1,159 research outputs found
The origin of the 6.4 keV line emission and H ionization in the diffuse molecular gas of the Galactic center region
We investigate the origin of the diffuse 6.4 keV line emission recently
detected by Suzaku and the source of H_2ionization in the diffuse molecular gas
of the Galactic Center (GC) region. We show that Fe atoms and H_2 molecules in
the diffuse interstellar medium of the GC are not ionized by the same
particles. The Fe atoms are most likely ionized by X-ray photons emitted by Sgr
A* during a previous period of flaring activity of the supermassive black hole.
The measured longitudinal intensity distribution of the diffuse 6.4 keV line
emission is best explained if the past activity of Sgr A$* lasted at least
several hundred years and released a mean 2-100 keV luminosity > 10^38} erg
s^{-1}. The H_2 molecules of the diffuse gas can not be ionized by photons from
Sgr A*, because soft photons are strongly absorbed in the interstellar gas
around the central black hole. The molecular hydrogen in the GC region is most
likely ionized by low-energy cosmic rays, probably protons rather than
electrons, whose contribution into the diffuse 6.4 keV line emission is
negligible.Comment: 5 pages, 4 figues, accepted for publication in the Astrophysical
Journal Letter
High-energy emission from the stellar wind collisions in gamma-2 Velorum
The binary system gamma-2 Velorum (WC8+O7.5) contains the nearest known
Wolf-Rayet star to the Sun, at a distance of 258 pc. Its strong
radio emission shows evidence for a partially absorbed nonthermal component,
which has been interpreted as synchrotron emission from electrons accelerated
in the colliding wind region. Inverse Compton cooling of these electrons in the
intense UV radiation field from the O-type companion star could produce a
significant hard X-ray and gamma-ray emission, whose flux depends on the ratio
of the energy densities of magnetic to seed photon fields. The Vela region was
observed with the INTEGRAL satellite in 2003, as part of the Core Programme. No
signals from gamma-2 Vel are detected in the images obtained with the
IBIS/ISGRI coded aperture instrument in the energy ranges 20-40 and 40-80 keV.
From the derived 3 upper limits, we show that the average magnetic
field near the region of stellar wind collision should be relatively high,
greater than about 1 G. The high-energy emission of gamma-2 Vel might be
detected with the forthcoming GLAST experiment.Comment: 4 pages, 3 figures. To appear in the Proceedings of the 5th INTEGRAL
Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munich, German
L-Convex Polyominoes are Recognizable in Real Time by 2D Cellular Automata
A polyomino is said to be L-convex if any two of its cells are connected by a
4-connected inner path that changes direction at most once. The 2-dimensional
language representing such polyominoes has been recently proved to be
recognizable by tiling systems by S. Brocchi, A. Frosini, R. Pinzani and S.
Rinaldi. In an attempt to compare recognition power of tiling systems and
cellular automata, we have proved that this language can be recognized by
2-dimensional cellular automata working on the von Neumann neighborhood in real
time.
Although the construction uses a characterization of L-convex polyominoes
that is similar to the one used for tiling systems, the real time constraint
which has no equivalent in terms of tilings requires the use of techniques that
are specific to cellular automata
Variation of the X-ray non-thermal emission in the Arches cloud
The origin of the iron fluorescent line at 6.4 keV from an extended region
surrounding the Arches cluster is debated and the non-variability of this
emission up to 2009 has favored the low-energy cosmic-ray origin over a
possible irradiation by hard X-rays. By probing the variability of the Arches
cloud non-thermal emission in the most recent years, including a deep
observation in 2012, we intend to discriminate between the two competing
scenarios. We perform a spectral fit of XMM-Newton observations collected from
2000 to 2013 in order to build the Arches cloud lightcurve corresponding to
both the neutral Fe Kalpha line and the X-ray continuum emissions. We reveal a
30% flux drop in 2012, detected with more than 4 sigma significance for both
components. This implies that a large fraction of the studied non-thermal
emission is due to the reflection of an X-ray transient source.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
SPI Measurements of the Diffuse Galactic Hard X-ray Continuum
INTEGRAL Spectrometer SPI data from the first year of the Galactic Centre
Deep Exposure has been analysed for the diffuse continuum from the Galactic
ridge. A new catalogue of sources from the INTEGRAL Imager IBIS has been used
to account for their contribution to the celestial signal. Apparently diffuse
emission is detected at a level ~10% of the total source flux. A comparison of
the spectrum of diffuse emission with that from an analysis of IBIS data alone
shows that they are consistent. The question of the contribution of unresolved
sources to this ridge emission is still open.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004.
