397 research outputs found
Silicon photomultiplers in Very High Energy gamma-ray astrophysics
In the last ten years silicon photomultipliers (SiPMs) have gained terrain in
experiments and applications in which photomultiplier tubes have been the
dominant photosensors during decades. Imaging Atmospheric Cherenkov Telescopes
(IACTs) for very high energy (VHE, E50 GeV) gamma-ray astronomy are
experiencing the same process. Until now FACT was the only IACT using SiPMs. In
the Cherenkov Telescope Array (CTA), the next-generation VHE gamma-ray
observatory, at least 70 telescopes equipped with SiPMs are planned to be
built. The first prototypes have already been constructed and are now being
commissioned. Here we discuss some of the advantages and drawbacks of using
SiPMs in VHE gamma-ray astronomy and provide a brief overview of different
developments related to the use of SiPMs in IACTs.Comment: Accepted for publication in JINST. 9 pages, 7 figures. Proceedings of
the 5th INFIER
Light-Trap: A SiPM Upgrade for Very High Energy Astronomy and Beyond
With the development of the Imaging Atmospheric Cherenkov Technique (IACT),
Gamma-ray astronomy has become one of the most interesting and productive
fields of astrophysics. Current IACT telescope arrays (MAGIC, H.E.S.S, VERITAS)
use photomultiplier tubes (PMTs) to detect the optical/near-UV Cherenkov
radiation emitted due to the interaction of gamma rays with the atmosphere. For
the next generation of IACT experiments, the possibility of replacing the PMTs
with Silicon photomultipliers (SiPMs) is being studied. Among the main
drawbacks of SiPMs are their limited active area (leading to an increase in the
cost and complexity of the camera readout) and their sensitivity to unwanted
wavelengths. Here we propose a novel method to build a relatively low-cost
pixel consisting of a SiPM attached to a PMMA disc doped with a wavelength
shifter. This pixel collects light over a much larger area than a single
standard SiPM and improves sensitivity to near-UV light while simultaneously
rejecting background. We describe the design of a detector that could also have
applications in other fields where detection area and cost are crucial. We
present results of simulations and laboratory measurements of a pixel prototype
and from field tests performed with a 7-pixel cluster installed in a MAGIC
telescope camera.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea. Id:81
The Mass of the Black Hole in LMC X-3
We analyze a large set of new and archival photometric and spectroscopic
observations of LMC X-3 to arrive at a self-consistent dynamical model for the
system. Using echelle spectra obtained with the MIKE instrument on the 6.5m
Magellan Clay telescope and the UVES instrument on the second 8.2m Very Large
Telescope we find a velocity semiamplitude for the secondary star of
km s, where the uncertainty includes an estimate of
the systematic error caused by X-ray heating. Using the spectra, we also find a
projected rotational velocity of km s.
From an analysis of archival and light curves as well as new and
light curves from the SMARTS 1.3m telescope, we find an inclination of
for models that do not include X-ray heating and an
inclination of for models that incorporate X-ray
heating. Adopting the latter inclination measurement, we find masses of
and for the companion star
and the black hole, respectively. We briefly compare our results with earlier
work and discuss some of their implications.Comment: 31 pages, 15 figures, substantial revisions, ApJ, accepte
Chronic dermatomycoses of the foot as risk factors for acute bacterial cellulitis of the leg: A case-control study
Objective: To assess the role of foot dermatomycosis ( tinea pedis and onychomycosis) and other candidate risk factors in the development of acute bacterial cellulitis of the leg. Methods: A case-control study, including 243 patients ( cases) with acute bacterial cellulitis of the leg and 467 controls, 2 per case, individually matched for gender, age (+/-5 years), hospital and admission date (+/-2 months). Results: Overall, mycology-proven foot dermatomycosis was a significant risk factor for acute bacterial cellulitis (odds ratio, OR: 2.4; p < 0.001), as were tinea pedis interdigitalis (OR: 3.2; p < 0.001), tinea pedis plantaris (OR: 1.7; p = 0.005) and onychomycosis (OR: 2.2; p < 0.001) individually. Other risk factors included: disruption of the cutaneous barrier, history of bacterial cellulitis, chronic venous insufficiency and leg oedema. Conclusions: Tinea pedis and onychomycosis were found to be significant risk factors for acute bacterial cellulitis of the leg that are readily amenable to treatment with effective pharmacological therapy. Copyright (C) 2004 S. Karger AG, Basel
Dissociative Autoionization in (1+2)-photon Above Threshold Excitation of H2 Molecules
We have theoretically studied the effect of dissociative autoionization on
the photoelectron energy spectrum in (1+2)-photon above threshold
ionization(ATI) of H2 molecules. We have considered excitation from the ground
state X-singlet-Sigma-g+(v=0,j) to the doubly excited autoionizing states of
singlet-Sigma-u+ and singlet-Pi-u+ symmetry, via the intermediate resonant
B-singlet-Sigma-u+(v=5,j) states. We have shown that the photoelectron energy
spectrum is oscillatory in nature and shows three distinct peaks above the
photoelectron energy 0.7 eV. This feature has been observed in a recent
experiment by Rottke et al, J. Phys. B, Vol. 30, p-4049 (1997).Comment: 11 pages and 4 figure
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