SWIFT J1753.5-0127 is providing a unique data set
to study accretion flows. Various investigations of this system and of other
black holes have not, however, led to an agreement on the accretion flow
geometry or on the seed photon source for Comptonization during different
stages of X-ray outbursts. We place constraints on these accretion flow
properties by studying long-term spectral variations of this source. Methods.
We performed phenomenological and self-consistent broad band spectral modeling
of Swift J1753.5-0127 using quasi-simultaneous archived data from
INTEGRAL/ISGRI, Swift/UVOT/XRT/BAT, RXTE/PCA/HEXTE and MAXI/GSC instruments.
Results. We identify a critical flux limit, F \sim 1.5 \times 10^{-8}
erg/cm^2/s, and show that the spectral properties of SWIFT J1753.5-0127 are
markedly different above and below this value. Above the limit, during the
outburst peak, the hot medium seems to intercept roughly 50 percent of the disk
emission. Below it, in the outburst tail, the contribution of the disk photons
reduces significantly and the entire spectrum from the optical to X-rays can be
produced by a synchrotron-self-Compton mechanism. The long-term variations in
the hard X-ray spectra are caused by erratic changes of the electron
temperatures in the hot medium. Thermal Comptonization models indicate
unreasonably low hot medium optical depths during the short incursions into the
soft state after 2010, suggesting that non-thermal electrons produce the
Comptonized tail in this state. The soft X-ray excess, likely produced by the
accretion disk, shows peculiarly stable temperatures for over an order of
magnitude changes in flux. Conclusions. The long-term spectral trends of SWIFT
J1753.5-0127 are likely set by variations of the truncation radius and a
formation of a hot, quasi-spherical inner flow in the vicinity of the black
hole. (abridged)Comment: 16 pages, 8 figures, published in A&
Searching for X-ray sources in nearby late-type galaxies with low star formation rates
Late type non-starburst galaxies have been shown to contain X-ray emitting
objects, some being ultraluminous X-ray sources. We report on XMM-Newton
observations of 11 nearby, late-type galaxies previously observed with the
Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray
sources in or near the optical extent of the galaxies, most being point-like.
If associated with the corresponding galaxies, the source luminosities range
from erg s to erg s. We
found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one
source coincident with the galaxy IC 4662 with a blackbody temperature of
keV that could be a quasi-soft source or a quiescent neutron
star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0691316,
is extended and coincident with a galaxy cluster visible on an HST image. The
X-ray spectrum of the cluster reveals a redshift of and a
temperature of 3.60.4 keV. The redshift was mainly determined by a cluster
of Fe XXIV lines between the observed energy range keV.Comment: 8 pages, to appear in MNRA
Expanding hot flow in the black hole binary SWIFT J1753.5-0127: evidence from optical timing
We describe the evolution of optical and X-ray temporal characteristics
during the outburst decline of the black hole X-ray binary SWIFT J1753.5-0127.
The optical/X-ray cross-correlation function demonstrates a single positive
correlation at the outburst peak, then it has multiple dips and peaks during
the decline stage, which are then replaced by the precognition dip plus peak
structure in the outburst tail. Power spectral densities and phase lags show a
complex evolution, revealing the presence of intrinsically connected optical
and X-ray quasi-periodic oscillations. For the first time, we quantitatively
explain the evolution of these timing properties during the entire outburst
within one model, the essence of which is the expansion of the hot accretion
flow towards the tail of the outburst. The pivoting of the spectrum produced by
synchrotron Comptonization in the hot flow is responsible for the appearance of
the anti-correlation with the X-rays and for the optical quasi-periodic
oscillations. Our model reproduces well the cross-correlation and phase lag
spectrum during the decline stage, which could not be understood with any model
proposed before.Comment: 13 pages, 11 figures, MNRAS submitte
REPETITA: detection and discrimination of the periodicity of protein solenoid repeats by discrete Fourier transform
Motivation: Proteins with solenoid repeats evolve more quickly than non-repetitive ones and their periodicity may be rapidly hidden at sequence level, while still evident in structure. In order to identify these repeats, we propose here a novel method based on a metric characterizing amino-acid properties (polarity, secondary structure, molecular volume, codon diversity, electric charge) using five previously derived numerical functions
