887 research outputs found
X-ray Spectral and Variability Properties of Low-Mass AGN
We study the X-ray properties of a sample of 14 optically-selected low-mass
AGN whose masses lie within the range 1E5 -2E6 M(solar) with XMM-Newton. Only
six of these low-mass AGN have previously been studied with sufficient quality
X-ray data, thus, we more than double the number of low-mass AGN observed by
XMM-Newton with the addition of our sample. We analyze their X-ray spectral
properties and variability and compare the results to their more massive
counterparts. The presence of a soft X-ray excess is detectable in all five
objects which were not background dominated at 2-3 keV. Combined with previous
studies, this gives a total of 8 low-mass AGN with a soft excess. The low-mass
AGN exhibit rapid, short-term variability (hundreds to thousands of seconds) as
well as long-term variability (months to years). There is a well-known
anti-correlation between black hole mass and variability amplitude (normalized
excess variance). Comparing our sample of low-mass AGN with this relation we
find that all of our sample lie below an extrapolation of the linear relation.
Such a flattening of the relation at low masses (below about 1E6 M(solar)) is
expected if the variability in all AGN follows the same shape power spectrum
with a break frequency that is dependent on mass. Finally, we also found two
objects that show significant absorption in their X-ray spectrum, indicative of
type 2 objects, although they are classified as type 1 AGN based on optical
spectra.Comment: 12 pages, 5 figures, 7 tables, accepted for publication in MNRA
Transport Coefficients of Gluon Plasma
Transport coefficients of gluon plasma are calculated for a SU(3) pure gauge
model by lattice QCD simulations on and
lattices. Simulations are carried out at a slightly above the deconfinement
transition temperature , where a new state of matter is currently being
pursued in RHIC experiments. Our results show that the ratio of the shear
viscosity to the entropy is less than one and the bulk viscosity is consistent
with zero in the region, .Comment: 10 pages, Late
Coupling Nonlinear Sigma-Matter to Yang-Mills Fields: Symmetry Breaking Patterns
We extend the traditional formulation of Gauge Field Theory by incorporating
the (non-Abelian) gauge group parameters (traditionally simple spectators) as
new dynamical (nonlinear-sigma-model-type) fields. These new fields interact
with the usual Yang-Mills fields through a generalized minimal coupling
prescription, which resembles the so-called Stueckelberg transformation, but
for the non-Abelian case. Here we study the case of internal gauge symmetry
groups, in particular, unitary groups U(N). We show how to couple standard
Yang-Mills Theory to Nonlinear-Sigma Models on cosets of U(N): complex
projective, Grassman and flag manifolds. These different couplings lead to
distinct (chiral) symmetry breaking patterns and \emph{Higgs-less}
mass-generating mechanisms for Yang-Mills fields.Comment: 11 pages. To appear in Journal of Nonlinear Mathematical Physic
Quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR Observations of the New X-Ray Clocked Burster 1RXS J180408.9-342058
We report the quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR observations showing spectral state transitions in the neutron star low-mass X-ray binary 1RXS J180408.9−342058 during its 2015 outburst. We present results of the analysis of high-quality broad energy band (0.8–200 keV) data in three different spectral states: high/soft, low/very-hard, and transitional state. The broadband spectra can be described in general as the sum of thermal Comptonization and reflection due to illumination of an optically thick accretion disk. During the high/soft state, blackbody emission is generated from the accretion disk and the surface of the neutron star. This emission, measured at a temperature of kT_(bb) ~ 1.2 keV, is then Comptonized by a thick corona with an electron temperature of ~2.5 keV. For the transitional and low/very-hard state, the spectra are successfully explained with emission from a double Comptonizing corona. The first component is described by thermal Comptonization of seed disk/neutron star photons (kT_(bb) ~ 1.2 keV) by a cold corona cloud with kT_e ~ 8–10 keV, while the second one originates from lower temperature blackbody photons (kT_(bb) ≤ 0.1 keV) Comptonized by a hot corona (kT_e ~ 35 keV). Finally, from NuSTAR observations, there is evidence that the source is a new clocked burster. The average time between two successive X-ray bursts corresponds to ~7.9 and ~4.0 ks when the persistent emission decreases by a factor of ~2, moving from a very hard to transitional state. The accretion rate (~4 x 10⁻⁹ M⊙ yr ⁻¹) and the decay time of the X-ray bursts longer than ~30 s suggest that the thermonuclear emission is due to mixed H/He burning triggered by thermally unstable He ignition
Tips for research recruitment: The views of sexual minority youth
Researchers often experience difficulties recruiting hard-to-reach populations. This is especially so for studies involving those who have been historically stigmatized, such as individuals who challenge heteronormative expectations or people who experience mental ill health. The authors aimed to obtain the views of sexual minority adolescents (n=25) about what encouraged their participation in a research project. The authors used a general inductive approach to analyze interview data. Feedback consisted of 2 main overarching themes: tips and suggestions for future research and appreciate participants’ motivation to get involved in research. Strategies for how recruitment can be optimized for studies involving sexual minority young people are discussed
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Clinical perspectives of emerging pathogens in bleeding disorders.
