7,163 research outputs found
The distribution and abundance of the inarticulate brachiopod Glottidia albida (Hinds) on the mainland shelf of southern California
Around 200 new X-ray binary IDs from 13 years of Chandra observations of the M31 center
We have created 0.3--10 keV, 13 year, unabsorbed luminosity lightcurves for
528 X-ray sources in the central 20' of M31. We have 174 Chandra observations
spaced at ~1 month intervals thanks to our transient monitoring program, deeper
observations of the M31 nucleus, and some public data from other surveys. We
created 0.5--4.5 keV structure functions (SFs) for each source, for comparison
with the ensemble structure function of AGN. We find 220 X-ray sources with
luminosities > ~1E+35 erg/s that have SFs with significantly more variability
than the ensemble AGN SF, and are likely X-ray binaries (XBs). A further 30
X-ray sources were identified as XBs using other methods. We therefore have 250
probable XBs in total, including ~200 new identifications. This result
represents great progress over the ~50 XBs and ~40 XB candidates previously
identified out of the ~2000 X-ray sources within the D_25 region of M31; it
also demonstrates the power of SF analysis for identifying XBs in external
galaxies. We also identify a new transient black hole candidate, associated
with the M31 globular cluster B128.Comment: Accepted for publication in ApJ; 20 pages, 7 figures; Tables 1 and 2
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Interactive volumetric segmentation for textile micro-tomography data using wavelets and nonlocal means
This work addresses segmentation of volumetric images of woven carbon fiber textiles from micro-tomography data. We propose a semi-supervised algorithm to classify carbon fibers that requires sparse input as opposed to completely labeled images. The main contributions are: (a) design of effective discriminative classifiers, for three-dimensional textile samples, trained on wavelet features for segmentation; (b) coupling of previous step with nonlocal means as simple, efficient alternative to the Potts model; and (c) demonstration of reuse of classifier to diverse samples containing similar content. We evaluate our work by curating test sets of voxels in the absence of a complete ground truth mask. The algorithm obtains an average 0.95 F1 score on test sets and average F1 score of 0.93 on new samples. We conclude with discussion of failure cases and propose future directions toward analysis of spatiotemporal high-resolution micro-tomography images
Energy-dependent evolution in IC10 X-1: hard evidence for an extended corona and implications
We have analyzed a ~130 ks XMM-Newton observation of the dynamically confirmed black hole + Wolf-Rayet (BH+WR) X-ray binary (XB) IC10 X-1, covering ~1 orbital cycle. This system experiences periodic intensity dips every ~35 hr. We find that energy-independent evolution is rejected at a >5Ï level. The spectral and timing evolution of IC10 X-1 are best explained by a compact disk blackbody and an extended Comptonized component, where the thermal component is completely absorbed and the Comptonized component is partially covered during the dip. We consider three possibilities for the absorber: cold material in the outer accretion disk, as is well documented for Galactic neutron star (NS) XBs at high inclination; a stream of stellar wind that is enhanced by traveling through the L1 point; and a spherical wind. We estimated the corona radius (r ADC) for IC10 X-1 from the dip ingress to be ~106 km, assuming absorption from the outer disk, and found it to be consistent with the relation between r ADC and 1-30 keV luminosity observed in Galactic NS XBs that spans two orders of magnitude. For the other two scenarios, the corona would be larger. Prior BH mass (M BH) estimates range over 23-38 M â, depending on the inclination and WR mass. For disk absorption, the inclination, i, is likely to be ~60-80°, with M BH ~ 24-41 M â. Alternatively, the L1-enhanced wind requires i ~ 80°, suggesting ~24-33 M â. For a spherical absorber, i ~ 40°, and M BH ~ 50-65 M â
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Predicting space climate change
The recent decline in the open magnetic flux of the Sun heralds the end of the Grand Solar Maximum (GSM) that has persisted throughout the space age, during which the largestâfluence Solar Energetic Particle (SEP) events have been rare and Galactic Cosmic Ray (GCR) fluxes have been relatively low. In the absence of a predictive model of the solar dynamo, we here make analogue forecasts by studying past variations of solar activity in order to evaluate how longâterm change in space climate may influence the hazardous energetic particle environment of the Earth in the future. We predict the probable future variations in GCR flux, nearâEarth interplanetary magnetic field (IMF), sunspot number, and the probability of large SEP events, all deduced from cosmogenic isotope abundance changes following 24 GSMs in a 9300âyear record
Time variability of X-ray sources in the M 31 centre field
We present an extension to our XMM-Newton X-ray source catalogue of M 31,
containing 39 newly found sources. In order to classify and identify more of
the sources we search for X-ray time variability in XMM-Newton archival data of
the M 31 centre field.
As a source list we used our extended catalogue based on observations
covering the time span from June 2000 to July 2004. We then determined the flux
or at least an upper limit at the source positions for each observation.
Deriving the flux ratios for the different observations and searching for the
maximum flux difference we determined variability factors. We also calculated
the significance of the flux ratios.
Using hardness ratios, X-ray variability and cross correlations with
catalogues in the X-ray, optical, infrared and radio regimes, we detected three
super soft source candidates, one supernova remnant and six supernova remnant
candidates, one globular cluster candidate, three X-ray binaries and four X-ray
binary candidates. Additionally we identified one foreground star candidate and
classified fifteen sources with hard spectra, which may either be X-ray
binaries or Crab-like supernova remnants in M 31 or background active galactic
nuclei. The remaining five sources stay unidentified or without classification.
Based on the time variability results we suggest six sources, which were
formerly classified as "hard", to be X-ray binary candidates. The
classification of one other source (XMMM31 J004236.7+411349) as a supernova
remnant, has to be rejected due to the distinct time variability we found. We
now classify this source as a foreground star.Comment: 13 pages, 6 figures, accepted for publication in A&
Four new black hole candidates identified in M31 globular clusters with Chandra and XMM-Newton
We have identified four new black hole candidates in M31 globular clusters
using 123 Chandra, and 4 XMM-Newton observations of the M31 central region. The
X-ray source associated with Bo 163 (XB163) is a recurrent transient, with the
highest luminosity ~1.4E+38 erg/s, considerably brighter than any outbursts
from the neutron star transients Aql X-1 or 4U 1608-452; the outburst
apparently started ~45 days earlier than the observed peak, hence the
luminosity could have been considerably higher. We identified XB082, XB153 and
XB185 as BHCs by observing "low state" emission spectra at luminosities that
exceed the threshold for neutron star binaries. The probability that these are
neutron star systems with anisotropic emission beamed toward us is <4E-4, and
their variability suggests emission from a single source. We therefore conclude
that these systems likely contain black holes rather than neutron stars. We
have now identified 4 persistently bright BHCs in the region; the probability
that these are all background AGN is <1E-20. According to theory, the donors
could be tidally captured main sequence stars, or white dwarves in
ultra-compact binaries. We find that GCs that are particularly massive (XB082)
or metal rich (XB144) can host bright X-ray sources in addition to those that
are both (XB163). Our method may reveal BHCs in other bright X-ray sources.Comment: Accepted for publication in ApJ. 17 pages, 5 figure
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