400 research outputs found
Constraints on the dust extinction law of the Galaxy with Swift/UVOT, Gaia, and 2MASS
We explore variations of the dust extinction law of the Milky Way by selecting stars from the Swift/UVOT Serendipitous Source Catalogue, cross-matched with Gaia DR2 and 2MASS to produce a sample of 10 452 stars out to ∼4 kpc with photometry covering a wide spectral window. The near ultraviolet passbands optimally encompass the 2175 Å bump, so that we can simultaneously fit the net extinction, quoted in the V band (A_{V}), the steepness of the wavelength dependence (δ), and the bump strength (E_{b}). The methodology compares the observed magnitudes with theoretical stellar atmospheres from the models of Coelho. Significant correlations are found between these parameters, related to variations in dust composition that are complementary to similar scaling relations found in the more complex dust attenuation law of galaxies – that also depend on the distribution of dust among the stellar populations within the galaxy. We recover the strong anticorrelation between AV and Galactic latitude, as well as a weaker bump strength at higher extinction. δ is also found to correlate with latitude, with steeper laws towards the Galactic plane. Our results suggest that variations in the attenuation law of galaxies cannot be fully explained by dust geometry
Autologous Enhancement by Interferon of Natural Killer Activity of Human Peripheral Blood Lymphocytes
The in vitro action of interferon (IFN)-α and
IFN-γ from six healthy donors and ten patients with multiple
sclerosis (MS) on natural killer (INK) activity of peripheral blood
lymphocytes (PBL) was studied in an autologous system. The NK
activity of PBL was detected by a cytotoxic test using
3H-uridine human erythromyeloblast K562 cells. Autologous
IFN-α and IFN-γ did not augment NK activity of PBL from
healthy donors in vitro, whereas in samples from MS
patients the IFNs strongly stimulated NK cell cytotoxic function.
This stimulation suggests the existence of an inhibitor of
regulatory IFN action, that is produced in healthy donors
simultaneously with IFN in response to IFN induction, but which is
lacking in commercial IFN preparations. The factor-containing
supernatants from healthy donors reduced the stimulatory action of
autologous IFNs in patients with MS almost until complete blockade.
Because this inhibitor was absent in patients with MS, deficiency of
an inhibitor of IFN regulatory action in MS could open the way to
treatment of this compartment of the immune system
The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue
Thanks to the large collecting area (3 x ~1500 cm at 1.5 keV) and wide
field of view (30' across in full field mode) of the X-ray cameras on board the
European Space Agency X-ray observatory XMM-Newton, each individual pointing
can result in the detection of hundreds of X-ray sources, most of which are
newly discovered. Recently, many improvements in the XMM-Newton data reduction
algorithms have been made. These include enhanced source characterisation and
reduced spurious source detections, refined astrometric precision, greater net
sensitivity and the extraction of spectra and time series for fainter sources,
with better signal-to-noise. Further, almost 50\% more observations are in the
public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science
Centre (XMM-SSC) to produce a much larger and better quality X-ray source
catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data
automatically and using improved calibration a new catalogue version has been
produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data).
Manual screening ensures the highest data quality. This catalogue is known as
3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections
comprising 396910 unique X-ray sources. For the 133000 brightest sources,
spectra and lightcurves are provided. For all detections, the positions on the
sky, a measure of the quality of the detection, and an evaluation of the X-ray
variability is provided, along with the fluxes and count rates in 7 X-ray
energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To
identify the detections, a cross correlation with 228 catalogues is also
provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source
catalogue ever produced. Thanks to the large array of data products, it is an
excellent resource in which to find new and extreme objects.Comment: 23 pages, version accepted for publication in A&
A new limit of T-violating transverse muon polarization in the decay
A search for T-violating transverse muon polarization () in the
decay was performed using kaon decays at rest. A
new improved value, , was
obtained giving an upper limit, . The T-violation parameter
was determined to be Im giving
an upper limit, Im.Comment: 5 pages, 4 figure
Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry
Here we describe an autonomous way of producing more accurate prompt XRT
positions for Swift-detected GRBs and their afterglows, based on UVOT
astrometry and a detailed mapping between the XRT and UVOT detectors. The
latter significantly reduces the dominant systematic error -- the star-tracker
solution to the World Coordinate System. This technique, which is limited to
times when there is significant overlap between UVOT and XRT PC-mode data,
provides a factor of 2 improvement in the localisation of XRT refined positions
on timescales of less than a few hours. Furthermore, the accuracy achieved is
superior to astrometrically corrected XRT PC mode images at early times (for up
to 24 hours), for the majority of bursts, and is comparable to the accuracy
achieved by astrometrically corrected X-ray positions based on deep XRT PC-mode
imaging at later times (abridged).Comment: 12 pages, 8 figures, 1 table, submitted to Astronomy and
Astrophysics, August 7th 200
Synchronization of the Distributed Readout Frontend Electronics of the Baby MIND Detector
Baby MIND is a new downstream muon range detector for the WGASCI experiment. This article discusses the distributed readout system and its timing requirements. The paper presents the design of the synchronization subsystem and the results of its test
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