5,644 research outputs found
Structure and Magnetic Fields in the Precessing Jet System SS 433 II. Intrinsic Brightness of the Jets
Deep Very Large Array imaging of the binary X-ray source SS 433, sometimes
classified as a microquasar, has been used to study the intrinsic brightness
distribution and evolution of its radio jets. The intrinsic brightness of the
jets as a function of age at emission of the jet material tau is recovered by
removal of the Doppler boosting and projection effects. We find that
intrinsically the two jets are remarkably similar when compared for equal tau,
and that they are best described by Doppler boosting of the form D^{2+alpha},
as expected for continuous jets. The intrinsic brightnesses of the jets as
functions of age behave in complex ways. In the age range 60 < tau < 150 days,
the jet decays are best represented by exponential functions of tau, but linear
or power law functions are not statistically excluded. This is followed by a
region out to tau ~ 250 days during which the intrinsic brightness is
essentially constant. At later times the jet decay can be fit roughly as
exponential or power law functions of tau.Comment: 30 Pages, 11 Figures, Submitted to Ap
Full-Stokes polarimetry with circularly polarized feeds - Sources with stable linear and circular polarization in the GHz regime
We present a pipeline that allows recovering reliable information for all
four Stokes parameters with high accuracy. Its novelty relies on the treatment
of the instrumental effects already prior to the computation of the Stokes
parameters contrary to conventional methods, such as the M\"uller matrix one.
The instrumental linear polarization is corrected across the whole telescope
beam and significant Stokes and can be recovered even when the recorded
signals are severely corrupted. The accuracy we reach in terms of polarization
degree is of the order of 0.1-0.2 %. The polarization angles are determined
with an accuracy of almost 1. The presented methodology was applied
to recover the linear and circular polarization of around 150 Active Galactic
Nuclei. The sources were monitored from July 2010 to April 2016 with the
Effelsberg 100-m telescope at 4.85 GHz and 8.35 GHz with a cadence of around
1.2 months. The polarized emission of the Moon was used to calibrate the
polarization angle. Our analysis showed a small system-induced rotation of
about 1 at both observing frequencies. Finally, we identify five
sources with significant and stable linear polarization; three sources remain
constantly linearly unpolarized over the period we examined; a total of 11
sources have stable circular polarization degree and four of
them with non-zero . We also identify eight sources that maintain
a stable polarization angle over the examined period. All this is provided to
the community for polarization observations reference. We finally show that our
analysis method is conceptually different from the traditionally used ones and
performs better than the M\"uller matrix method. Although it was developed for
a system equipped with circularly polarized feeds it can easily be modified for
systems with linearly polarized feeds as well.Comment: 19 pages, 17 figures, accepted for publication in Astronomy &
Astrophysics on May 30, 201
Health and lifestyle of Nepalese migrants in the UK
Background: The health status and lifestyle of migrants is often poorer than that of the general
population of their host countries. The Nepalese represent a relatively small, but growing,
immigrant community in the UK, about whom very little is known in term of public health.
Therefore, our study examined the health and lifestyle of Nepalese migrants in the UK.
Methods: A cross-sectional survey of Nepalese migrants in UK was conducted in early 2007 using
a postal, self-administered questionnaire in England and Scotland (n = 312), and telephone
interviews in Wales (n = 15). The total response rate was 68% (327 out of 480). Data were analyzed
to establish whether there are associations between socio-economic and lifestyle factors. A
multivariate binary logistic regression was applied to find out independent effect of personal factors
on health status.
Results: The majority of respondents was male (75%), aged between 30 and 45 (66%), married or
had a civil partner (83%), had university education (47%) and an annual family income (69%) ranging
from £5,035 to £33,300. More than one third (39%) of the respondents have lived in the UK for 1
to 5 years and approximately half (46%) were longer-term residents. Most (95%) were registered
with a family doctor, but only 38% with a dentist. A low proportion (14%) of respondents smoked
but more than half (61%) consumed alcohol. More than half (57%) did not do regular exercises and
nearly one fourth (23%) of respondents rated their health as poor. Self reported 'good' health
status of the respondents was independently associated with immigration status and doing regular exercise
Conclusion: The self reported health status and lifestyle, health seeking behaviour of Nepalese
people who are residing in UK appears to be good. However, the overall regular exercise and dentist registration was rather poor. Health promotion, especially aimed at Nepalese migrants could help encourage them to exercise regularly and assist them to register with a dentist
A relativistic model of the radio jets in NGC 315
We apply our intrinsically symmetrical, decelerating relativistic jet model
to deep VLA imaging of the inner 140 arcsec of the giant low-luminosity radio
galaxy NGC 315. An optimized model accurately fits the data in both total
intensity and linear polarization. We infer that the velocity, emissivity and
field structure in NGC 315 are very similar to those of the other
low-luminosity sources we have modelled, but that all of the physical scales
are larger by a factor of about 5. We derive an inclination to the line of
sight of 38 degrees for the jets. Where they first brighten, their on-axis
velocity is approximately v/c = 0.9. They decelerate to v/c = 0.4 between 8 and
18 kpc from the nucleus and the velocity thereafter remains constant. The speed
at the edge of the jet is roughly 0.6 of the on-axis value where it is best
constrained, but the transverse velocity profile may deviate systematically
from the Gaussian form we assume. The proper emissivity profile is split into
three power-law regions separated by shorter transition zones. In the first of
these, at 3 kpc (the flaring point) the jets expand rapidly at constant
emissivity, leading to a large increase in the observed brightness on the
approaching side. At 10 kpc, the emissivity drops abruptly by a factor of 2.
