136 research outputs found
A systematic analysis of the XMM-Newton background: III. Impact of the magnetospheric environment
A detailed characterization of the particle induced background is fundamental
for many of the scientific objectives of the Athena X-ray telescope, thus an
adequate knowledge of the background that will be encountered by Athena is
desirable. Current X-ray telescopes have shown that the intensity of the
particle induced background can be highly variable. Different regions of the
magnetosphere can have very different environmental conditions, which can, in
principle, differently affect the particle induced background detected by the
instruments. We present results concerning the influence of the magnetospheric
environment on the background detected by EPIC instrument onboard XMM-Newton
through the estimate of the variation of the in-Field-of-View background excess
along the XMM-Newton orbit. An important contribution to the XMM background,
which may affect the Athena background as well, comes from soft proton flares.
Along with the flaring component a low-intensity component is also present. We
find that both show modest variations in the different magnetozones and that
the soft proton component shows a strong trend with the distance from Earth.Comment: To appear in Experimental Astronomy. Presented at AHEAD Background
Workshop, 28-30 November 2016. Rome, Ital
A Systematic Analysis of the XMM-Newton Background: I. Dataset and Extraction Procedures
XMM-Newton is the direct precursor of the future ESA ATHENA mission. A study
of its particle-induced background provides therefore significant insight for
the ATHENA mission design. We make use of about 12 years of data, products from
the third XMM-Newton catalog as well as FP7 EXTraS project to avoid celestial
sources contamination and to disentangle the different components of the
XMM-Newton particle-induced background. Within the ESA R&D AREMBES
collaboration, we built new analysis pipelines to study the different
components of this background: this covers time behavior as well as spectral
and spatial characteristics.Comment: To appear in Experimental Astronomy, presented at AHEAD Background
Workshop, 28-30 November 2016, Rome, Italy. 12 pages, 6 figure
Treatment of food processing wastes for the production of medium chain fatty acids via chain elongation
The production of medium chain fatty acids (MCFAs) through reverse β-oxidation was investigated both on synthetic and real substrates. From preliminary batch tests emerged that caproic acid was maximized under an acetate/ethanol molar ratio of 5:1 at neutral pH. This ratio was then adopted in different semi-continuous tests operating with different amounts of the two reactants. It emerged that the MCFAs yield reached the maximum level of 6.7% when the total molar substrate amount was around 40–45 mmol/d, while the process was inhibited for values higher than 400 mmol/d. Semi-continuous tests using real waste as substrates, namely food waste condensate, cheese whey, and winery wastewater, confirmed the results obtained with the synthetic substrates. Better performances were obtained when an adequate molar ratio of the acetate and the electron-donor compound was naturally present. Therefore, a MCFAs yield of 25% and 10.5% was obtained for condensate of food waste and acidic cheese whey, respectively. Regarding MCFAs composition, caproic acid was the dominant form but small concentrations of octanoic acid were also found in the tests where ethanol was the electron donor (synthetic substrates and food waste condensate). Octanoic acid was not produced in test where lactic acid represented the electron donor molecules (cheese whey). Condensate and synthetic samples were dominated by Pseudoclavibacter caeni with an abundance of 38.19% and 33.38% respectively, while Thomasclavelia (24.13%) and Caproiciproducens (11.68%) was the most representative genus in acidic cheese whey sample
The two tails of PSR J2055+2539 as seen by Chandra: analysis of the nebular morphology and pulsar proper motion
We analyzed two Chandra observations of PSR J2055+2539 (for a total
integration time of 130 ks) in order to measure its proper motion and
study its two elongated nebular features. We did not detect the proper motion,
setting an upper limit of 240 mas yr (3 level), that translates
into an upper limit on the transverse velocity of 700 km s, for an
assumed distance of 600 pc. A deep H observation did not reveal the
bow-shock associated with a classical pulsar wind nebula, thus precluding an
indirect measurement of the proper motion direction. We determined the main
axes of the two nebulae, which are separated by an angle of 160.8, using a new approach based on the Rolling Hough Transformation
(RHT). We analyzed the shape of the first 8' (out of the 12' seen by
XMM-Newton) of the brighter, extremely collimated one. Based on a combination
of our results from a standard analysis and a nebular modeling obtained from
the RHT, we find that the brightest nebula is curved on an arcmin-scale, with a