ESA SP-552. Reference to Terrier et al. (2004) updated to include astro-ph
versio
Polarimetric device for images analysis
A method allowing to completely estimate, by camera, the polarization state of a light wave is presented. The characterization
of the light wave and its interaction with the various optical elements constituting the measurement device are described using
the Stokes-Mueller formalism. We are mainly interested in the determination of the polarization state of a light wave reflected
by an object in order to obtain information on this one. Thus, we show that our measurement device can be used to classify
materials according to their conductivity. We also apply our method to classify the facets of the observed object following their
geometrical orientation. Lastly, we are interested in the problem of highlight suppression.
The advantage of the presented method is that it allows to separate the polarized and unpolarized components of the reflected
light wave. So, the proposed system allows to avoid a loss of information about the observed scene and consequently decreases
the ambiguity risk in the interpretation of this information.Nous présentons une méthode permettant de caractériser complètement, par caméra, l'état de polarisation de n'importe quelle onde lumineuse. La caractérisation de l'onde et son interaction avec les différents éléments optiques constituant le dispositif de mesure sont représentés par le formalisme de Stokes-Mueller. Nous nous intéressons principalement à la détermination de l'état de polarisation d'une onde lumineuse réfléchie sur un objet dans le but d'obtenir un certain nombre d'informations sur ce dernier. Ainsi, nous montrons que notre dispositif de mesure peut servir à classifier des matériaux en fonction de leur nature diélectrique ou métallique. Nous appliquons également notre méthode à la classification des facettes de l'objet observé suivant leur orientation géométrique. Enfin, nous nous intéressons au problème de la suppression, dans certaines images, des zones de saturations correspondant à un éblouissement dû à une forte concentration d'énergie. L'avantage de la méthode que nous présentons est qu'elle permet de séparer les composantes polarisées et non polarisées de l'onde réfléchie. Le système proposé permet donc d'éviter une perte du contenu informationnel sur la scène observée et par conséquent diminue le risque d'ambiguité dans l'interprétation de ces informations
Discovery of new TeV supernova remnant shells in the Galactic plane with H.E.S.S
Supernova remnants (SNRs) are prime candidates for efficient particle
acceleration up to the knee in the cosmic ray particle spectrum. In this work
we present a new method for a systematic search for new TeV-emitting SNR shells
in 2864 hours of H.E.S.S. phase I data used for the H.E.S.S. Galactic Plane
Survey. This new method, which correctly identifies the known shell
morphologies of the TeV SNRs covered by the survey, HESS J1731-347, RX
1713.7-3946, RCW 86, and Vela Junior, reveals also the existence of three new
SNR candidates. All three candidates were extensively studied regarding their
morphological, spectral, and multi-wavelength (MWL) properties. HESS J1534-571
was associated with the radio SNR candidate G323.7-1.0, and thus is classified
as an SNR. HESS J1912+101 and HESS J1614-518, on the other hand, do not have
radio or X-ray counterparts that would permit to identify them firmly as SNRs,
and therefore they remain SNR candidates, discovered first at TeV energies as
such. Further MWL follow up observations are needed to confirm that these newly
discovered SNR candidates are indeed SNRs
The XMM-Newton view of the central degrees of the Milky Way
The deepest XMM-Newton mosaic map of the central 1.5 deg of the Galaxy is
presented, including a total of about 1.5 Ms of EPIC-pn cleaned exposures in
the central 15" and about 200 ks outside. This compendium presents broad-band
X-ray continuum maps, soft X-ray intensity maps, a decomposition into spectral
components and a comparison of the X-ray maps with emission at other
wavelengths. Newly-discovered extended features, such as supernova remnants
