2,428 research outputs found
Broadband observations of the X-ray burster 4U 1705-44 with BeppoSAX
4U 1705-44 is one of the most-studied type I X-ray burster and Atoll sources.
This source represents a perfect candidate to test different models proposed to
self-consistently track the physical changes occurring between different
spectral states because it shows clear spectral state transitions. The
broadband coverage, the sensitivity and energy resolution of the BeppoSAX
satellite offers the opportunity to disentangle the components that form the
total X-ray spectrum and to study their changes according to the spectral
state. Using two BeppoSAX observations carried out in August and October 2000,
respectively, for a total effective exposure time of about 100 ks, we study the
spectral evolution of the source from a soft to hard state. Energy spectra are
selected according to the source position in the color-color diagram (CCD)
Results. We succeeded in modeling the spectra of the source using a physical
self-consistent scenario for both the island and banana branches (the double
Comptonization scenario). The components observed are the soft Comptonization
and hard Comptonization, the blackbody, and a reflection component with a broad
iron line. When the source moves from the banana state to the island state, the
parameters of the two Comptonization components change significantly and the
blackbody component becomes too weak to be detected. We interpret the soft
Comptonization component as emission from the hot plasma surrounding the
neutron star, hard Comptonization as emission from the disk region, and the
blackbody component as emission from the inner accretion disk. The broad
feature in the iron line region is compatible with reflection from the inner
accretion disk.Comment: 8 pages, 10 figures, accepted for publication by A&
Disentangling the jet emission from protostellar systems. The ALMA view of VLA1623
Context: High-resolution studies of class 0 protostars represent the key to
constraining protostar formation models. VLA16234-2417 represents the prototype
of class 0 protostars, and it has been recently identified as a triple
non-coeval system. Aim: We aim at deriving the physical properties of the jets
in VLA16234-2417 using tracers of shocked gas. Methods: ALMA Cycle 0 Early
Science observations of CO(2-1) in the extended configuration are presented in
comparison with previous SMA CO(3-2) and Herschel-PACS [OI}] 63 micron
observations. Gas morphology and kinematics were analysed to constrain the
physical structure and origin of the protostellar outflows. Results: We reveal
a collimated jet component associated with the [OI] 63 micron emission at about
8'' (about 960 AU) from source B. This newly detected jet component is
inversely oriented with respect to the large-scale outflow driven by source A,
and it is aligned with compact and fast jet emission very close to source B
(about 0.3'') rather than with the direction perpendicular to the A disk. We
also detect a cavity-like structure at low projected velocities, which
surrounds the [OI] 63 micron emission and is possibly associated with the
outflow driven by source A. Finally, no compact outflow emission is associated
with source W. Conclusions: Our high-resolution ALMA observations seem to
suggest there is a fast and collimated jet component associated with source B.
This scenario would confirm that source B is younger than A, that it is in a
very early stage of evolution, and that it drives a faster, more collimated,
and more compact jet with respect to the large-scale slower outflow driven by
A. However, a different scenario of a precessing jet driven by A cannot be
firmly excluded from the present observations.Comment: Accepted for publication in Astronomy & Astrophysic
Observing Ultra High Energy Cosmic Particles from Space: SEUSO, the Super Extreme Universe Space Observatory Mission
The experimental search for ultra high energy cosmic messengers, from eV to beyond eV, at the very end of the known energy
spectrum, constitutes an extraordinary opportunity to explore a largely unknown
aspect of our universe. Key scientific goals are the identification of the
sources of ultra high energy particles, the measurement of their spectra and
the study of galactic and local intergalactic magnetic fields. Ultra high
energy particles might, also, carry evidence of unknown physics or of exotic
particles relics of the early universe. To meet this challenge a significant
increase in the integrated exposure is required. This implies a new class of
experiments with larger acceptances and good understanding of the systematic
uncertainties. Space based observatories can reach the instantaneous aperture
and the integrated exposure necessary to systematically explore the ultra high
energy universe. In this paper, after briefly summarising the science case of
the mission, we describe the scientific goals and requirements of the SEUSO
