53 research outputs found
A large-scale survey of X-ray filaments in the Galactic Centre
We present a catalogue of 17 filamentary X-ray features located within a
68\times34 arcmin^2 view centred on the Galactic Centre region from images
taken by Chandra. These features are described by their morphological and
spectral properties. Many of the X-ray features have non-thermal spectra that
are well fitted by an absorbed power law. Of the 17 features, we find six that
have not been previously detected, four of which are outside the immediate
20\times20 arcmin^2 area centred on the Galactic Centre. Seven of the 17
identified filaments have morphological and spectral properties expected for
pulsar wind nebulae (PWNe) with X-ray luminosities of 5\times10^32 to 10^34 erg
s^-1 in the 2.0-10.0 keV band and photon indices in the range of \Gamma = 1.1
to 1.9. In one feature, we suggest the strong neutral Fe K\alpha emission line
to be a possible indicator for past activity of Sgr A*. For G359.942-0.03, a
particular filament of interest, we propose the model of a ram pressure
confined stellar wind bubble from a massive star to account for the morphology,
spectral shape and 6.7 keV He-like Fe emission detected. We also present a
piecewise spectral analysis on two features of interest, G0.13-0.11 and
G359.89-0.08, to further examine their physical interpretations. This analysis
favours the PWN scenario for these features.Comment: 12 pages, 10 figure
Sagittarius A* Accretion Flow and Black Hole Parameters from General Relativistic Dynamical and Polarized Radiative Modeling
We obtain estimates of Sgr A* accretion flow and black hole parameters by
fitting polarized sub-mm observations with spectra computed using
three-dimensional (3D) general relativistic (GR) magnetohydrodynamical (MHD)
(GRMHD) simulations. Observations are compiled from averages over many epochs
from reports in 29 papers for estimating the mean fluxes Fnu, linear
polarization (LP) fractions, circular polarization (CP) fractions, and electric
vector position angles (EVPAs). GRMHD simulations are computed with
dimensionless spins a_*=0,0.5,0.7,0.9,0.98 over a 20,000M time interval. We
perform fully self-consistent GR polarized radiative transfer using our new
code to explore the effects of spin a_*, inclination angle \theta, position
angle (PA), accretion rate Mdot, and electron temperature Te (Te is reported
for radius 6M). By fitting the mean sub-mm fluxes and LP/CP fractions, we
obtain estimates for these model parameters and determine the physical effects
that could produce polarization signatures. Our best bet model has a_*=0.5,
\theta=75deg, PA=115deg, Mdot=4.6*10^{-8}M_Sun/year, and Te=3.1*10^10K at 6M.
The sub-mm CP is mainly produced by Faraday conversion as modified by Faraday
rotation, and the emission region size at 230GHz is consistent with the VLBI
size of 37microas. Across all spins, model parameters are in the ranges
\theta=42deg-75deg, Mdot=(1.4-7.0)*10^{-8}M_Sun/year, and Te=(3-4)*10^10K.
Polarization is found both to help differentiate models and to introduce new
observational constraints on the effects of the magnetic field that might not
be fit by accretion models so-far considered.Comment: 19 pages, 11 figures, accepted to Ap
Winds from clu\sters with non-uniform stellar distributions
We present analytic and numerical models of the `cluster wind' resulting from
the multiple interactions of the winds ejected by the stars of a dense cluster
of massive stars. We consider the case in which the distribution of stars
(i.e., the number of stars per unit volume) within the cluster is spherically
symmetric, has a power-law radial dependence, and drops discontinuously to zero
at the outer radius of the cluster. We carry out comparisons between an
analytic model (in which the stars are considered in terms of a spatially
continuous injection of mass and energy) and 3D gasdynamic simulations (in
which we include 100 stars with identical winds, located in 3D space by
statistically sampling the stellar distribution function). From the analytic
model, we find that for stellar distributions with steep enough radial
dependencies the cluster wind flow develops a very high central density and a
non-zero central velocity, and for steeper dependencies it becomes fully
supersonic throughout the volume of the cluster (these properties are partially
reproduced by the 3D numerical simulations). Therefore, the wind solutions
obtained for stratified clusters can differ dramatically from the case of a
homogeneous stellar distribution (which produces a cluster wind with zero
central velocity, and a fully subsonic flow within the cluster radius).
Finally, from our numerical simulations we compute predictions of X-ray
emission maps and luminosities, which can be directly compared with
observations of cluster wind flows.Comment: 10 pages, 11 figures. MNRAS - Accepted 2007 June 29. Received 2007
June 28; in original form 2007 May 2
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Milestones in the Observations of Cosmic Magnetic Fields
Magnetic fields are observed everywhere in the universe. In this review, we
concentrate on the observational aspects of the magnetic fields of Galactic and
extragalactic objects. Readers can follow the milestones in the observations of
cosmic magnetic fields obtained from the most important tracers of magnetic
fields, namely, the star-light polarization, the Zeeman effect, the rotation
measures (RMs, hereafter) of extragalactic radio sources, the pulsar RMs, radio
polarization observations, as well as the newly implemented sub-mm and mm
polarization capabilities.
(Another long paragraph is omitted due to the limited space here)Comment: Invited Review (ChJA&A); 32 pages. Sorry if your significant
contributions in this area were not mentioned. Published pdf & ps files (with
high quality figures) now availble at http://www.chjaa.org/2002_2_4.ht
The Role of Phytonutrients in Skin Health
Photodamage is known to occur in skin with exposure to sunlight, specifically ultraviolet (UV) radiation. Such damage includes inflammation, oxidative stress, breakdown of the extracellular matrix, and development of cancer in the skin. Sun exposure is considered to be one of the most important risk factors for both nonmelanoma and melanoma skin cancers. Many phytonutrients have shown promise as photoprotectants in clinical, animal and cell culture studies. In part, the actions of these phytonutrients are thought to be through their actions as antioxidants. In regard to skin health, phytonutrients of interest include vitamin E, certain flavonoids, and the carotenoids, β-carotene, lycopene and lutein
Detection of bipolar flow associated with UX Ori: an intermediate-mass pre-main sequence star
Detection of bipolar flow associated with UX Ori: an intermediate-mass pre-main sequence star
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