(SNRs), superbubbles and X-ray filaments are reported. We provide an atlas of
extended features within +-1 degree of Sgr A*. We discover the presence of a
coherent X-ray emitting region peaking around G0.1-0.1 and surrounded by the
ring of cold, mid-IR-emitting material known from previous work as the "Radio
Arc Bubble" and with the addition of the X-ray data now appears to be a
candidate superbubble. Sgr A's bipolar lobes show sharp edges, suggesting that
they could be the remnant, collimated by the circumnuclear disc, of a SN
explosion that created the recently discovered magnetar, SGR J1745-2900. Soft
X-ray features, most probably from SNRs, are observed to fill holes in the dust
distribution, and to indicate a direct interaction between SN explosions and
Galactic center (GC) molecular clouds. We also discover warm plasma at high
Galactic latitude, showing a sharp edge to its distribution that correlates
with the location of known radio/mid-IR features such as the "GC Lobe". These
features might be associated with an inhomogeneous hot "atmosphere" over the
GC, perhaps fed by continuous or episodic outflows of mass and energy from the
GC region.Comment: MNRAS published online. See www.mpe.mpg.de/heg/gc/ for a higher
resolution version of the figure
Persistent fluctuations in stride intervals under fractal auditory stimulation
Copyright @ 2014 Marmelat et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Stride sequences of healthy gait are characterized by persistent long-range correlations, which become anti-persistent in the presence of an isochronous metronome. The latter phenomenon is of particular interest because auditory cueing is generally considered to reduce stride variability and may hence be beneficial for stabilizing gait. Complex systems tend to match their correlation structure when synchronizing. In gait training, can one capitalize on this tendency by using a fractal metronome rather than an isochronous one? We examined whether auditory cues with fractal variations in inter-beat intervals yield similar fractal inter-stride interval variability as isochronous auditory cueing in two complementary experiments. In Experiment 1, participants walked on a treadmill while being paced by either an isochronous or a fractal metronome with different variation strengths between beats in order to test whether participants managed to synchronize with a fractal metronome and to determine the necessary amount of variability for participants to switch from anti-persistent to persistent inter-stride intervals. Participants did synchronize with the metronome despite its fractal randomness. The corresponding coefficient of variation of inter-beat intervals was fixed in Experiment 2, in which participants walked on a treadmill while being paced by non-isochronous metronomes with different scaling exponents. As expected, inter-stride intervals showed persistent correlations similar to self-paced walking only when cueing contained persistent correlations. Our results open up a new window to optimize rhythmic auditory cueing for gait stabilization by integrating fractal fluctuations in the inter-beat intervals.Commission of the European Community and the Netherlands Organisation for Scientific Research
Influenza A viruses alter the stability and antiviral contribution of host E3-ubiquitin ligase Mdm2 during the time-course of infection
International audienceThe interplay between influenza A viruses (IAV) and the p53 pathway has been reported in several studies, highlighting the antiviral contribution of p53. Here, we investigated the impact of IAV on the E3-ubiquitin ligase Mdm2, a major regulator of p53, and observed that IAV targets Mdm2, notably via its non-structural protein (NS1), therefore altering Mdm2 stability, p53/Mdm2 interaction and regulatory loop during the time-course of infection. This study also highlights a new antiviral facet of Mdm2 possibly increasing the list of its many p53-independent functions. Altogether, our work contributes to better understand the mechanisms underlining the complex interactions between IAV and the p53 pathway, for which both NS1 and Mdm2 arise as key players
- …