concept. We then introduce the SEUSO observational approach and describe the
main instrument and mission features. We conclude discussing the expected
performance of the mission
A relativistic iron emission line from the neutron star low-mass X-ray binary GX 3+1
We present the results of a spectroscopic study of the Fe K{\alpha} emission
of the persistent neutron-star atoll low-mass X-ray binary and type I X-ray
burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux
modulation over several years and we observed it during its fainter phase,
which corresponds to an X-ray luminosity of Lx~10^37 ergs/s. When fitted with a
two-component model, the X-ray spectrum shows broad residuals at \sim6-7 keV
that can be ascribed to an iron K{\alpha} fluorescence line. In addition, lower
energy features are observed at \sim3.3 keV, \sim3.9 keV and might originate
from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a
relativistically smeared profile. This result is robust against possible
systematics caused by instrumental pile-up effects. Assuming that the line is
produced by reflection from the inner accretion disk, we infer an inner disk
radius of \sim25 Rg and a disk inclination of 35{\deg} < i < 44{\deg}.Comment: 4 pages, 3 figures Accepted for publication in Astronomy and
Astrophysic
Casimir interaction of two plates inside a cylinder
The new exact formulas for the attractive Casimir force acting on each of the
two identical perfectly conducting plates moving freely inside an infinite
perfectly conducting cylinder with the same cross section are derived at zero
and finite temperatures by making use of the zeta function technique. The long
and short distance behaviour of the plates' free energy is investigated.Comment: 14 pages, 1 figure, latex2
A smooth cascade of wrinkles at the edge of a floating elastic film
The mechanism by which a patterned state accommodates the breaking of
translational symmetry by a phase boundary or a sample wall has been addressed
in the context of Landau branching in type-I superconductors, refinement of
magnetic domains, and compressed elastic sheets. We explore this issue by
studying an ultrathin polymer sheet floating on the surface of a fluid,
decorated with a pattern of parallel wrinkles. At the edge of the sheet, this
corrugated profile meets the fluid meniscus. Rather than branching of wrinkles
into generations of ever-smaller sharp folds, we discover a smooth cascade in
which the coarse pattern in the bulk is matched to fine structure at the edge
by the continuous introduction of discrete, higher wavenumber Fourier modes.
The observed multiscale morphology is controlled by a dimensionless parameter
that quantifies the relative strength of the edge forces and the rigidity of
the bulk pattern.Comment: 4 pages, 4 figure
Herschel PACS observations of shocked gas associated with the jets of L1448 and L1157
In the framework of the WISH key program, several H2O (E_u>190 K), high-J CO,
[OI], and OH transitions are mapped with PACS in two shock positions along the
two prototypical low-luminosity outflows L1448 and L1157. Previous HIFI H2O
observations (E_u=53-249 K) and complementary Spitzer mid-IR H2 data are also
used, with the aim of deriving a complete picture of the excitation conditions.
At all selected spots a close spatial association between H2O, mid-IR H2, and
high-J CO emission is found, whereas the low-J CO emission traces either
entrained ambient gas or a remnant of an older shock. The excitation analysis
at L1448-B2 suggests that a two-component model is needed to reproduce the H2O,
CO, and mid-IR H2 lines: an extended warm component (T~450 K) is traced by the
H2O emission with E_u =53-137 K and by the CO lines up to J=22-21, and a
compact hot component (T=1100 K) is traced by the H2O emission with E_u>190 K
and by the higher-J CO lines. At L1448-B2 we obtain an H2O abundance
(3-4)x10^{-6} for the warm component and (0.3-1.3)x10^{-5} for the hot
component; we also detect OH and blue-shifted [OI] emission, spatially
coincident with the other molecular lines and with [FeII] emission. This
suggests a dissociative shock for these species, related to the embedded atomic
jet. On the other hand, a non-dissociative shock at the point of impact of the
jet on the cloud is responsible for the H2O and CO emission. The other examined
shock positions show an H2O excitation similar to L1448-B2, but a slightly
higher H2O abundance (a factor of 4). The two gas components may represent a
gas stratification in the post-shock region. The extended and low-abundance
warm component traces the post-shocked gas that has already cooled down to a
few hundred Kelvin, whereas the compact and possibly higher-abundance hot
component is associated with the gas that is currently undergoing a shock
episode.Comment: Accepted for publication in Astronomy and Astrophysic
A QTL genome scan of the metabolic syndrome and its component traits
