We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is ...observed, confirming the presence of the so-called
second-knee
feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By ...using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between
2
×
10
17
and
2
×
10
18
eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at
10
17.5
eV
and
10
18
eV
. We find that, for the models to explain the data, an increase in the muon density of
38
%
±
4
%
(
12
%
)
±
18
%
21
%
for
EPOS-LHC
, and of
50
%
(
53
%
)
±
4
%
(
13
%
)
±
20
%
23
%
for
QGSJetII-04
, is respectively needed.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA recently reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the ...spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly discovered features may offer a clue to the origin of high-energy CRs. Here, we use the Fermi Large Area Telescope observations of the γ -ray emission from Earth’s limb for an indirect measurement of the local spectrum of CR protons in the energy range ~ 90 GeV – 6 TeV (derived from a photon energy range 15 GeV–1 TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index 2.68 ± 0.04 and 2.61 ± 0.08 above ~ 200 GeV , respectively.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Here, we present a catalog of γ-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 yr of the Fermi Gamma-ray Space Telescope ...mission. The first Fermi-LAT catalog of >10 GeV sources (1FHL) has 514 sources. For each source we present location, spectrum, a measure of variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. Of the 27 sources associated with known pulsars, we find 20 (12) to have significant pulsations in the range >10 GeV (>25 GeV). In this work we also report that, at energies above 10 GeV, unresolved sources account for 27% ± 8% of the isotropic γ-ray background, while the unresolved Galactic population contributes only at the few percent level to the Galactic diffuse background. We also highlight the subset of the 1FHL sources that are best candidates for detection at energies above 50-100 GeV with current and future ground-based γ-ray observatories.
Weakly interacting massive particles (WIMPs) are a theoretical class of particles that are excellent dark matter candidates. WIMP annihilation or decay may produce essentially monochromatic γ rays ...detectable by the Fermi Large Area Telescope (LAT) against the astrophysical γ -ray emission of the Galaxy. We have searched for spectral lines in the energy range 5–300 GeV using 3.7 years of data, reprocessed with updated instrument calibrations and an improved energy dispersion model compared to the previous Fermi-LAT Collaboration line searches. We searched in five regions selected to optimize sensitivity to different theoretically motivated dark matter density distributions. We did not find any globally significant lines in our a priori search regions and present 95% confidence limits for annihilation cross sections of self-conjugate WIMPs and decay lifetimes. Our most significant fit occurred at 133 GeV in our smallest search region and had a local significance of 3.3 standard deviations, which translates to a global significance of 1.5 standard deviations. We discuss potential systematic effects in this search, and examine the feature at 133 GeV in detail. We find that the use both of reprocessed data and of additional information in the energy dispersion model contributes to the reduction in significance of the linelike feature near 130 GeV relative to significances reported in other works. We also find that the feature is narrower than the LAT energy resolution at the level of 2 to 3 standard deviations, which somewhat disfavors the interpretation of the 133 GeV feature as a real WIMP signal.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Current theories predict relativistic hadronic particle populations in clusters of galaxies in addition to the already observed relativistic leptons. In these scenarios hadronic interactions give ...rise to neutral pions which decay into gamma rays that are potentially observable with the Large Area Telescope (LAT) on board the Fermi space telescope. We present a joint likelihood analysis searching for spatially extended gamma-ray emission at the locations of 50 galaxy clusters in four years of Fermi-LAT data under the assumption of the universal cosmic-ray (CR) model proposed by Pinzke & Pfrommer. We find an excess at a significance of 2.7sigma, which upon closer inspection, however, is correlated to individual excess emission toward three galaxy clusters: A400, A1367, and A3112. We discuss these cases in detail and conservatively attribute the emission to unmodeled background systems (for example, radio galaxies within the clusters). Through the combined analysis of 50 clusters, we exclude hadronic injection efficiencies in simple hadronic models above 21% and establish limits on the CR to thermal pressure ratio within the virial radius, R sub(200), to be below 1.25%-1.4% depending on the morphological classification. In addition, we derive new limits on the gamma-ray flux from individual clusters in our sample.
BACKGROUND:Although halo gravity traction (HGT) has been used to treat children with severe spinal deformity for decades, there is a distinct lack of high-quality evidence to speak to its merits or ...to dictate ideal manner of implementation. In addition, no guidelines exist to drive research or assist surgeons in their practice. The aim of this study was to establish best practice guidelines (BPG) using formal techniques of consensus building among a group of experienced pediatric spinal deformity surgeons to determine ideal indications and implementation of HGT for pediatric spinal deformity.
METHODS:The Delphi process and nominal group technique were used to formally derive consensus among leaders in pediatric spine surgery. Initial work identified significant areas of variability in practice for which we sought to garner consensus. After review of the literature, 3 iterative surveys were administered from February through April 2018 to nationwide experts in pediatric spinal deformity. Surveys assessed anonymous opinions on ideal practices for indications, preoperative evaluation, protocols, and complications, with agreement of 80% or higher considered consensus. Final determination of consensus items and equipoise were established using the Nominal group technique in a facilitated meeting.
RESULTS:Of the 42 surgeons invited, responses were received from 32, 40, and 31 surgeons for each survey, respectively. The final meeting included 14 experts with an average 10.5 years in practice and average 88 annual spinal deformity cases. Experts reached consensus on 67 items indications (17), goals (1), preoperative evaluations (5), protocols (36), complications (8); these were consolidated to create final BPG in all categories, including statements to help dictate practice such as using at least 6 to 8 pins under 4 to 8 lbs of torque, with a small, tolerable starting weight and reaching goal weight of 50% TBW in ∼2 weeks. Nine items remained items of equipoise for the purposes of guiding future research.
CONCLUSIONS:We developed consensus-based BPG for the use and implementation of HGT for pediatric spinal deformity. This can serve as a measure to help drive future research as well as give new surgeons a place to begin their practice of HGT.
LEVEL OF EVIDENCE:Level V—expert opinion.
Background
In contrast with treatment recommendations for adolescent idiopathic scoliosis, there are no clear algorithms for treating patients with early-onset scoliosis. There has been rapid ...expansion of treatment options for children with early-onset scoliosis, including casting, growth rods, the vertical expandable prosthetic titanium rib, and anterior vertebral stapling.
Questions/purposes
Given the range of treatment options, we assessed variability in decision making regarding treatment of patients with early-onset scoliosis.
Methods
We presented 12 clinical and radiographic vignettes about patients with early-onset scoliosis to 13 experienced spine surgeons who are members of the Chest Wall and Spine Deformity Study Group. The reviewers were asked to choose type of treatment, type of construct, construct location, and whether a thoracotomy should be performed.
Results
All 13 surgeons agreed regarding the need for surgery in eight of the 12 cases. When the reviewers chose surgery, 76% (40%–100%) selected the vertical expandable prosthetic titanium rib; of those selecting that approach, 61% (0%–100%) coincided on using it bilaterally. Agreement was 20% (0%–60%) for growing rods and 4% (0%–25%) for fusions. Among all cases, agreement regarding whether instrumentation should extend to the pelvis was 71% (50%–100%). In all but two cases, at least 85% of surgeons recommended against a thoracotomy.
Conclusions
Although most surgeons agreed about the indication for surgery, we found wide variability in choice of construct type, number of constructs, and level of instrumentation.
It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our ...line of sight. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (g)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and g-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 10 super(5) gravitational radii.
Full text
Available for:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
PDF
