Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018–589 A that is coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6–5856 have resulted in a source ...detection significance of more than 9σ and the detection of variability (χ2/ν of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018–589 A with the high-energy γ-ray binary detected by Fermi-LAT and also confirms the point-like source as a new VHE binary system. The spectrum of HESS J1018–589 A is best fit with a power-law function with photon index Γ = 2.20 ± 0.14stat ± 0.2sys. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9 ± 0.4) × 10-13 TeV-1 cm-2 s-1 at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of Nσ> 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ ≲ 1 at 300 GeV).
The Fornax galaxy cluster was observed with the Fligh Energy Stereoscopic System for a total live time of 14.5 hr, searching for very high energy (VEIE; E > 100GeV) gamma -rays from dark matter (DM) ...annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section left angle bracketsigmaupsilonright angle bracket as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation gamma -ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional gamma -ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of left angle bracketsigmaupsilonright angle bracket super(95%C.L.) ~ 10 super(-23) cm super(3) s super(-1), depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on left angle bracketsigmaupsilonright angle bracket by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of left angle bracketsigmaupsilonright angle bracket super(95%CL) ~ 10 super(-26) cm super(3) s super(-1).
Expression of the puf and puc operons, which encode proteins of the photosynthetic apparatus of Rhodobacter capsulatus, is regulated by oxygen. A drop in the oxygen tension in the environment leads ...to an increase in the levels of puf and puc mRNAs. In strains lacking bacteriochlorophyll (Bchl) due to mutations in bch genes, the rise in puf and puc mRNA levels observed on reduction of oxygen tension is much less pronounced than in wild-type cells, indicating co-regulation of the syntheses of pigments and pigment-binding proteins. Here we show that Bchl synthesis also affects the expression of the bchC gene, which codes for a subunit of bacteriochlorophyll synthase, suggesting an autoregulatory mechanism for the Bchl biosynthetic pathway. Furthermore, our data provide evidence that the RegB/RegA two-component system, which is known to play a central role in oxygen-controlled expression of photosynthesis genes, is also involved in the Bchl-dependent regulation. Mutant strains which do not synthesize RegB or RegA show similar oxygen-dependent puf and puc expression in the presence and absence of Bchl. Our results support the view that the RegB/RegA system can directly or indirectly sense whether Bchl synthesis takes place or not.
Context. Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E ≳ 100 GeV) ...occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE γ-rays (H.E.S.S.), X-rays (RXTE, Chandra, Swift XRT), optical (Swift UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. Aims. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. Methods. The spectral variability in the X-ray and VHE bands is explored and correlations between the integral fluxes at different wavelengths are evaluated. SSC modelling is used to interpret the general trends of the varying spectral energy distribution. Results. The X-ray and VHE γ-ray emission are correlated during the observed high state of the source, but show no direct connection with longer wavelengths. The long-term flux evolution in the optical and radio bands is found to be correlated and shows that the source reaches a high state at long wavelengths after the occurrence of the VHE flares. Spectral hardening is seen in the Swift XRT data. Conclusions. The nightly averaged high-energy spectra of the non-flaring nights can be reproduced by a stationary one-zone SSC model, with only small variations in the parameters. The spectral and flux evolution in the high-energy band during the night of the second VHE flare is modelled with multi-zone SSC models, which can provide relatively simple interpretations for the hour time-scale evolution of the high-energy emission, even for such a complex data set. For the first time in this type of source, a clear indication is found for a relation between high activity at high energies and a long-term increase in the low frequency fluxes.
The Cherenkov Telescope Array (CTA) consortium aims to build the next-generation ground-based very-high-energy gamma-ray observatory. The array will feature different sizes of telescopes allowing it ...to cover a wide gamma-ray energy band from about 20GeV to above 100TeV. The highest energies, above 5TeV, will be covered by a large number of Small-Sized Telescopes (SSTs) with a field-of-view of around 9°. The Gamma-ray Cherenkov Telescope (GCT), based on Schwarzschild–Couder dual-mirror optics, is one of the three proposed SST designs. The GCT is described in this contribution and the first images of Cherenkov showers obtained using the telescope and its camera are presented. These were obtained in November 2015 in Meudon, 2http://www.cta-observatory.orgFrance.
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•A new method of preparing non-releasing antibacterial biomaterials was developed.•Antibacterial agent was synthesized into a deep eutectic solvent (DES).•DES was linked to the system ...through a covalent bond.•Hydrogen bonding in the DES is beneficial to limit antibacterial agent release.•The developed antibacterial dental composite has good biocompatibility.
To incorporate an antibacterial agent derived deep eutectic solvent (DES) into a dental resin composite, and investigate the resulting mechanical properties and antibacterial effects.
The DES was derived from benzalkonium chloride (BC) and acrylic acid (AA) and was incorporated into the dental resin composite through rapid mixing. A three-point bending test was employed to measure the flexural strength of the composite. An agar diffusion test was used to investigate antibacterial activity. Artificial (accelerated) aging was undertaken by immersing the composites in buffer solutions at an elevated temperature for up to 4 weeks. UV–vis spectrophotometry and NMR analysis were conducted to study BC release from the composite. Finally, the biocompatibility of the composite materials was evaluated using osteoblast cell culture for 7 days. Results were compared to those of a control composite which contained no BC.