BACKGROUND: Because high blood pressure, altered lipid levels, obesity, and diabetes so frequently occur together, they are sometimes collectively referred to as the metabolic syndrome. While there have been many studies of each metabolic syndrome trait separately, few studies have attempted to analyze them combined, i.e., as one composite variable, in quantitative trait linkage or association analysis. We used genotype and phenotype data from the Framingham Heart Study to perform a full-genome scan for quantitative trait loci underlying the metabolic syndrome. RESULTS: Heritability estimates for all of the covariate-adjusted and age- and gender-standardized individual traits, and the composite metabolic syndrome trait, were all fairly high (0.39–0.62), and the composite trait was among the highest at 0.61. The composite trait yielded no regions with suggestive linkage by Lander and Kruglyak's criteria, although there were several noteworthy regions for individual traits, some of which were also observed for the composite variable. CONCLUSION: Despite its high heritability, the composite metabolic syndrome trait variable did not increase the power to detect or localize linkage peaks in this sample. However, this strategy and related methods of combining correlated individual traits deserve further investigation, particularly in settings with complex causal pathways
Resolving the shocked gas in HH54 with Herschel: CO line mapping at high spatial and spectral resolution
The HH54 shock is a Herbig-Haro object, located in the nearby Chamaeleon II
cloud. Observed CO line profiles are due to a complex distribution in density,
temperature, velocity, and geometry. Resolving the HH54 shock wave in the
far-infrared cooling lines of CO constrain the kinematics, morphology, and
physical conditions of the shocked region. We used the PACS and SPIRE
instruments on board the Herschel space observatory to map the full FIR
spectrum in a region covering the HH54 shock wave. Complementary Herschel-HIFI,
APEX, and Spitzer data are used in the analysis as well. The observed features
in the line profiles are reproduced using a 3D radiative transfer model of a
bow-shock, constructed with the Line Modeling Engine code (LIME). The FIR
emission is confined to the HH54 region and a coherent displacement of the
location of the emission maximum of CO with increasing J is observed. The peak
positions of the high-J CO lines are shifted upstream from the lower J CO lines
and coincide with the position of the spectral feature identified previously in
CO(10-9) profiles with HIFI. This indicates a hotter molecular component in the
upstream gas with distinct dynamics. The coherent displacement with increasing
J for CO is consistent with a scenario where IRAS12500-7658 is the exciting
source of the flow, and the 180 K bow-shock is accompanied by a hot (800 K)
molecular component located upstream from the apex of the shock and blueshifted
by -7 km s. The spatial proximity of this knot to the peaks of the
atomic fine-structure emission lines observed with Spitzer and PACS ([OI]63,
145 m) suggests that it may be associated with the dissociative shock as
the jet impacts slower moving gas in the HH54 bow-shock.Comment: 6 pages, 5 figure
[OI]63micron jets in class 0 sources detected by Herschel
We present Herschel PACS mapping observations of the [OI]63 micron line
towards protostellar outflows in the L1448, NGC1333-IRAS4, HH46, BHR71 and
VLA1623 star forming regions. We detect emission spatially resolved along the
outflow direction, which can be associated with a low excitation atomic jet. In
the L1448-C, HH46 IRS and BHR71 IRS1 outflows this emission is kinematically
resolved into blue- and red-shifted jet lobes, having radial velocities up to
200 km/s. In the L1448-C atomic jet the velocity increases with the distance
from the protostar, similarly to what observed in the SiO jet associated with
this source. This suggests that [OI] and molecular gas are kinematically
connected and that this latter could represent the colder cocoon of a jet at
higher excitation. Mass flux rates (\.M(OI)) have been measured from
the [OI]63micron luminosity adopting two independent methods. We find values in
the range 1-4 10 Mo/yr for all sources but HH46, for which an order of
magnitude higher value is estimated. \.M(OI) are compared with mass
accretion rates (\.M) onto the protostar and with \.M derived
from ground-based CO observations. \.M(OI)/\.M ratios are in
the range 0.05-0.5, similar to the values for more evolved sources.
\.M(OI) in HH46 IRS and IRAS4A are comparable to \.M(CO), while
those of the remaining sources are significantly lower than the corresponding
\.M(CO). We speculate that for these three sources most of the mass
flux is carried out by a molecular jet, while the warm atomic gas does not
significantly contribute to the dynamics of the system.Comment: 37 pages and 12 figures, accepted for publication on Astrophysical
Journa
- …