1,298 research outputs found
A catalogue sample of low mass galaxies observed in X-rays with central candidate black holes
We present a sample of -ray selected candidate black holes in 51 low mass
galaxies with {and mass up to M} obtained by
cross-correlating the NASA-SLOAN Atlas with the 3XMM catalogue. {We have also
searched in the available catalogues for radio counterparts of the black hole
candidates and find that 19 of the previously selected sources have also a
radio counterpart.} Our results show that about of the galaxies of our
sample host { an -ray source} (associated to a radio counterpart) spatially
coincident with the galaxy center, in agreement with { other recent works}. For
these {\it nuclear} sources, the -ray/radio fundamental plane relation
allows one to estimate the mass of the (central) candidate black holes which
results to be in the range M (with median
value of M and eight candidates having mass
below M). This result, while suggesting that -ray
emitting black holes in low-mass galaxies may have had a key role in the
evolution of such systems, makes even more urgent to explain how such massive
objects formed in galaxies. {Of course, dedicated follow-up observations both
in the -ray and radio bands, as well as in the optical, are necessary in
order to confirm our resultsComment: 15 Pages, 2 Figures, 3 Table
XMM-Newton observation of a sample of four close dSph galaxies
We present the results of the analysis of deep archival \sat\ observations
towards the dwarf spheroidal galaxies Draco, Leo I, Ursa Major II and Ursa
Minor in the Milky Way neighbourhood. The X-ray source population is
characterized and cross-correlated with available databases with the aim to
infer their nature. We also investigate if intermediate-mass black holes are
hosted in the center of these galaxies. In the case of Draco, we detect 96
high-energy sources, two of them being possibly local stars, while no evidence
for any X-ray emitting central compact object is found. Towards the Leo I and
UMa II field of view we reveal 116 and 49 X-ray sources, respectively. None of
them correlates with the putative central black holes and only one is likely
associated with a UMa II local source. The study of the UMi dwarf galaxy shows
54 high-energy sources and a possible association {with a source at the dSph
center}. We put an upper limit to the central compact object luminosity of
4.0210 erg/s. Furthermore, via the correlation with a radio
source near the galactic center, we get that the putative black hole should
have a mass of and be
radiatively inefficient. This confirms a previous result obtained by using
Chandra data alone.Comment: MNRAS, in press, tables available on lin
Astrometric microlensing
Astrometric microlensing will offer in the next future a new channel for
investigating the nature of both lenses and sources involved in a gravitational
microlensing event. The effect, corresponding to the shift of the position of
the multiple image centroid with respect to the source star location, is
expected to occurr on scales from micro-arcoseconds to milli-arcoseconds
depending on the characteristics of the lens-source system. Here, we consider
different classes of events (single/binary lens acting on a single/binary
source) also accounting for additional effects including the finite source
size, the blending and orbital motion. This is particularly important in the
era of Gaia observations which is making possible astrometric measurements with
unprecedent quality.Comment: On IJMP D, 15 pages, 6 Figure
Life history and ecological genetics of the colonial ascidian Botryllus schlosseri
The colonial ascidian Botryllus schlosseri is a cosmopolitan, marine filter feeder, introduced as a laboratory research
organism in the 1950s. Currently, it is widely used in many laboratories to investigate a variety of biological questions.
