366 research outputs found
IKT 16: the first X-ray confirmed composite SNR in the SMC
Aims: IKT 16 is an X-ray and radio-faint supernova remnant (SNR) in the Small
Magellanic Cloud (SMC). A detailed X-ray study of this SNR with XMM-Newton
confirmed the presence of a hard X-ray source near its centre, indicating the
detection of the first composite SNR in the SMC. With a dedicated Chandra
observation we aim to resolve the point source and confirm its nature. We also
acquire new ATCA observations of the source at 2.1 GHz with improved flux
density estimates and resolution.
Methods: We perform detailed spatial and spectral analysis of the source.
With the highest resolution X-ray and radio image of the centre of the SNR
available today, we resolve the source and confirm its pulsar wind nebula (PWN)
nature. Further, we constrain the geometrical parameters of the PWN and perform
spectral analysis for the point source and the PWN separately. We also test for
the radial variations of the PWN spectrum and its possible east west asymmetry.
Results: The X-ray source at the centre of IKT 16 can be resolved into a
symmetrical elongated feature centering a point source, the putative pulsar.
Spatial modeling indicates an extent of 5.2 arcsec of the feature with its axis
inclined at 82 degree east from north, aligned with a larger radio feature
consisting of two lobes almost symmetrical about the X-ray source. The picture
is consistent with a PWN which has not yet collided with the reverse shock. The
point source is about three times brighter than the PWN and has a hard spectrum
of spectral index 1.1 compared to a value 2.2 for the PWN. This points to the
presence of a pulsar dominated by non-thermal emission. The expected E_{dot} is
~ 10^37 erg s^-1 and spin period < 100 ms. However, the presence of a compact
nebula unresolved by Chandra at the distance of the SMC cannot completely be
ruled out.Comment: 9 pages, 6 figures, 2 tables, Accepted for publication in Astronomy &
Astrophysic
A fresh perspective on the 3-D dynamics of Tycho's supernova remnant: ejecta asymmetries in X-rays
450 years after the explosion of the Type Ia SN1572, the dynamics of the
Tycho supernova remnant can give us keys to understand the explosion mechanism
and the interaction of the remnant with the interstellar medium. To probe the
asymmetries and the evolution of the SNR, we track the ejecta dynamics using
new methods applied to the deep X-ray observations available in the Chandra
space telescope archive. For the line of sight velocity measurement Vz, we use
the Doppler effect focused on the bright Si line in the 1.6-2.1 keV band. Using
the component separation tool General Morphological Component Analysis (GMCA),
we successfully disentangle the red and blueshifted Si ejecta emission. This
allows us to reconstruct a map of the peak energy of the Si line with a total
coverage of the SNR at a 2'' resolution and a proxy of the velocity in the line
of sight. For the proper motions in the plane of the sky Vxy, we develop a new
method, named Poisson Optical Flow, to measure the displacement of 2D features
between the observations of 2003 and 2009. The result is a field of 1700
velocity vectors covering the entire SNR. These exhaustive 3D velocity
measurements reveal the complex and patchy dynamics of the SNR. At the
large-scale, an asymmetry with the North being dominantly blueshifted and the
South redshifted is observed. The proper motion vector field Vxy highlights
different dynamics between the East and the West parts of the SNR. The eastern
velocity field is more disturbed by external inhomogeneities and the South-East
ejecta knot. In particular, a slow-down is observed in the North-East which
could be due to the interaction with higher densities as seen in other
wavelengths. The vector field is also used to backtrace the center of the
explosion which is then compared with potential stellar progenitors distances
from the latest Gaia DR3, leaving only stars B and E as possible candidates.Comment: Accepted for publication in A&A. 18 pages, 12 figure
The warm interstellar medium around the Cygnus Loop
Observations of the oxygen lines [OII]3729 and [OIII]5007 in the medium
immediately beyond the Cygnus Loop supernova remnant were carried out with the
scanning Fabry-P\'erot spectrophotometer ESOP. Both lines were detected in
three different directions - east, northeast and southwest - and up to a
distance of 15 pc from the shock front. The ionized medium is in the immediate
vicinity of the remnant, as evinced by the smooth brightening of both lines as
the adiabatic shock transition (defined by the X-ray perimeter) is crossed.