thickness ranging from " to " and a possible (single or
multiple) helicoidal pattern. We could not constrain the shape of the fainter
nebula. We discuss our results in the context of other known similar features,
with particular emphasis on the Lighthouse nebula (associated with PSR
J11016101). We speculate that a peculiar geometry of the powering pulsar may
play an important role in the formation of such features.Comment: 12 pages, 9 figures, 1 table; accepted by Astronomy & Astrophysic
Chemokine transport across human vascular endothelial cells
Leukocyte migration across vascular endothelium is mediated by chemokines that are either synthesized by the endothelium or transferred across the endothelium from the tissue. The mechanism of transfer of two chemokines, CXCL10 (interferon gamma inducible protein [IP]-10) and CCL2 (macrophage chemotactic protein [MCP]-1), was compared across dermal and lung microvessel endothelium and saphenous vein endothelium. The rate of transfer depended on both the type of endothelium and the chemokine. The permeability coefficient (Pe) for CCL2 movement across saphenous vein was twice the value for dermal endothelium and four times that for lung endothelium. In contrast, the Pe value for CXCL10 was lower for saphenous vein endothelium than the other endothelia. The differences in transfer rate between endothelia was not related to variation in paracellular permeability using a paracellular tracer, inulin, and immunoelectron microscopy showed that CXCL10 was transferred from the basal membrane in a vesicular compartment, before distribution to the apical membrane. Although all three endothelia expressed high levels of the receptor for CXCL10 (CXCR3), the transfer was not readily saturable and did not appear to be receptor dependent. After 30 min, the chemokine started to be reinternalized from the apical membrane in clathrin-coated vesicles. The data suggest a model for chemokine transcytosis, with a separate pathway for clearance of the apical surface
Activity and rotation of the X-ray emitting Kepler stars
The relation between magnetic activity and rotation in late-type stars
provides fundamental information on stellar dynamos and angular momentum
evolution. Rotation/activity studies found in the literature suffer from
inhomogeneity in the measure of activity indexes and rotation periods. We
overcome this limitation with a study of the X-ray emitting late-type
main-sequence stars observed by XMM-Newton and Kepler. We measure rotation
periods from photometric variability in Kepler light curves. As activity
indicators, we adopt the X-ray luminosity, the number frequency of white-light
flares, the amplitude of the rotational photometric modulation, and the
standard deviation in the Kepler light curves. The search for X-ray flares in
the light curves provided by the EXTraS (Exploring the X-ray Transient and
variable Sky) FP-7 project allows us to identify simultaneous X-ray and
white-light flares. A careful selection of the X-ray sources in the Kepler
field yields 102 main-sequence stars with spectral types from A to M. We find
rotation periods for 74 X-ray emitting main-sequence stars, 22 of which without
period reported in the previous literature. In the X-ray activity/rotation
relation, we see evidence for the traditional distinction of a saturated and a
correlated part, the latter presenting a continuous decrease in activity
towards slower rotators. For the optical activity indicators the transition is
abrupt and located at a period of ~ 10 d but it can be probed only marginally
with this sample which is biased towards fast rotators due to the X-ray
selection. We observe 7 bona-fide X-ray flares with evidence for a white-light
counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of
~ 0.15 d^{-1} , consistent with the optical flare frequency obtained from the
much longer Kepler time-series.Comment: Accepted for publication in A&A. 31 pages, 19 figure
EXTraS discovery of a peculiar flaring X-ray source in the Galactic globular cluster NGC 6540
We report the discovery of a flaring X-ray source in the globular cluster NGC
6540, obtained during the EXTraS project devoted to a systematic search for
variability in archival data of the XMM-Newton satellite. The source had a
quiescent X-ray luminosity of the order of ~10^32 erg/s in the 0.5-10 keV range
(for a distance of NGC 6540 of 4 kpc) and showed a flare lasting about 300 s.
During the flare, the X-ray luminosity increased by more than a factor 40, with
a total emitted energy of ~10^36 erg. These properties, as well as Hubble Space
Telescope photometry of the possible optical counterparts, suggest the
identification with a chromospherically active binary. However, the flare
luminosity is significantly higher than what commonly observed in stellar
flares of such a short duration, leaving open the possibility of other
interpretations.Comment: To appear in Astronomy and Astrophysic
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