Recently, it has become a species of concern, as it is an invasive species in many coastal environments. Here, we review
studies on the geographical distribution of the species, sexual and asexual reproduction in the field, tolerance to
temperature, salinity and anthropogenic activity, polychromatism, enzymatic polymorphism, and the genetic basis of
pigmentation. Studying the relationship between genetic polymorphism and the adaptation of B. schlosseri to
environmental stress is a challenge of future research and will improve our understanding of its evolutionary success
and invasive potential
Investigation of unconventional reconstruction and electronic properties on the Na2IrO3 surface
Na2IrO3 is an intriguing material for which spin-orbit coupling plays a key
role. Theoretical predictions, so far unverified, have been made that the
surface of Na2IrO3 should exhibit a clear signature of the quantum spin Hall
effect. We studied the surface of Na2IrO3 using scanning tunneling microscopy
and density-functional theory calculations. We observed atomic level resolution
of the surface and two types of terminations with different surface periodicity
and Na content. By comparing bias-dependent experimental topographic images to
simulated images, we determined the detailed atomistic structure of both
observed surfaces. One of these reveals a strong relaxation to the surface of
Na atoms from the subsurface region two atomic layers below. Such dramatic
structural changes at the surface cast doubt on any prediction of surface
properties based on bulk electronic structure. Indeed, using spatially resolved
tunneling spectroscopy we found no indication of the predicted quantum spin
Hall behavior
Spontaneous Pattern Formation in a Polariton Condensate
Polariton condensation can be regarded as a self-organization phenomenon,
where phase ordering is established among particles in the system. In such
condensed systems, further ordering can possibly occur in the particle density
distribution, under particular experimental conditions. In this work we report
on spontaneous pattern formation in a polariton condensate under non-resonant
optical pumping. The slightly elliptical ring-shaped excitation laser we employ
is such to force condensation to occur in a single-energy state with periodic
boundary conditions, giving rise to a multi-lobe standing wave patterned state
Isogeometric Analysis in advection-diffusion problems: tension splines approximation
We present a novel approach, within the new paradigm of isogeometric analysis
introduced by Hughes et al., to deal with advection dominated
advection-diffusion problems. The key ingredient is the use of Galerkin approximating
spaces of functions with high smoothness, as in IgA based on
classical B-splines, but particularly well suited to describe sharp layers involving
very strong gradients
Penrose-Onsager Criterion Validation in a One-Dimensional Polariton Condensate
We perform quantum tomography on one-dimensional polariton condensates,
spontaneously occurring in linear disorder valleys in a CdTe planar microcavity
sample. By the use of optical interferometric techniques, we determine the
first-order coherence function and the amplitude and phase of the order
parameter of the condensate, providing a full reconstruction of the single
particle density matrix for the polariton system. The experimental data are
used as input to theoretically test the consistency of Penrose-Onsager
criterion for Bose-Einstein condensation in the framework of nonequilibrium
polariton condensates. The results confirm the pertinence and validity of the
criterion for a non equilibrium condensed gas.Comment: 5 pages, 4 figure
The puzzling symbiotic X-ray system 4U1700+24
Symbiotic X-ray binaries form a subclass of low-mass X-ray binary systems
consisting of a neutron star accreting material from a red giant donor star via
stellar wind or Roche lobe overflow. Only a few confirmed members are currently
known; 4U 1700+24 is a good candidate as it is a relatively bright X-ray
object, possibly associated with the late-type star V934 Her. We analysed the
archive {\it XMM}-Newton and Swift/XRT observations of 4U 1700+24 in order to
have a uniform high-energy ( keV) view of the source. We confirmed the
existence of a red-shifted O VIII Ly- transition (already observed in
the 2002 {\it XMM}-Newton data) in the high-resolution spectra collected via
the RGS instruments. The red-shift of the line is found in all the analysed
observations and, on average, it was estimated to be . We also
observed a modulation of the centroid energy of the line on short time scales
(a few days) and discuss the observations in the framework of different
scenarios. If the modulation is due to the gravitational red-shift of the
neutron star, it might arise from a sudden re-organization of the emitting
-ray matter on the scale of a few hundreds of km. Alternatively, we are
witnessing a uni-polar jet of matter (with typical velocity of km
s) possibly emitted by the neutron star in an almost face-on system. The
second possibility seems to be required by the apparent lack of any modulation
in the observed -ray light curve. We also note also that the low-resolution
spectra (both {\it XMM}-Newton and Swift/XRT in the keV band) show the
existence of a black body radiation emitted by a region (possibly associated
with the neutron star polar cap) with typical size from a few tens to hundreds
of meters. The size of this spot-like region reduces as the overall luminosity
of 4U 1700+24 decreases.Comment: In press on A&
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