282 research outputs found
The two Ultraluminous X-ray sources in the galaxy NGC 925
NGC 925 ULX-1 and ULX-2 are two ultraluminous X-ray sources in the galaxy NGC
925, at a distance of 8.5 Mpc. For the first time, we analyzed high quality,
simultaneous XMM-Newton and NuSTAR data of both sources. Although at a first
glance ULX-1 resembles an intermediate mass black hole candidate (IMBH) because
of its high X-ray luminosity ( erg s) and its
spectral/temporal features, a closer inspection shows that its properties are
more similar to those of a typical super-Eddington accreting stellar black hole
and we classify it as a `broadened disc' ultraluminous X-ray source. Based on
the physical interpretation of this spectral state, we suggest that ULX-1 is
seen at small inclination angles, possibly through the evacuated cone of a
powerful wind originating in the accretion disc. The spectral classification of
ULX-2 is less certain, but we disfavour an IMBH accreting at sub-Eddington
rates as none of its spectral/temporal properties can be associated to either
the soft or hard state of Galactic accreting black hole binaries.Comment: Accepted on MNRAS with very minor comments, 7 pages, 5 figures, 1
tabl
Deep panoramic depth prediction and completion for indoor scenes
We introduce a novel end-to-end deep-learning solution for rapidly estimating a dense spherical depth map of an indoor environment. Our input is a single equirectangular image registered with a sparse depth map, as provided by a variety of common capture setups. Depth is inferred by an efficient and lightweight single-branch network, which employs a dynamic gating system to process together dense visual data and sparse geometric data. We exploit the characteristics of typical man-made environments to efficiently compress multi-resolution features and find short- and long-range relations among scene parts. Furthermore, we introduce a new augmentation strategy to make the model robust to different types of sparsity, including those generated by various structured light sensors and LiDAR setups. The experimental results demonstrate that our method provides interactive performance and outperforms state-of-the-art solutions in computational efficiency, adaptivity to variable depth sparsity patterns, and prediction accuracy for challenging indoor data, even when trained solely on synthetic data without any fine tuning. (Figure presented.
Behind the dust curtain: the spectacular case of GRB 160623A
We report on the X-ray dust-scattering features observed around the afterglow
of the gamma ray burst GRB 160623A. With an XMM-Newton observation carried out
~2 days after the burst, we found evidence of at least six rings, with angular
size expanding between ~2 and 9 arcmin, as expected for X-ray scattering of the
prompt GRB emission by dust clouds in our Galaxy. From the expansion rate of
the rings, we measured the distances of the dust layers with extraordinary
precision: 528.1 +\- 1.2 pc, 679.2 +\- 1.9 pc, 789.0 +\- 2.8 pc, 952 +\- 5 pc,
1539 +\- 20 pc and 5079 +\- 64 pc. A spectral analysis of the ring spectra,
based on an appropriate dust-scattering model (BARE-GR-B from Zubko et al.
2004}) and the estimated burst fluence, allowed us to derive the column density
of the individual dust layers, which are in the range 7x10^20-1.5x10^22 cm^-2.
The farthest dust-layer (i.e. the one responsible for the smallest ring) is
also the one with the lowest column density and it is possibly very extended,
indicating a diffuse dust region. The properties derived for the six
dust-layers (distance, thickness, and optical depth) are generally in good
agreement with independent information on the reddening along this line of
sight and on the distribution of molecular and atomic gas.Comment: 9 pages, 10 figures, 1 table; accepted for publication in MNRA
Efficient computation of bifurcation diagrams with a deflated approach to reduced basis spectral element method
The majority of the most common physical phenomena can be described using partial differential equations (PDEs). However, they are very often characterized by strong nonlinearities. Such features lead to the coexistence of multiple solutions studied by the bifurcation theory. Unfortunately, in practical scenarios, one has to exploit numerical methods to compute the solutions of systems of PDEs, even if the classical techniques are usually able to compute only a single solution for any value of a parameter when more branches exist. In this work, we implemented an elaborated deflated continuation method that relies on the spectral element method (SEM) and on the reduced basis (RB) one to efficiently compute bifurcation diagrams with more parameters and more bifurcation points. The deflated continuation method can be obtained combining the classical continuation method and the deflation one: the former is used to entirely track each known branch of the diagram, while the latter is exploited to discover the new ones. Finally, when more than one parameter is considered, the efficiency of the computation is ensured by the fact that the diagrams can be computed during the online phase while, during the offline one, one only has to compute one-dimensional diagrams. In this work, after a more detailed description of the method, we will show the results that can be obtained using it to compute a bifurcation diagram associated with a problem governed by the Navier-Stokes equations
A possible cyclotron resonance scattering feature near 0.7 keV in X1822-371
We analyse all available X-ray observations of X1822-371 made with
XMM-Newton, Chandra, Suzaku and INTEGRAL satellites. The observations were not
simultaneous. The Suzaku and INTEGRAL broad band energy coverage allows us to
constrain the spectral shape of the continuum emission well. We use the model
already proposed for this source, consisting of a Comptonised component
absorbed by interstellar matter and partially absorbed by local neutral matter,
and we added a Gaussian feature in absorption at keV. This addition
significantly improves the fit and flattens the residuals between 0.6 and 0.8
keV. We interpret the Gaussian feature in absorption as a cyclotron resonant
