1,867 research outputs found
Results from observations of AGNs with the H.E.S.S. telescope system and Future plans
The H.E.S.S. (High Energy Stereoscopic System) phase I is comprised of four
Imaging Atmospheric Cherenkov telescopes, for observation of galactic and
cosmic sources of very high energy gamma rays. Its installation in the Khomas
highlands, Namibia has been completed in December, 2003. The first of these
telescopes was installed in June 2003, and data-taking has proceeded since that
time. The HESS telescope system provides a significant improvement in
sensitivity and a threshold for detection below that of previous Imaging
Atmospheric Cherenkov Telescopes. The characteristics for the phase-I will be
presented, together with plans for phase-II of the experiment, comprised of a
large telescope in the centre of the current phase-I providing a lowered
threshold and increased sensitivity. We can observe AGNs up to redshift 0.5
with HESS and 2-3 with HESS Phase-2, which provides a unique capability for
study of spectral and temporal characteristics on timescales of several hours
or even less than 1 h (depending on the strength of flares). We will present
the first results from a number of southern AGN observed during the
installation of the phase-I, in particular concerning the detection and
spectral properties of the AGN PKS2155305.Comment: To appear in the Springer-Verlag series "ESO Astrophysics Symposia
Central Acceptance Testing for Camera Technologies for CTA
The Cherenkov Telescope Array (CTA) is an international initiative to build
the next generation ground based very-high energy gamma-ray observatory. It
will consist of telescopes of three different sizes, employing several
different technologies for the cameras that detect the Cherenkov light from the
observed air showers. In order to ensure the compliance of each camera
technology with CTA requirements, CTA will perform central acceptance testing
of each camera technology. To assist with this, the Camera Test Facilities
(CTF) work package is developing a detailed test program covering the most
important performance, stability, and durability requirements, including
setting up the necessary equipment. Performance testing will include a wide
range of tests like signal amplitude, time resolution, dead-time determination,
trigger efficiency, performance testing under temperature and humidity
variations and several others. These tests can be performed on fully-integrated
cameras using a portable setup at the camera construction sites. In addition,
two different setups for performance tests on camera sub-units are being built,
which can provide early feedback for camera development. Stability and
durability tests will include the long-term functionality of movable parts,
water tightness of the camera housing, temperature and humidity cycling,
resistance to vibrations during transport or due to possible earthquakes,
UV-resistance of materials and several others. Some durability tests will need
to be contracted out because they will need dedicated equipment not currently
available within CTA. The planned test procedures and the current status of the
test facilities will be presented.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
The H.E.S.S. extragalactic sky
The H.E.S.S. Cherenkov telescope array, located on the southern hemisphere in
Namibia, studies very high energy (VHE; E>100 GeV) gamma-ray emission from
astrophysical objects. During its successful operations since 2002 more than 80
galactic and extra-galactic gamma-ray sources have been discovered. H.E.S.S.
devotes over 400 hours of observation time per year to the observation of
extra-galactic sources resulting in the discovery of several new sources,
mostly AGNs, and in exciting physics results e.g. the discovery of very rapid
variability during extreme flux outbursts of PKS 2155-304, stringent limits on
the density of the extragalactic background light (EBL) in the near-infrared
derived from the energy spectra of distant sources, or the discovery of
short-term variability in the VHE emission from the radio galaxy M 87. With the
recent launch of the Fermi satellite in 2008 new insights into the physics of
AGNs at GeV energies emerged, leading to the discovery of several new
extragalactic VHE sources. Multi-wavelength observations prove to be a powerful
tool to investigate the production mechanism for VHE emission in AGNs. Here,
new results from H.E.S.S. observations of extragalactic sources will be
presented and their implications for the physics of these sources will be
discussed.Comment: 8 pages, 6 figures, invited review talk, in the proceedings of the
"International Workshop on Beamed and Unbeamed Gamma-Rays from Galaxies"
11-15 April 2011, Lapland Hotel Olos, Muonio, Finland, Journal of Physics:
Conference Series Volume 355, 201
New AGNs discovered by H.E.S.S
During the last year, six new Active Galactic Nuclei (AGN) have been
discovered and studied by H.E.S.S. at Very High Energies (VHE). Some of these
recent discoveries have been made thanks to new enhanced analysis methods and
are presented at this conference for the first time. The three blazars 1ES
0414+009, SHBL J001355.9-185406 and 1RXS J101015.9-311909 have been targeted
for observation due to their high levels of radio and X-ray fluxes, while the
Fermi/LAT catalogue of bright sources triggered the observation of PKS 0447-439
and AP Librae. Additionally, the BL Lac 1ES 1312-423 was discovered in the
field-of-view (FoV) of Centaurus A thanks to the large exposure dedicated by
H.E.S.S. to this particularly interesting source. The newly-discovered sources
are presented here and in three companion presentations at this conference.Comment: 8 pages, 3 figures, proceeding from the 25th Texas Symposium on
Relativistic Astrophysics (Heidelberg, Germany, 2010
Care of bullet-related injuries: A cross-sectional study of instructions and prescriptions provided on discharge from the emergency department
INTRODUCTION: There are more than 80,000 emergency department (ED) visits for non-fatal bullet-related injuries (BRI) per year in the United States. Approximately half of these patients are discharged home from the ED. Our objective in this study was to characterize the discharge instructions, prescriptions, and follow-up plans provided to patients discharged from the ED after BRI.
