We report on observations of very high energy {gamma} rays from the shell-type supernova remnant (SNR) Cassiopeia A with the Very Energetic Radiation Imaging Telescope Array System stereoscopic array ...of four imaging atmospheric Cherenkov telescopes in Arizona. The total exposure time for these observations is 22 hr, accumulated between September and November of 2007. The {gamma}-ray source associated with the SNR Cassiopeia A was detected above 200 GeV with a statistical significance of 8.3{sigma}. The estimated integral flux for this {gamma}-ray source is about 3% of the Crab-Nebula flux. The photon spectrum is compatible with a power law dN/dE {proportional_to} E {sup -{Gamma}} with an index {Gamma} = 2.61 {+-} 0.24{sub stat} {+-} 0.2{sub sys}. The data are consistent with a point-like source. We provide a detailed description of the analysis results and discuss physical mechanisms that may be responsible for the observed {gamma}-ray emission.
: Amyloid β‐peptide (Aβ) aggregates are one of the key neuropathological characteristics of Alzheimer's disease. Aβ belongs to a group of proteins that aggregate and form β‐sheets, and some of these ...proteins bind cholesterol and other lipids. The purpose of the experiments reported here was to determine if cholesterol, fatty acids, and phosphatidylcholine (PC) would bind to Aβ1–40 and if such binding would be dependent on aggregation of Aβ1–40. Lipid binding was determined using fluorescent‐labeled lipids. Incubation of Aβ1–40 for 0, 1, 3, 6, 21, and 24 h resulted in aggregation of the peptide with formation of dimers, trimers (1–24 h), and polymers (6–24 h) as determined by sodium dodecyl sulfate‐gel electrophoresis. No change in the fluorescence of the lipids was observed when lipids were added to Aβ1–40 that had been incubated for 0, 1, or 3 h. However, the fluorescence intensities of cholesterol, saturated fatty acids, and PC were significantly increased (p < 0.0001) when added to Aβ1–40 that had been incubated for 6, 21, and 24 h in which Aβ1–40 polymers were detected. The binding affinity of cholesterol to Aβ1–40 polymers (KD of 3.24 ± 0.315 × 10−9M) was markedly higher as compared with the other lipids (stearic acid, 9.42 ± 0.41 × 10−8M; PC, 7.07 ± 0.12 × 10−7M). The results of this study indicate that Aβ1–40 polymers bind lipids and have a higher affinity for cholesterol than PC or saturated fatty acids. Aggregated Aβ1–40 may affect lipid transport between cells or remove specific lipids from membranes, and such effects could contribute to neuronal dysfunction.
We report the detection of very-high-energy (VHE) gamma-ray emission from supernova remnant (SNR) G106.3+2.7. Observations performed in 2008 with the VERITAS atmospheric Cherenkov gamma-ray telescope ...resolve extended emission overlapping the elongated radio SNR. The 7.3sigma (pre-trials) detection has a full angular extent of roughly 0.{sup 0}6 by 0.{sup 0}4. Most notably, the centroid of the VHE emission is centered near the peak of the coincident {sup 12}CO (J = 1-0) emission, 0.{sup 0}4 away from the pulsar PSR J2229+6114, situated at the northern end of the SNR. Evidently the current-epoch particles from the pulsar wind nebula are not participating in the gamma-ray production. The VHE energy spectrum measured with VERITAS is well characterized by a power law dN/dE = N {sub 0}(E/3 TeV){sup -G}AMMA with a differential index of GAMMA = 2.29 +- 0.33{sub stat} +- 0.30{sub sys} and a flux of N{sub 0} = (1.15 +- 0.27{sub stat} +- 0.35{sub sys}) x 10{sup -13} cm{sup -2} s{sup -1} TeV{sup -1}. The integral flux above 1 TeV corresponds to {approx}5 percent of the steady Crab Nebula emission above the same energy. We describe the observations and analysis of the object and briefly discuss the implications of the detection in a multiwavelength context.
For any natural numbers \(k \leq n\), the rational cohomology ring of the space of continuous maps \(S^{2k-1} \to S^{2n-1}\) (respectively, \(S^{4k-1} \to S^{4n-1}\)) equivariant under the Hopf ...action of the circle (respectively, of the group \(S^3\) of unit quaternions) is naturally isomorphic to that of the Stiefel manifold \(V_k({\mathbb C}^n)\) (respectively, \(V_k({\mathbb H}^n)\)). The natural maps of integral cohomology groups of these spaces of equivariant maps to cohomology of Stiefel manifolds are surjective but not injective.
We develop a technique for calculating the cohomology groups of spaces of complex parametric knots in \({\mathbb C}^k\), \(k \geq 3\), and carry out these calculations to obtain these groups of low ...dimensions.
We study the topology of complements of caustics of function singularities of low codimensions, in particular 1) complete the enumeration of connected components of the complements of caustics of ...{\em simple} (in the sense of V.Arnold) singularities, in particular find the numbers of these components for the last two classes, \(E_7\) and \(E_8\), remaining unknown after the works of R.Thom, V.Arnold and V.Sedykh; 2) realize all these components for simple singularities by explicitly constructed functions, and realize their one-dimensional homology and cohomology groups by cycles and cocycles; 3) prove that (in contrast to the case of simple singularities) for some parabolic singularities the two-dimensional homology groups of the complements of their caustics are nontrivial.
We report the detection of very high energy -ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae by VERITAS. The source was observed between 2008 January and April. A ...strong outburst of -ray emission was measured in the middle of March, lasting for only 4 days. The energy spectrum measured during the two highest flare nights is fit by a power law and is found to be very steep, with a differential photon spectral index of image. The integral photon flux above image during those two nights corresponds to roughly image of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron self-Compton (SSC) or external Compton (EC) leptonic jet models.
We present the results of 16 Swift-triggered Gamma-ray burst (GRB) follow-up observations taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) telescope array from 2007 ...January to 2009 June. The median energy threshold and response time of these observations were 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter timescale determined by the maximum VERITAS sensitivity to a burst with a t --1.5 time profile. This temporal model is characteristic of GRB afterglows with high-energy, long-lived emission that have been detected by the Large Area Telescope on board the Fermi satellite. No significant very high energy (VHE) gamma-ray emission was detected and upper limits above the VERITAS threshold energy are calculated. The VERITAS upper limits are corrected for gamma-ray extinction by the extragalactic background light and interpreted in the context of the keV emission detected by Swift. For some bursts the VHE emission must have less power than the keV emission, placing constraints on inverse Compton models of VHE emission.
A (conjecturally complete) list of components of complements of discriminant varieties of parabolic singularities of smooth real functions is given. We also promote a combinatorial program that ...enumerates possible topological types of non-discriminant morsifications of isolated real function singularities and provides a strong invariant of components of complements of discriminant varieties.
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