scattering feature (CRSF) produced close to the neutron star surface and derive
the magnetic field strength at the surface of the neutron star, G for a radius of 10 km. We derive the pulse period in the
EPIC-pn data to be 0.5928850(6) s and estimate that the spin period derivative
of X1822-371 is s/s using all available
pulse period measurements. Assuming that the intrinsic luminosity of
X1822-371is at the Eddington limit and using the values of spin period and spin
period derivative of the source, we constrain the neutron star and companion
star masses. We find the neutron star and the companion star masses to be M and M, respectively, for a
neutron star radius of 10 km.In a self-consistent scenario in which X1822-371
is spinning-up and accretes at the Eddington limit, we estimate that the
magnetic field of the neutron star is G for a
neutron star radius of 10 km. If our interpretation is correct, the Gaussian
absorption feature near 0.7 keV is the very first detection of a CRSF below 1
keV in a LMXB. (abridged)Comment: 14 pages, 12 figures, accepted for publication in A&
GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary
The bursting pulsar, GRO J1744-28, went again in outburst after 18
years of quiescence in mid-January 2014. We studied the broad-band, persistent,
X-ray spectrum using X-ray data from a XMM-Newton observation, performed almost
at the peak of the outburst, and from a close INTEGRAL observation, performed 3
days later, thus covering the 1.3-70.0 keV band. The spectrum shows a complex
continuum shape that cannot be modelled with standard high-mass X-ray pulsar
models, nor by two-components models. We observe broadband and peaked residuals
from 4 to 15 keV, and we propose a self-consistent interpretation of these
residuals, assuming they are produced by cyclotron absorption features and by a
moderately smeared, highly ionized, reflection component. We identify the
cyclotron fundamental at 4.7 keV, with hints for two possible harmonics
at 10.4 keV and 15.8 keV. The position of the cyclotron fundamental allows an
estimate for the pulsar magnetic field of (5.27 0.06) 10
G, if the feature is produced at its surface. From the dynamical and
relativistic smearing of the disk reflected component, we obtain a lower limit
estimate for the truncated accretion disk inner radius, ( 100 R),
and for the inclination angle (18-48). We also detect the
presence of a softer thermal component, that we associate with the emission
from an accretion disk truncated at a distance from the pulsar of 50-115 R.
From these estimates, we derive the magneto-spheric radius for disk accretion
to be 0.2 times the classical Alfv\'en radius for radial accretion.Comment: Accepted for publication in MNRA
Fibroblast proliferation and migration in wound healing by phytochemicals: Evidence for a novel synergic outcome
Wound-healing is a dynamic skin reparative process that results in a sequence of events, including inflammation, proliferation, and migration of different cell types as fibroblasts. Fibroblasts play a crucial role in repairing processes, from the late inflammatory phase until the fully final epithelization of the injured tissue. Within this context, identifying tools able to implement cell proliferation and migration could improve tissue regeneration. Recently, plants species from all over the world are coming out as novel tools for therapeutic applications thanks to their phytochemicals, which have antioxidant properties and can promote wound healing. In this paper, we aimed at investigating antioxidant activity of waste extracts from different medicinal plants, endemic of the Mediterranean area, on fibroblast proliferation and wound healing. We determined the amount of total phenols and anti-oxidant activity by ABTS assay. We then evaluated the cytotoxicity of the compounds and the proliferative capabilities of fibroblasts by scratch assay. Our results showed that waste extracts retain antioxidant and regenerative properties, inducing tissue re-establishment after environmental stress exposure. Taken together, our findings suggest that waste material could be used in the future also in combinations to stimulate wound healing processes and antioxidant responses in damaged skin
Signature of the presence of a third body orbiting around XB 1916-053
The ultra-compact dipping source \object{XB 1916-053} has an orbital period
of close to 50 min and a companion star with a very low mass (less than 0.1
M). The orbital period derivative of the source was estimated to be
s/s through analysing the delays associated with the
dip arrival times obtained from observations spanning 25 years, from 1978 to
2002. The known orbital period derivative is extremely large and can be
explained by invoking an extreme, non-conservative mass transfer rate that is
not easily justifiable. We extended the analysed data from 1978 to 2014, by
spanning 37 years, to verify whether a larger sample of data can be fitted with
a quadratic term or a different scenario has to be considered. We obtained 27
delays associated with the dip arrival times from data covering 37 years and
used different models to fit the time delays with respect to a constant period
model.We find that the quadratic form alone does not fit the data. The data are
well fitted using a sinusoidal term plus a quadratic function or,
alternatively, with a series of sinusoidal terms that can be associated with a
modulation of the dip arrival times due to the presence of a third body that
has an elliptical orbit. We infer that for a conservative mass transfer
scenario the modulation of the delays can be explained by invoking the presence
of a third body with mass between 0.10-0.14 M, orbital period around
the X-ray binary system of close to 51 yr and an eccentricity of . In a non-conservative mass transfer scenario we estimate that the
fraction of matter yielded by the degenerate companion star and accreted onto
the neutron star is , the neutron star mass is
M, and the companion star mass is 0.028 M. (Abridged)Comment: 13 pages, 9 figures. Accepted for publication in A&
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