Abstract
Cosmic rays are mostly composed of protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions, which in turn decay into ...gamma-rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum, with a low-energy break around 200 MeV, was detected in the gamma-ray spectra of four supernova remnants (SNRs), IC 443, W44, W49B, and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs. Here, we present a comprehensive search for low-energy spectral breaks among 311 4FGL catalog sources located within 5° from the Galactic plane. Using 8 yr of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV, we find and present the spectral characteristics of 56 sources with a spectral break confirmed by a thorough study of systematic uncertainty. Our population of sources includes 13 SNRs for which the proton–proton interaction is enhanced by the dense target material; the high-mass gamma-ray binary LS I+61 303; the colliding wind binary
η
Carinae; and the Cygnus star-forming region. This analysis better constrains the origin of the gamma-ray emission and enlarges our view to potential new cosmic-ray acceleration sites.
Following the discovery of high-energy (HE; E > 10 MeV) and very-high-energy (VHE; E > 100 GeV) γ-ray emission from the low-frequency-peaked BL Lac (LBL) object AP Librae, its electromagnetic ...spectrum is studied over 60 octaves in energy. Contemporaneous data in radio, optical and UV together with the (non-simultaneous) γ-ray data are used to construct the most precise spectral energy distribution of this source. The data have been found to be modelled with difficulties with single-zone homogeneous leptonic synchrotron self-Compton (SSC) radiative scenarios due to the unprecedented width of the HE component when compared to the lower-energy component. The two other LBL objects also detected at VHE appear to have similar modelling difficulties. Nevertheless, VHE γ-rays produced in the extended jet could account for the VHE flux observed by HESS.
A reanalysis of data taken on the Cygnus region in 1989–90 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032+4130 source reported by the ...Crimean Astrophysical Observatory and published by the HEGRA Collaboration. The significance at the a priori HEGRA position is 3.3σ. The peak signal was found at RA = 20h32m, Dec = +41°33'. This is 0.6° north of Cygnus X-3 which was the original target of the observations. The flux level (12% of the level of the Crab Nebula) is intermediate between the two later observations and suggests that the TeV source is variable.
We present observations of the dwarf galaxies Draco and Ursa Minor, the Local Group galaxies M32 and M33, and the globular cluster M15 conducted with the Whipple 10 m gamma-ray telescope to search ...for the gamma-ray signature of self-annihilating weakly interacting massive particles (WIMPs), which may constitute astrophysical dark matter (DM). We review the motivations for selecting these sources based on their unique astrophysical environments and report the results of the data analysis that produced upper limits on the excess rate of gamma rays for each source. We consider models for the DM distribution in each source based on the available observational constraints and discuss possible scenarios for the enhancement of the gamma-ray luminosity. Limits on the thermally averaged product of the total self- annihilation cross section and velocity of the WIMP, image, are derived using conservative estimates for the magnitude of the astrophysical contribution to the gamma-ray flux. Although these limits do not constrain predictions from the currently favored theoretical models of supersymmetry (SUSY), future observations with VERITAS will probe a larger region of the WIMP parameter phase space, image, and WIMP particle mass.
The well-established technology of electromagnetic calorimetry using Lead Tungstate crystals has recently seen an upheaval, with the closure of one of the most experienced large-scale suppliers of ...such crystals, the Bogoroditsk Technical Chemical Plant (BTCP), which was instrumental in the development of mass production procedures for PWO-II, the current benchmark for this scintillator. Obtaining alternative supplies of Lead Tungstate crystals matching the demanding specifications of contemporary calorimeter devices now presents a significant challenge to detector research and development programmes.
In this paper we describe a programme of assessment carried out for the selection, based upon the performance under irradiation, of Lead Tungstate crystals for use in the Forward Tagger device, part of the CLAS12 detector in Hall B at Jefferson Lab. The crystals tested were acquired from SICCAS, the Shanghai Institute of Ceramics, Chinese Academy of Sciences. The tests performed are intended to maximise the performance of the detector within the practicalities of the crystal manufacturing process.
Results of light transmission, before and after gamma ray irradiation, are presented and used to calculate dk, the induced radiation absorption coefficient, at 420nm, the peak of the Lead Tungstate emission spectrum. Results for the SICCAS crystals are compared with identical measurements carried out on Bogoroditsk samples, which were acquired for the Forward Tagger development program before the closure of the facility.
Also presented are a series of tests performed to determine the feasibility of recovering radiation damage to the crystals using illumination from an LED, with such illumination available in the Forward Tagger from a light monitoring system integral to the detector.
Peritoneal surface epithelial (PSE) cells participate in adhesion formation following inflammatory injury yet adjacent ovarian SE (OSE) cells regenerate without scarification after ovulation. OSE ...cells show inflammation-associated expression of 11beta hydroxysteroid dehydrogenase type 1 (11betaHSD1) enzyme, enabling intracrine generation of anti-inflammatory cortisol to minimise tissue damage. We asked if human PSE cells show an 11betaHSD1 response to pro-/anti-inflammatory stimulation and if so, how the 11-oxoreductase activity generated compares with OSE. PSE collected from premenopausal women undergoing surgery for benign gynaecological conditions were used to establish primary PSE cell cultures that were treated for 48 h with interleukin-1alpha (IL-1alpha) with/without anti-inflammatory steroid (cortisol or progesterone). mRNA levels corresponding to the genes of interest (11betaHSD1, 11betaHSD2, cyclooxygenase-2, COX-2) were measured by quantitative RT-PCR. IL-1alpha (0.5 ng/ml) stimulated 11betaHSD1 and COX-2 mRNA levels in PSE cells but 11betaHSD2 was unaffected. Cortisol (1 microM), not progesterone (1 microM), increased 11betaHSD1 mRNA and synergistically enhanced IL-1alpha action. Cortisol suppressed IL-1alpha-stimulated COX-2 more effectively than progesterone. PSE cells had a significantly lower basal 11-oxoreductase enzyme activity than OSE cells; IL-1alpha did not significantly increase the 11-oxoreductase activity in PSE cells but did so in OSE cells. We conclude that PSE cells respond to IL-1alpha and anti-inflammatory steroids in qualitatively similar ways as OSE. However, the enzymatic activity of 11betaHSD1 is lower in PSE and less responsive to IL-1alpha. This could help explain why peritoneal healing often leads to adhesion formation, whereas postovulatory ovarian healing is scar-free.
Aplanatic telescopes with two aspheric mirrors, configured to correct spherical and coma aberrations, are considered for application in γ-ray astronomy utilizing the ground-based atmospheric ...Cherenkov technique. We explore the phase space of optical system parameters to find telescope configurations which minmize astigmatism. It is shown that unlike the traditional prime-focus Davies-Cotton design, such telescopes provide a solution for wide field of view γ-ray observations.
The designs are isochronous, can be optimized to have no vignetting across the field, and allow for significant reduction of the plate scale, making them compatible with finely-pixilated cameras, which can be constructed from modern, cost-effective image sensors such as multi-anode PMTs, SiPMs, or image intensifiers.
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