As a result of immunological and nucleic-acid screening of plasma donations for transfusion-transmissible viruses, and the incorporation of viral reduction processes during plasma fractionation, coagulation-factor concentrates (CFC) are now judged safe in terms of many known infectious agents, including hepatitis B and C viruses, HIV, and human T-cell lymphotropic virus. However, emerging pathogens could pose future threats, particularly those with blood-borne stages that are resistant to viral-inactivation steps in the manufacturing process, such as non-lipid-coated viruses. As outlined in this Review, better understanding of infectious diseases allows challenges from newly described agents of potential concern in the future to be anticipated, but the processes of zoonotic transmission and genetic selection or modification ensure that plasma-derived products will continue to be subject to infectious concerns. Manufacturers of plasma-derived CFC have addressed the issue of emerging infectious agents by developing recombinant products that limit the need for human plasma during production. Such recombinant products have extended the safety profile of their predecessors by ensuring that all reagents used for cell culture, purification steps, and stabilisation and storage buffers are completely independent of human plasma
A Persistent Disk Wind in GRS 1915+105 with NICER
The bright, erratic black hole X-ray binary GRS 1915+105 has long been a
target for studies of disk instabilities, radio/infrared jets, and accretion
disk winds, with implications that often apply to sources that do not exhibit
its exotic X-ray variability. With the launch of NICER, we have a new
opportunity to study the disk wind in GRS 1915+105 and its variability on short
and long timescales. Here we present our analysis of 39 NICER observations of
GRS 1915+105 collected during five months of the mission data validation and
verification phase, focusing on Fe XXV and Fe XXVI absorption. We report the
detection of strong Fe XXVI in 32 (>80%) of these observations, with another
four marginal detections; Fe XXV is less common, but both likely arise in the
well-known disk wind. We explore how the properties of this wind depends on
broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio,
and fractional RMS variability. The trends with count rate and RMS are
consistent with an average wind column density that is fairly steady between
observations but varies rapidly with the source on timescales of seconds. The
line dependence on spectral hardness echoes known behavior of disk winds in
outbursts of Galactic black holes; these results clearly indicate that NICER is
a powerful tool for studying black hole winds.Comment: Accepted for publication in ApJL. Comments welcom
Radiation Pressure Dominate Regime of Relativistic Ion Acceleration
The electromagnetic radiation pressure becomes dominant in the interaction of
the ultra-intense electromagnetic wave with a solid material, thus the wave
energy can be transformed efficiently into the energy of ions representing the
material and the high density ultra-short relativistic ion beam is generated.
This regime can be seen even with present-day technology, when an exawatt laser
will be built. As an application, we suggest the laser-driven heavy ion
collider.Comment: 10 pages, 4 figure
Revealing the spectral state transition of the Clocked Burster, GS 1826-238 with NuSTAR StrayCats
We present the long term analysis of GS 1826-238, a neutron star X-ray binary
known as the "Clocked Burster", using data from NuSTAR StrayCats. StrayCats, a
catalogue of NuSTAR stray light data, contains data from bright, off-axis X-ray
sources that have not been focused by the NuSTAR optics. We obtained stray
light observations of the source from 2014-2021, reduced and analyzed the data
using nustar-gen-utils Python tools, demonstrating the transition of source
from the "island" atoll state to a "banana" branch. We also present the
lightcurve analysis of Type I X-Ray bursts from the Clocked Burster and show
that the bursts from the banana/soft state are systematically shorter in
durations than those from the island/hard state and have a higher burst
fluence. From our analysis, we note an increase in mass accretion rate of the
source, and a decrease in burst frequency with the transition
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