5,041 research outputs found
Uneindeutig, halbherzig und verwirrend: Warum das Wahlgesetz der Ampel-Koalition kein Fortschritt ist
In diesem Meinungsbeitrag diskutiert der Autor die Reform des Wahlrechts kritisch und erläutert Parteienpositionen und -vorgehensweisen, grundlegende Begriffe (wie bspw. Überhangmandate, Direktmandate) sowie Alternativvorschläge zur Wahlrechtsreform
Parameter constraints for high-energy models of colliding winds of massive stars: the case WR 147
We explore the ability of high energy observations to constrain orbital
parameters of long period massive binary systems by means of an inverse Compton
model acting in colliding wind environments. This is particular relevant for
(very) long period binaries where orbital parameters are often poorly known
from conventional methods, as is the case e.g. for the Wolf-Rayet (WR) star
binary system WR 147 where INTEGRAL and MAGIC upper limits on the high-energy
emission have recently been presented. We conduct a parameter study of the set
of free quantities describing the yet vaguely constrained geometry and
respective effects on the non-thermal high-energy radiation from WR 147. The
results are confronted with the recently obtained high-energy observations and
with sensitivities of contemporaneous high-energy instruments like Fermi-LAT.
For binaries with sufficient long periods, like WR 147, gamma-ray attenuation
is unlikely to cause any distinctive features in the high-energy spectrum. This
leaves the anisotropic inverse Compton scattering as the only process that
reacts sensitively on the line-of-sight angle with respect to the orbital
plane, and therefore allows the deduction of system parameters even from
observations not covering a substantial part of the orbit.
Provided that particle acceleration acts sufficiently effectively to allow
the production of GeV photons through inverse Compton scattering, our analysis
indicates a preference for WR 147 to possess a large inclination angle.
Otherwise, for low inclination angles, electron acceleration is constrained to
be less efficient as anticipated here.Comment: 33 pages, 9 figures; accepted by Ap
TARGET: toward a solution for the readout electronics of the Cherenkov Telescope Array
TARGET is an application specific integrated circuit (ASIC) designed to read
out signals recorded by the photosensors in cameras of very-high-energy
gamma-ray telescopes exploiting the imaging of Cherenkov radiation from
atmospheric showers. TARGET capabilities include sampling at a high rate
(typically 1 GSample/s), digitization, and triggering on the sum of four
adjacent pixels. The small size, large number of channels read out per ASIC
(16), low cost per channel, and deep buffer for trigger latency (~16 s at
1 GSample/s) make TARGET ideally suited for the readout in systems with a large
number of telescopes instrumented with compact photosensors like multi-anode or
silicon photomultipliers combined with dual-mirror optics. The possible
advantages of such systems are better sensitivity, a larger field of view, and
improved angular resolution. The two latest generations of TARGET ASICs, TARGET
5 and TARGET 7, are soon to be used for the first time in two prototypes of
small-sized and medium-sized dual-mirror telescopes proposed in the framework
of the Cherenkov Telescope Array (CTA) project. In this contribution we report
on the performance of the TARGET ASICs and discuss future developments.Comment: 8 pages, 3 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
On the Origin of TeV Gamma-ray Emission from HESS J1834-087
We present an X-ray study of the field containing the extended TeV source
HESS J1834-087 using data obtained with the XMM-Newton telescope. Previously,
the coincidence of this source with both the shell-type supernova remnant (SNR)
W41 and a giant molecular cloud (GMC) was interpreted as favoring pi^0-decay
gamma-rays from interaction of the old SNR with the GMC. Alternatively, the TeV
emission has been attributed to inverse Compton scattering from leptons
deposited by PSR J1833-0827, a pulsar assumed to have been born in W41 but now
located 24' from the center of the SNR (and the TeV source). Instead, we argue
for a third possibility, that the TeV emission is powered by a previously
unknown pulsar wind nebula located near the center of W41. The candidate pulsar
is XMMU J183435.3-084443, a hard X-ray point source that lacks an optical
counterpart to R>21 and is coincident with diffuse X-ray emission. The X-rays
from both the point source and diffuse feature are evidently non-thermal and
highly absorbed. A best fit power-law model yields photon index Gamma ~ 0.2 and
Gamma ~ 1.9, for the point source and diffuse emission, respectively, and 2-10
keV flux ~ 5 X 10^(-13) ergs/cm^(2)/s for each. At the measured 4 kpc distance
of W41, the observed X-ray luminosity implies an energetic pulsar with Edot ~
10^(36)d_4^2 ergs/s, which is also sufficient to generate the observed
gamma-ray luminosity of 2.7 X 10^(34)d_4^2 ergs/s via inverse Compton
scattering.Comment: Accepted for publication in The Astrophysical Journa
Status of Identification of VHE gamma-ray sources
With the recent advances made by Cherenkov telescopes such as H.E.S.S., the
field of very high-energy (VHE) gamma-ray astronomy has recently entered a new
era in which for the first time populations of Galactic sources such as e.g.