METHODS: This was a single-center, cross-sectional study of the first 100 consecutive patients who presented to an urban, academic, Level I trauma center ED with an acute BRI beginning on January 1, 2020. We queried the electronic health record for patient demographics, insurance status, cause of injury, hospital arrival and discharge timestamps, discharge prescriptions, and documented instructions regarding wound care, pain management, and follow-up plans. We analyzed data using descriptive statistics and chi-square tests.
RESULTS: During the study period, 100 patients presented to the ED with an acute firearm injury. Patients were predominantly young (median age 29, interquartile range 23-38 years), male (86%), Black (85%), non-Hispanic (98%), and uninsured (70%). We found that 12% of patients did not receive any type of written wound care instruction, while 37% received discharge paperwork that included instructions to take both an NSAID and acetaminophen. Fifty-one percent of patients received an opioid prescription, with a range from 3-42 tablets (median 10 tablets). The proportion of patients receiving an opioid prescription was significantly higher among White patients (77%) than among Black patients (47%).
CONCLUSION: There is variability in prescriptions and instructions provided to survivors of bullet injuries upon ED discharge at our institution. Our data indicates that standardized discharge protocols could improve quality of care and equity in the treatment of patients who have survived a BRI. Current variable quality in discharge planning is an entry point for structural racism and disparity
Design of light concentrators for Cherenkov telescope observatories
The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray
detector ever built in the world. It will be installed at two different sites
in the North and South hemispheres and should be operational for about 30
years. In order to cover the desired energy range, the CTA is composed of
typically 50-100 collecting telescopes of various sizes (from 6 to 24-m
diameters). Most of them are equipped with a focal plane camera consisting of
1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics,
whose double function is to maximize the amount of Cherenkov light detected by
the photo-sensors, and to block any stray light originating from the
terrestrial environment. Two different optical solutions have been designed,
respectively based on a Compound Parabolic Concentrator (CPC), and on a purely
dioptric concentrating lens. In this communication are described the technical
specifications, optical designs and performance of the different solutions
envisioned for all these light concentrators. The current status of their
prototyping activities is also given
A Spectacular VHE Gamma-Ray Outburst from PKS 2155-304 in 2006
Since 2002 the VHE (>100 GeV) gamma-ray flux of the high-frequency peaked BL
Lac PKS 2155-304 has been monitored with the High Energy Stereoscopic System
(HESS). An extreme gamma-ray outburst was detected in the early hours of July
28, 2006 (MJD 53944). The average flux above 200 GeV observed during this
outburst is ~7 times the flux observed from the Crab Nebula above the same
threshold. Peak fluxes are measured with one-minute time scale resolution at
more than twice this average value. Variability is seen up to ~600 s in the
Fourier power spectrum, and well-resolved bursts varying on time scales of ~200
seconds are observed. There are no strong indications for spectral variability
within the data. Assuming the emission region has a size comparable to the
Schwarzschild radius of a ~10^9 solar mass black hole, Doppler factors greater
than 100 are required to accommodate the observed variability time scales.Comment: 4 pages, 3 figures; To appear in the Proceedings of the 30th ICRC
(Merida, Mexico
Beings in their own right? Exploring Children and young people's sibling and twin relationships in the Minority World
This paper examines the contributions that the sociological study of sibship and twinship in the Minority World can make to childhood studies. It argues that, in providing one forum within which to explore children and young people's social relationships, we can add to our understanding of children and young people's interdependence and develop a more nuanced understanding of agency. As emergent subjects, children, young people and adults are in a process of âbecomingâ. However, this does not mean that they can âbecomeâ anything they choose to. The notion of negotiated interdependence (Punch 2002) is useful in helping us to grasp the contingent nature of children and young people's agency
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