3,066 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
The collisional evolution of undifferentiated asteroids and the formation of chondritic meteoroids
Most meteorites are fragments from recent collisions experienced in the
asteroid belt. In such a hyper-velocity collision, the smaller collision
partner is destroyed, whereas a crater on the asteroid is formed or it is
entirely disrupted, too. The present size distribution of the asteroid belt
suggests that an asteroid with 100 km radius is encountered times
during the lifetime of the Solar System by objects larger than 10 cm in radius;
the formed craters cover the surface of the asteroid about 100 times. We
present a Monte Carlo code that takes into account the statistical bombardment
of individual infinitesimally small surface elements, the subsequent compaction
of the underlying material, the formation of a crater and a regolith layer. For
the entire asteroid, 10,000 individual surface elements are calculated. We
compare the ejected material from the calculated craters with the shock stage
of meteorites with low petrologic type and find that these most likely stem
from smaller parent bodies that do not possess a significant regolith layer.
For larger objects, which accrete a regolith layer, a prediction of the
thickness depending on the largest visible crater can be made. Additionally, we
compare the crater distribution of an object initially 100 km in radius with
the shape model of the asteroid (21) Lutetia, assuming it to be initially
formed spherical with a radius that is equal to its longest present ellipsoid
length. Here, we find the shapes of both objects to show resemblance to each
other.Comment: Accepted by Ap
Outlier Classification Criterion for Multivariate Cyber Anomaly Detection
Every day, intrusion detection systems catalogue millions of unsupervised data entries. This represents a “big data” problem for research sponsors within the Department of Defense. In a first response to this issue, raw data capture was transformed into usable vectors and an array of multivariate techniques implemented to detect potential outliers. This research expands and refines these techniques by implementing a Chi-Square Q-Q plot-based classification criteria for outlier detection. This methodology has been implemented into an R-based programming solution that allows for a refined and semi-automated user experience for intelligence analysts. Moreover, two case analyses are performed that illustrate how this methodology explicitly identifies outlier observations and provides formal multivariate normality testing to assess the reliability of the techniques being utilized
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
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