Pulsar wind nebulae (PWNe) or Supernova remnants (SNRs) can be studied.
However, while some of the new sources can be associated by positional
coincidence as well as by consistent multi-wavelength data to a known
counterpart at other wavelengths, most of the sources remain not finally
identified. In the following, the population of Galactic H.E.S.S. sources will
be used to demonstrate the status of the identifications, to classify them into
categories according to this status and to point out outstanding problems.Comment: To appear in Astrophysics and Space Science (Proceedings of "The
multimessenger approach to unidentified gamma-ray sources
Ebola virus disease in the Democratic Republic of the Congo, 1976-2014: Figures and Data
The Democratic Republic of the Congo has experienced the most outbreaks of Ebola virus disease since the virus' discovery in 1976. This dataset contains details on all outbreaks in this country, comprising 996 cases. The study found that, compared to patients over 15 years old, the odds of dying were significantly lower in patients aged 5 to 15 and higher in children under five (with 100% mortality in those under 2 years old). The odds of dying increased by 11% per day that a patient was not hospitalised. Outbreaks with an initially high reproduction number, R (>3), were rapidly brought under control, whilst outbreaks with a lower initial R caused longer and generally larger outbreaks. These findings can inform the choice of target age groups for interventions and highlight the importance of both reducing the delay between symptom onset and hospitalisation and rapid national and international response
Broad-band nonthermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants
Molecular clouds are expected to emit non-thermal radiation due to cosmic ray
interactions in the dense magnetized gas. Such emission is amplified if a cloud
is located close to an accelerator of cosmic rays and if energetic particles
can leave the accelerator site and diffusively reach the cloud. We consider
here the situation in which a molecular cloud is located in the proximity of a
supernova remnant which is efficiently accelerating cosmic rays and gradually
releasing them in the interstellar medium. We calculate the multiwavelength
spectrum from radio to gamma rays which is emerging from the cloud as the
result of cosmic ray interactions. The total energy output is dominated by the
gamma ray emission, which can exceed the emission in other bands by an order of
magnitude or more. This suggests that some of the unidentified TeV sources
detected so far, with no obvious or very weak counterparts in other
wavelengths, might be in fact associated with clouds illuminated by cosmic rays
coming from a nearby source. Moreover, under certain conditions, the gamma ray
spectrum exhibit a concave shape, being steep at low energies and hard at high
energies. This fact might have important implications for the studies of the
spectral compatibility of GeV and TeV gamma ray sources.Comment: 13 pages, 6 figures, submitted to MNRA
Automatic Network Fingerprinting through Single-Node Motifs
Complex networks have been characterised by their specific connectivity
patterns (network motifs), but their building blocks can also be identified and
described by node-motifs---a combination of local network features. One
technique to identify single node-motifs has been presented by Costa et al. (L.
D. F. Costa, F. A. Rodrigues, C. C. Hilgetag, and M. Kaiser, Europhys. Lett.,
87, 1, 2009). Here, we first suggest improvements to the method including how
its parameters can be determined automatically. Such automatic routines make
high-throughput studies of many networks feasible. Second, the new routines are
validated in different network-series. Third, we provide an example of how the
method can be used to analyse network time-series. In conclusion, we provide a
robust method for systematically discovering and classifying characteristic
nodes of a network. In contrast to classical motif analysis, our approach can
identify individual components (here: nodes) that are specific to a network.
Such special nodes, as hubs before, might be found to play critical roles in
real-world networks.Comment: 16 pages (4 figures) plus supporting information 8 pages (5 figures
Cavity of Molecular Gas Associated with Supernova Remnant 3C 397
3C 397 is a radio and X-ray bright Galactic supernova remnant (SNR) with an
unusual rectangular morphology. Our CO observation obtained with the Purple
Mountain Observatory at Delingha reveals that the remnant is well confined in a
cavity of molecular gas, and embedded at the edge of a molecular cloud (MC) at
the local standard of rest systemic velocity of ~32 km/s. The cloud has a
column density gradient increasing from southeast to northwest, perpendicular
to the Galactic plane, in agreement with the elongation direction of the
remnant. This systemic velocity places the cloud and SNR 3C 397 at a kinematic
distance of ~10.3 kpc. The derived mean molecular density (~10-30 cm^-3)
explains the high volume emission measure of the X-ray emitting gas. A 12CO
line broadening of the ~32 km/s component is detected at the westmost boundary
of the remnant, which provides direct evidence of the SNR-MC interaction and
suggests multi-component gas there with dense (~10^4 cm^-3) molecular clumps.
We confirm the previous detection of a MC at ~38 km/s to the west and south of
the SNR and argue, based on HI self-absorption, that the cloud is located in
the foreground of the remnant. A list of Galactic SNRs presently known and
suggested to be in physical contact with environmental MCs is appended in this
paper.Comment: ApJ in press, 11 pages, 8 figures and 2 tables. A list of Galactic
SNRs in physical contact with molecular clouds is included; it is updated in
Ver.
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