Where the jets are well resolved their rest-frame emission is
centre-brightened. The magnetic field is modelled as random on small scales but
anisotropic and we rule out a globally ordered helical configuration. To a
first approximation, the field evolves from a mixture of longitudinal and
toroidal components to predominantly toroidal, but it also shows variations in
structure along and across the jets, with a significant radial component in
places. Simple adiabatic models fail to fit the emissivity variations.Comment: 20 pages, 17 figures, MNRAS (in press
Coexisting conical bipolar and equatorial outflows from a high-mass protostar
The BN/KL region in the Orion molecular cloud is an archetype in the study of
the formation of stars much more massive than the Sun. This region contains
luminous young stars and protostars, but it is difficult to study because of
overlying dust and gas. Our basic expectations are shaped to some extent by the
present theoretical picture of star formation, the cornerstone of which is that
protostars acrete gas from rotating equatorial disks, and shed angular momentum
by ejecting gas in bipolar outflows. The main source of the outflow in the
BN/KL region may be an object known as radio source I, which is commonly
believed to be surrounded by a rotating disk of molecular material. Here we
report high-resolution observations of silicon monoxide (SiO) and water maser
emission from the gas surrounding source I; we show that within 60 AU (about
the size of the Solar System), the region is dominated by a conical bipolar
outflow, rather than the expected disk. A slower outflow, close to the
equatorial plane of the protostellar system, extends to radii of 1,000 AU.Comment: 10 pages, 2 figures. Accepted by Nature. To appear December 199
Gray platelet syndrome: proinflammatory megakaryocytes and α-granule loss cause myelofibrosis and confer metastasis resistance in mice.
NBEAL2 encodes a multidomain scaffolding protein with a putative role in granule ontogeny in human platelets. Mutations in NBEAL2 underlie gray platelet syndrome (GPS), a rare inherited bleeding disorder characterized by a lack of α-granules within blood platelets and progressive bone marrow fibrosis. We present here a novel Nbeal2(-/-) murine model of GPS and demonstrate that the lack of α-granules is due to their loss from platelets/mature megakaryocytes (MKs), and not by initial impaired formation. We show that the lack of Nbeal2 confers a proinflammatory phenotype to the bone marrow MKs, which in combination with the loss of proteins from α-granules drives the development of bone marrow fibrosis. In addition, we demonstrate that α-granule deficiency impairs platelet function beyond their purely hemostatic role and that Nbeal2 deficiency has a protective effect against cancer metastasis.This work was funded by the British Heart
Foundation to CG (FS09/039) and WHO and AR (RG/09/12/28096); NHSBT to CB and HM;
Wellcome Trust (WT098051) to ZM, ELC, JE, HWJ and AOS.This is the accepted manuscript. The final published version is available from Blood at http://www.bloodjournal.org/content/early/2014/09/25/blood-2014-04-566760
Diffuse steep-spectrum sources from the 74 MHz VLSS survey
Galaxy clusters grow by a sequence of mergers with other clusters and galaxy
groups. During these mergers, shocks and/or turbulence are created within the
intracluster medium (ICM). In this process, particles could be accelerated to
highly relativistic energies. The synchrotron radiation from these particles is
observed in the form of radio relics and halos that are generally characterized
by a steep radio spectral index. Shocks can also revive fossil radio plasma
from a previous episode of AGN activity, creating a so-called radio phoenix.
Here we present multi-frequency radio observations of diffuse steep-spectrum
radio sources selected from the 74 MHz VLSS survey. Previous GMRT observations
showed that some of these sources had filamentary and elongated morphologies,
which are expected for radio relics.
We carried out radio continuum observations at 325 MHz with the GMRT.
Observations with the VLA and WSRT were taken at 1.4 GHz in full polarization
mode. Optical images around the radio sources were taken with the WHT and INT
telescopes. Most of the sources in our sample consist of old radio plasma from
AGNs located in small galaxy clusters. The sources can be classified as AGN
relics or radio phoenices. The spectral indices across most of the radio
sources display large variations. We conclude that diffuse steep-spectrum radio
sources are not only found in massive X-ray luminous galaxy clusters but also
in smaller systems. Future low-frequency surveys will uncover large numbers of
steep-spectrum radio relics related to previous episodes of AGN activity.
[abridged]Comment: 15 pages, 15 figures, accepted for publication in A&A on December 9,
201
Circular Polarization of Radio Emission from Relativistic Jets
In inhomogeneous optically thick synchrotron sources a substantial part of
the electron population at low energies can be hidden by self-absorption and
overpowered by high energy electrons in optically thin emission. These
invisible electrons produce Faraday rotation and conversion, leaving their
footprints in the linear and circular polarized radiation of the source. An
important factor is also the magnetic field structure, which can be
characterized in most cases by a global magnetic field and a turbulent
component. We present the basic radiative transfer coefficients for polarized
synchrotron radiation and apply them to the standard jet model for relativistic
radio jets. The model can successfully explain the unusual circular and linear
polarization of the Galactic Centre radio source Sgr A* and its sibling M81*.
It also can account for the circular polarization found in jets of more
luminous quasars and X-ray binaries. The high ratio of circular to linear
polarization requires the presence of a significant fraction of hidden matter
and low-energy electrons in these jets. The stable handedness of circular
polarization requires stable global magnetic field components with
non-vanishing magnetic flux along the jet, while the low degree of total
polarization implies also a significant turbulent field. The most favoured
magnetic field configuration is that of a helix, while a purely toroidal field
is unable to produce significant circular polarization. If connected to the
magnetosphere of the black hole, the circular polarization and the jet
direction determine the magnetic poles of the system which is stable over long
periods of time. This may also have implications for possible magnetic field
configurations in accretion flows.Comment: A&A, submitted, LaTex, 13 pages, 7 figures, 2 animations (not
included, see webpage), also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#cpthe
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