187 research outputs found
Evidence of two unique variability classes from IGR J17091-3624
IGR J17091-3624 is the second black hole X-ray binary after GRS 1915+105,
which showed large and distinct variabilities. The study of these variability
classes can be useful to understand the accretion-ejection mechanisms of
accreting black holes, and hence to probe the strong gravity regime. We report
the discovery of two new variability classes (C1 and C2) from IGR J17091-3624
from the 2011 outburst Rossi X-ray Timing Explorer data. These unique classes
will be useful to have complete details about the source, and to learn new
aspects about variabilities. For examples, the C1 class shows that the
intensity and period of oscillations, energy spectrum and power spectrum can
clearly evolve in tens of seconds. Moreover, in such a small time scale,
soft-lag becomes hard-lag. The C2 class shows that the variability and the
nonvariability can occur at similar energy spectrum, and a soft state is not
required for variability to happen.Comment: 5 pages, 6 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
Properties of unique hard X-ray dips observed from GRS 1915+105 and IGR J17091-3624 and their implications
We report a comprehensive study on spectral and timing properties of hard
X-ray dips uniquely observed in some so-called variability classes of the
micro-quasars GRS 1915+105 and IGR J17091-3624. These dips are characterized by
a sudden decline in the 2.0-60.0 keV X-ray intensity by a factor of 4-12
simultaneous with the increase in hardness ratio by a factor of 2-4. Using 31
observations of GRS 1915+105 with RXTE/PCA, we show that different behavior are
observed in different types of variability classes, and we find that a
dichotomy is observed between classes with abrupt transitions vs those with
smoother evolution. For example, both energy-lag spectra and frequency-lag
spectra of hard X-ray dips in classes with abrupt transitions and shorter dip
intervals show hard-lag (hard photons lag soft photons), while both lag spectra
during hard dips in classes with smoother evolution and longer dip intervals
show soft-lag. Both lag time-scales are of the order of 100-600 msec. We also
show that timing and spectral properties of hard X-ray dips observed in light
curves of IGR J17091-3624 during its 2011 outburst are consistent with the
properties of the abrupt transitions in GRS 1915+105 rather than smooth
evolution. A global correlation between the X-ray intensity cycle time and hard
dip time is observed for both abrupt and smooth transition which may be due to
two distinct physical processes whose time-scales are eventually correlated. We
discuss implications of our results in the light of some generic models.Comment: 17 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Broadband X-ray emission and the reality of the broad iron line from the Neutron Star - White Dwarf X-ray binary 4U 1820-30
Broad relativistic iron lines from neutron star X-ray binaries are important
probes of the inner accretion disk. The X-ray reflection features can be
weakened due to strong magnetic fields or very low iron abundances such as is
possible in X-ray binaries with low mass, first generation stars as companions.
Here we investigate the reality of the broad iron line detected earlier from
the neutron star low mass X-ray binary 4U~1820--30 with a degenerate helium
dwarf companion. We perform a comprehensive, systematic broadband spectral
study of the atoll source using \suzaku{} and simultaneous \nustar{} \&
\swift{} observations. We have used different continuum models involving
accretion disk emission, thermal blackbody and thermal Comptonization of either
disk or blackbody photons. The \suzaku{} data show positive and negative
residuals in the region of iron K band. These features are well described by
two absorption edges at 7.67\pm0.14\kev and 6.93\pm0.07\kev or partial
covering photoionized absorption or by blurred reflection. Though, the
simultaneous \swift{} and \nustar{} data do not clearly reveal the emission or
absorption features, the data are consistent with the presence of either
absorption or emission features. Thus, the absorption based models provide an
alternative to the broad iron line or reflection model. The absorption features
may arise in winds from the inner accretion disk. The broadband spectra appear
to disfavour continuum models in which the blackbody emission from the neutron
star surface provides the seed photons for thermal Comptonization. Our results
suggest emission from a thin accretion disk (kT_{disk} \sim 1\kev),
Comptonization of disk photons in a boundary layer most likely covering a large
fraction of the neutron star surface and innermost parts of the accretion disk,
and blackbody emission (kT_{bb} \sim 2\kev) from the polar regions.Comment: 12 pages, 8 figures, 5 tables. Accepted for publication in MNRA
Climate risk and food security in Nepal—analysis of climate impacts on food security and livelihoods
Food security in Nepal is highly sensitive to climate risks. Recent climate-related events, such as the floods of 2008 and the winter drought of 2008/2009, have highlighted the potential impacts of climate on food production, access to markets and income from agricultural activities. However, the ways in which livelihoods and other vulnerabilities are linked to climate have not been well studied. The purpose of this analysis is to quantitatively and qualitatively assess climate (including climate variability, change and extremes) impacts on food security and livelihoods. The analytical method carried out for this research consisted of three components: (i) a dynamic analysis to evaluate the relationship between historic and current climatic variability and food security indicators, using long-term historical data; (ii) a descriptive analysis to establish a baseline against which vulnerability to future risks can be assessed, using household data from the Nepal Living Standards Survey 2010/2011 (NLSS-III); and (iii) a workshop with national stakeholders to validate the results and identify priority adaptation interventions
Potential T cell epitopes of Mycobacterium tuberculosis that can instigate molecular mimicry against host: implications in autoimmune pathogenesis
<p>Abstract</p> <p>Background</p> <p>Molecular mimicry between microbial antigens and host-proteins is one of the etiological enigmas for the occurrence of autoimmune diseases. T cells that recognize cross-reactive epitopes may trigger autoimmune reactions. Intriguingly, autoimmune diseases have been reported to be prevalent in tuberculosis endemic populations. Further, association of <it>Mycobacterium tuberculosis (M. tuberculosis) </it>has been implicated in different autoimmune diseases, including rheumatoid arthritis and multiple sclerosis. Although, <it>in silico </it>analyses have identified a number of <it>M. tuberculosis </it>specific vaccine candidates, the analysis on prospective cross-reactive epitopes, that may elicit autoimmune response, has not been yet attempted. Here, we have employed bioinformatics tools to determine T cell epitopes of homologous antigenic regions between <it>M. tuberculosis </it>and human proteomes.</p> <p>Results</p> <p>Employing bioinformatics tools, we have identified potentially cross-reactive T cell epitopes restricted to predominant class I and II alleles of human leukocyte antigens (HLA). These are similar to peptides of mycobacterial proteins and considerable numbers of them are promiscuous. Some of the identified antigens corroborated with established autoimmune diseases linked with mycobacterial infection.</p> <p>Conclusions</p> <p>The present study reveals many target proteins and their putative T cell epitopes that might have significant application in understanding the molecular basis of possible T cell autoimmune reactions during <it>M. tuberculosis </it>infections.</p
Crossover of the dimensionality of 3d spin fluctuations in LaCoPO
dc magnetization and 31^P spin lattice relaxation rate in the polycrystalline
sample of LaCoPO suggest a spin fluctuation dominated ferromagnetically ordered
state. Moreover, NMR data clearly indicate a crossover from 2D to 3D spin
fluctuations across T_C. In contrast to isotropic hyperfine field, H_hf at the
31^P site in LaFePO, H_hf is anisotropic in LaCoPO. The data of spin lattice
relaxation rate also exhibit anisotropic spin fluctuation. The anisotropy
vanishes near T_C
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