These lines are usually brighter around the Cygnus Loop than in the general
background in directions where the galactic latitude is above 5 degrees. There
is also marginal (but significant) evidence that the degree of ionization is
somewhat larger around the Cygnus Loop. We conclude that the energy necessary
to ionize this large bubble of gas could have been supplied by an O8 or O9 type
progenitor or the particles heated by the expanding shock front. The second
possibility, though highly atractive, would have to be assessed by extensive
modelling.Comment: 18 pages, 8 figures, ApJ 512 in pres
Comprehensive in vitro Proarrhythmia Assay (CiPA): Pending issues for successful validation and implementation
International audienceIntroduction: The Comprehensive in vitro Proarrhythmia Assay (CiPA) is a nonclinical Safety Pharmacology paradigm for discovering electrophysiological mechanisms that are likely to confer proarrhythmic liability to drug candidates intended for human use.Topics covered: Key talks delivered at the âCiPA on my mindâ session, held during the 2015 Annual Meeting of the Safety Pharmacology Society (SPS), are summarized. Issues and potential solutions relating to crucial constituents [e.g., biological materials (ion channels and pluripotent stem cell-derived cardiomyocytes), study platforms, drug solutions, and data analysis] of CiPA core assays are critically examined.Discussion: In order to advance the CiPA paradigm from the current testing and validation stages to a research and regulatory drug development strategy, systematic guidance by CiPA stakeholders is necessary to expedite solutions to pending and newly arising issues. Once a study protocol is proved to yield robust and reproducible results within and across laboratories, it can be implemented as qualified regulatory procedure
Elliptic periods for finite fields
We construct two new families of basis for finite field extensions. Basis in
the first family, the so-called elliptic basis, are not quite normal basis, but
they allow very fast Frobenius exponentiation while preserving sparse
multiplication formulas. Basis in the second family, the so-called normal
elliptic basis are normal basis and allow fast (quasi linear) arithmetic. We
prove that all extensions admit models of this kind
Archaebiotics: Archaea as Pharmabiotics for Treating Chronic Disease in Humans?
Recent findings highlight the role of the human gut microbiota in various disorders. For example, atherosclerosis frequently seems to be the consequence of gut microbiotaâderived metabolism of some dietary components. Pharmabiotics (i.e., live/dead microbes and microbe-derived substances) and probiotics (live microorganisms with a health benefit when administered in adequate amounts) are a means to counteract these deleterious effects. Among the latter, microbes now being used or, being currently developed, are bacteria and eukaryotes (yeasts), so omitting the third domain of lifeâthe archaea, despite their unique properties that could be of great interest to human health. Here, we promote the idea that some specific archaea are potential next-generation probiotics. This is based on an innovative example of the bioremediation of a gut microbial metabolite. Indeed, besides the fact that they are archaea (i.e. originating from a domain of life from which no pathogens of humans/animals/plants are currently known), they are rationally selected based on (i) being naturally human-hosted, (ii) having a unique metabolism not performed by other human gut microbes, (iii) depleting a deleterious atherogenic compound generated by the human gut microbiota and (iv) generating a health inert gas
The blast wave of Tycho's supernova remnant
We use the Chandra X-ray Observatory to study the region in the Tycho
supernova remnant between the blast wave and the shocked ejecta interface or
contact discontinuity. This zone contains all the history of the shock-heated
gas and cosmic-ray acceleration in the remnant. We present for the first time
evidence for significant spatial variations of the X-ray synchrotron emission
in the form of spectral steepening from a photon index of 2.6 right at the
blast wave to a value of 3.0 several arcseconds behind. We interpret this
result along with the profiles of radio and X-ray intensity using a
self-similar hydrodynamical model including cosmic ray backreaction that
accounts for the observed ratio of radii between the blast wave and contact
discontinuity. Two different assumptions were made about the post-shock
magnetic field evolution: one where the magnetic field (amplified at the shock)
is simply carried by the plasma flow and remains relatively high in the
post-shock region [synchrotron losses limited rim case], and another where the
amplified magnetic field is rapidly damped behind the blast wave [magnetic
damping case]. Both cases fairly well describe the X-ray data, however both
fail to explain the observed radio profile. The projected synchrotron emission
leaves little room for the presence of thermal emission from the shocked
ambient medium. This can only be explained if the pre-shock ambient medium
density in the vicinity of the Tycho supernova remnant is below 0.6 cm-3.Comment: Accepted for publication in ApJ - 61 pages, 17 figure
- âŠ