The DES-incorporated composite (DES-C) displayed higher flexural strength than a similar BC-incorporated composite BC (BC-C) for the same level of BC. The inclusion of BC conferred antibacterial activity to both BC-containing composites, although BC-C produced larger inhibition halos than DES-C at the same loading of BC. Control composites which contained no BC showed negligible antibacterial activity. After artificial aging, the DES-C composite showed better maintenance of the mechanical properties of the control compared with BC-C, although a decrease was observed during the three-point bending test, particularly upon storage at elevated temperatures. No BC release was detected in the aged solutions of DES-C, whereas the BC-C showed a linear increase in BC release with storage time. Significantly, cell viability results indicated that DES-C has better biocompatibility than BC-C.
The incorporation of a BC-based DES into a dental resin composite provides a new strategy to develop antibacterial dental materials with better biocompatibility and longer effective lifetimes without sacrificing the intrinsic mechanical properties of the composite structure.
Aims. Previous observations with the High Energy Stereoscopic System (H.E.S.S.) have revealed an extended very-high-energy (VHE; E> 100 GeV) γ-ray source, HESS J1834−087, coincident with the ...supernova remnant (SNR) W41. The origin of the γ-ray emission was investigated in more detail with the H.E.S.S. array and the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Methods. The γ-ray data provided by 61 h of observations with H.E.S.S., and four years with the Fermi LAT were analyzed, covering over five decades in energy from 1.8 GeV up to 30 TeV. The morphology and spectrum of the TeV and GeV sources were studied and multiwavelength data were used to investigate the origin of the γ-ray emission toward W41. Results. The TeV source can be modeled with a sum of two components: one point-like and one significantly extended (σTeV = 0.17° ± 0.01°), both centered on SNR W41 and exhibiting spectra described by a power law with index ΓTeV ≃ 2.6. The GeV source detected with Fermi LAT is extended (σGeV = 0.15° ± 0.03°) and morphologically matches the VHE emission. Its spectrum can be described by a power-law model with an index ΓGeV = 2.15 ± 0.12 and smoothly joins the spectrum of the whole TeV source. A break appears in the γ-ray spectra around 100 GeV. No pulsations were found in the GeV range. Conclusions. Two main scenarios are proposed to explain the observed emission: a pulsar wind nebula (PWN) or the interaction of SNR W41 with an associated molecular cloud. X-ray observations suggest the presence of a point-like source (a pulsar candidate) near the center of the remnant and nonthermal X-ray diffuse emission that could arise from the possibly associated PWN. The PWN scenario is supported by the compatible positions of the TeV and GeV sources with the putative pulsar. However, the spectral energy distribution from radio to γ-rays is reproduced by a one-zone leptonic model only if an excess of low-energy electrons is injected following a Maxwellian distribution by a pulsar with a high spin-down power (>1037 erg s-1). This additional low-energy component is not needed if we consider that the point-like TeV source is unrelated to the extended GeV and TeV sources. The interacting SNR scenario is supported by the spatial coincidence between the γ-ray sources, the detection of OH (1720 MHz) maser lines, and the hadronic modeling.
Very high energy (VHE, E > 100 GeV) γ-ray flaring activity of the high-frequency peaked BL Lac object PG 1553+113 has been detected by the H.E.S.S. telescopes. The flux of the source increased by a ...factor of 3 during the nights of 2012 April 26 and 27 with respect to the archival measurements with a hint of intra-night variability. No counterpart of this event has been detected in the Fermi-Large Area Telescope data. This pattern is consistent with VHE γ-ray flaring being caused by the injection of ultrarelativistic particles, emitting γ-rays at the highest energies. The dataset offers a unique opportunity to constrain the redshift of this source at z = 0.49 ± 0.04 using a novel method based on Bayesian statistics. The indication of intra-night variability is used to introduce a novel method to probe for a possible Lorentz invariance violation (LIV), and to set limits on the energy scale at which Quantum Gravity (QG) effects causing LIV may arise. For the subluminal case, the derived limits are E{sub QG,1} > 4.10 × 10{sup 17} GeV and E{sub QG,2} > 2.10 × 10{sup 10} GeV for linear and quadratic LIV effects, respectively.
The active galactic nucleus PKS 0301−243 (z = 0.266) is a high-synchrotron-peaked BL Lac object that is detected at high energies (HE, 100 MeV <E < 100 GeV) by Fermi/LAT. This paper reports on the ...discovery of PKS 0301−243 at very high energies (E > 100 GeV) by the High Energy Stereoscopic System (H.E.S.S.) from observations between September 2009 and December 2011 for a total live time of 34.9 h. Gamma rays above 200 GeV are detected at a significance of 9.4σ. A hint of variability at the 2.5σ level is found. An integral flux I(E > 200 GeV) = (3.3 ± 1.1stat ± 0.7syst) × 10-12 ph cm-2 s-1 and a photon index Γ = 4.6 ± 0.7stat ± 0.2syst are measured. Multi-wavelength light curves in HE, X-ray and optical bands show strong variability, and a minimal variability timescale of eight days is estimated from the optical light curve. A single-zone leptonic synchrotron self-Compton scenario satisfactorily reproduces the multi-wavelength data. In this model, the emitting region is out of equipartition and the jet is particle dominated. Because of its high redshift compared to other sources observed at TeV energies, the very high energy emission from PKS 0301−243 is attenuated by the extragalactic background light (EBL) and the measured spectrum is used to derive an upper limit on the opacity of the EBL.
In this paper we report on the analysis of all the available optical and very high-energy γ-ray (>200 GeV) data for the BL Lac object PKS 2155−304, collected simultaneously with the ATOM and H.E.S.S. ...telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and high-energy γ-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states, and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy γ-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux–colour diagrams, which seem to be related to distinct γ-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and γ-ray emission of PKS 2155−304, with different correlation patterns holding at different epochs, and a γ-ray flux depending on the combination of an optical flux and colour rather than a flux alone.
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