Creating a Dataset for Multilingual Fine-grained Emotion-detection Using Gamification-based Annotation
This paper introduces a gamified framework for fine-grained sentiment analysis and emotion detection. We present a flexible tool, Sentimentator, that can be used for efficient annotation based on crowd sourcing and a selfperpetuating gold standard. We also present a novel dataset with multi-dimensional annotations of emotions and sentiments in movie subtitles that enables research on sentiment preservation across languages and the creation of robust multilingual emotion detection tools. The tools and datasets are public and opensource and can easily be extended and applied for various purposes.Peer reviewe
The December 2015 re-brightening of V404 Cyg: Variable absorption from the accretion disc outflow
In December 2015 the black hole binary V404 Cyg underwent a secondary
outburst after the main June 2015 event. We monitored this re-brightening with
the INTEGRAL and Swift satellites, and in this paper we report the results of
the time-resolved spectral analysis of these data. The December outburst shared
similar characteristics with the June one. The well sampled INTEGRAL light
curve shows up to 10 Crab flares, which are separated by relatively weak
non-flaring emission phases when compared to the June outburst. The spectra are
well described by absorbed Comptonization models, with hard photon indices,
, and significant detections of a high-energy cut-off only
during the bright flares. This is in contrast to the June outburst, where the
Comptonization models gave electron temperatures mostly in the 30--50 keV
range, while some spectra were soft () without signs of any
spectral cut-off. Similarly to the June outburst, we see clear sings of a
variable local absorber in the soft energy band covered by Swift/XRT and
INTEGRAL/JEM-X, which causes rapid spectral variations observed during the
flares. During one flare, both Swift and INTEGRAL captured V404 Cyg in a state
where the absorber was nearly Compton thick, , and the broad band spectrum was similar to obscured
AGN spectra, as seen during the "plateaus" in the June outburst. We conclude
that the spectral behaviour of V404 Cyg during the December outburst was
analogous with the first few days of the June outburst, both having hard X-ray
flares that were intermittently influenced by obscuration due to nearly
Compton-thick outflows launched from the accretion disc.Comment: 9 pages, 6 figures, accepted to A&
Rapid spectral transition of the black hole binary V404 Cyg
During the June 2015 outburst of the black hole binary V404 Cyg, rapid
changes in the X-ray brightness and spectra were common. The INTEGRAL
monitoring campaign detected spectacular Eddington-limited X-ray flares, but
also rapid variations at much lower flux levels. On 2015 June 21 at 20 h 50
min, the 3-10 keV JEM-X data as well as simultaneous optical data started to
display a gradual brightening from one of these low-flux states. This was
followed 15 min later by an order-of-magnitude increase of flux in the 20-40
keV IBIS/ISGRI light curve in just 15 s. The best-fitting model for both the
pre- and post-transition spectra required a Compton-thick partially covering
absorber. The absorber parameters remained constant, but the spectral slope
varied significantly during the event, with the photon index decreasing from
to . We propose that the rapid 20-40
keV flux increase was either caused by a spectral state transition that was
hidden from our direct view, or that there was a sudden reduction in the amount
of Compton down-scattering of the primary X-ray emission in the disk outflow.Comment: 6 pages, 2 figures, accepted to A&
The repetitive structure of DNA clamps: An overlooked protein tandem repeat
Structured tandem repeats proteins (STRPs) are a specific kind of tandem repeat proteins characterized by a modular and repetitive three-dimensional structure arrangement. The majority of STRPs adopt solenoid structures, but with the increasing availability of experimental structures and high-quality predicted structural models, more STRP folds can be characterized. Here, we describe “Box repeats”, an overlooked STRP fold present in the DNA sliding clamp processivity factors, which has eluded classification although structural data has been available since the late 1990s. Each Box repeat is a β⍺βββ module of about 60 residues, which forms a class V “beads-on-a-string” type STRP. The number of repeats present in processivity factors is organism dependent. Monomers of PCNA proteins in both Archaea and Eukarya have 4 repeats, while the monomers of bacterial beta-sliding clamps have 6 repeats. This new repeat fold has been added to the RepeatsDB database, which now provides structural annotation for 66 Box repeat proteins belonging to different organisms, including viruses
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