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  • Abdalla, H., et al. (författare)
  • HESS J1741-302 : a hidden accelerator in the Galactic plane
  • 2018
  • Ingår i: Astronomy and Astrophysics. - EDP Sciences. - 0004-6361. ; 612
  • Tidskriftsartikel (refereegranskat)abstract
    • The H.E.S.S. Collaboration has discovered a new very high energy (VHE, E > 0.1 TeV) gamma-ray source, HESS J1741-302, located in the Galactic plane. Despite several attempts to constrain its nature, no plausible counterpart has been found so far at X-ray and MeV/GeV gamma-ray energies, and the source remains unidentified. An analysis of 145-h of observations of HESS J1741-302 at VHEs has revealed a steady and relatively weak TeV source (similar to 1% of the Crab Nebula flux), with a spectral index of Gamma = 2.3 +/- 0.2(stat) +/- 0.2(sys), extending to energies up to 10 TeV without any clear signature of a cut-off. In a hadronic scenario, such a spectrum implies an object with particle acceleration up to energies of several hundred TeV. Contrary to most H.E.S.S. unidentified sources, the angular size of HESS J1741-302 is compatible with the H.E.S.S. point spread function at VHEs, with an extension constrained to be below 0.068 degrees at a 99% confidence level. The gamma-ray emission detected by H.E.S.S. can be explained both within a hadronic scenario, due to collisions of protons with energies of hundreds of TeV with dense molecular clouds, and in a leptonic scenario, as a relic pulsar wind nebula, possibly powered by the middle-aged (20 kyr) pulsar PSR B1737-30. A binary scenario, related to the compact radio source 1LC 358.266+0.038 found to be spatially coincident with the best fit position of HESS J1741-302, is also envisaged.
  • Anney, R. J. L., et al. (författare)
  • Meta-analysis of GWAS of over 16,000 individuals with autism spectrum disorder highlights a novel locus at 10q24.32 and a significant overlap with schizophrenia
  • 2017
  • Ingår i: Molecular Autism. - 2040-2392. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Over the past decade genome-wide association studies (GWAS) have been applied to aid in the understanding of the biology of traits. The success of this approach is governed by the underlying effect sizes carried by the true risk variants and the corresponding statistical power to observe such effects given the study design and sample size under investigation. Previous ASD GWAS have identified genome-wide significant (GWS) risk loci; however, these studies were of only of low statistical power to identify GWS loci at the lower effect sizes (odds ratio (OR) < 1.15). Methods: We conducted a large-scale coordinated international collaboration to combine independent genotyping data to improve the statistical power and aid in robust discovery of GWS loci. This study uses genome-wide genotyping data from a discovery sample (7387 ASD cases and 8567 controls) followed by meta-analysis of summary statistics from two replication sets (7783 ASD cases and 11359 controls; and 1369 ASD cases and 137308 controls). Results: We observe a GWS locus at 10q24.32 that overlaps several genes including PITX3, which encodes a transcription factor identified as playing a role in neuronal differentiation and CUEDC2 previously reported to be associated with social skills in an independent population cohort. We also observe overlap with regions previously implicated in schizophrenia which was further supported by a strong genetic correlation between these disorders (Rg = 0.23; P= 9 x10(-6)). We further combined these Psychiatric Genomics Consortium (PGC) ASD GWAS data with the recent PGC schizophrenia GWAS to identify additional regions which may be important in a common neurodevelopmental phenotype and identified 12 novel GWS loci. These include loci previously implicated in ASD such as FOXP1 at 3p13, ATP2B2 at 3p25.3, and a 'neurodevelopmental hub' on chromosome 8p11.23. Conclusions: This study is an important step in the ongoing endeavour to identify the loci which underpin the common variant signal in ASD. In addition to novel GWS loci, we have identified a significant genetic correlation with schizophrenia and association of ASD with several neurodevelopmental- related genes such as EXT1, ASTN2, MACROD2, and HDAC4.
  • Abdalla, H., et al. (författare)
  • Detection of very-high-energy gamma-ray emission from the colliding wind binary eta Car with HESS
  • 2020
  • Ingår i: Astronomy and Astrophysics. - EDP Sciences. - 0004-6361 .- 1432-0746. ; 635, s. 1-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. Colliding wind binary systems have long been suspected to be high-energy (HE; 100 MeV &lt; E &lt; 100 GeV) gamma-ray emitters. eta Car is the most prominent member of this object class and is confirmed to emit phase-locked HE gamma rays from hundreds of MeV to 100 GeV energies. This work aims to search for and characterise the very-high-energy (VHE; E &gt;100 GeV) gamma-ray emission from eta Car around the last periastron passage in 2014 with the ground-based High Energy Stereoscopic System (H.E.S.S.).Methods. The region around eta Car was observed with H.E.S.S. between orbital phase p = 0.78-1.10, with a closer sampling at p approximate to 0.95 and p approximate to 1.10 (assuming a period of 2023 days). Optimised hardware settings as well as adjustments to the data reduction, reconstruction, and signal selection were needed to suppress and take into account the strong, extended, and inhomogeneous night sky background (NSB) in the eta Car field of view. Tailored run-wise Monte-Carlo simulations (RWS) were required to accurately treat the additional noise from NSB photons in the instrument response functions.Results. H.E.S.S. detected VHE gamma-ray emission from the direction of eta Car shortly before and after the minimum in the X-ray light-curve close to periastron. Using the point spread function provided by RWS, the reconstructed signal is point-like and the spectrum is best described by a power law. The overall flux and spectral index in VHE gamma rays agree within statistical and systematic errors before and after periastron. The gamma-ray spectrum extends up to at least 400 GeV. This implies a maximum magnetic field in a leptonic scenario in the emission region of 0.5 Gauss. No indication for phase-locked flux variations is detected in the H.E.S.S. data.
  • Abdalla, H., et al. (författare)
  • Searches for gamma-ray lines and 'pure WIMP' spectra from Dark Matter annihilations in dwarf galaxies with HESS
  • 2018
  • Ingår i: Journal of Cosmology and Astroparticle Physics. - Institute of Physics Publishing (IOPP). - 1475-7516. ; :11
  • Tidskriftsartikel (refereegranskat)abstract
    • Dwarf spheroidal galaxies are among the most promising targets for detecting signals of Dark Matter (DM) annihilations. The H.E.S.S. experiment has observed five of these systems for a total of about 130 hours. The data are re-analyzed here, and, in the absence of any detected signals, are interpreted in terms of limits on the DM annihilation cross section. Two scenarios are considered: i) DM annihilation into mono-energetic gamma-rays and ii) DM in the form of pure WIMP multiplets that, annihilating into all electroweak bosons, produce a distinctive gamma-ray spectral shape with a high-energy peak at the DM mass and a lower-energy continuum. For case i), upper limits at 95% confidence level of about &lt;sigma upsilon &gt; less than or similar to 3 x 10(-25) cm(3) s(-1) are obtained in the mass range of 400 GeV to 1TeV. For case ii), the full spectral shape of the models is used and several excluded regions are identified, but the thermal masses of the candidates are not robustly ruled out.
  • Edgecock, T. R., et al. (författare)
  • High intensity neutrino oscillation facilities in Europe
  • 2013
  • Ingår i: Physical Review Special Topics. Accelerators and Beams. - American Physical Society. - 1098-4402. ; 16:2, s. 021002
  • Tidskriftsartikel (refereegranskat)abstract
    • The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Frejus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of mu(+) and mu(-) beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular He-6 and Ne-18, also stored in a ring. The far detector is also the MEMPHYS detector in the Frejus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.
  • Meyer, H.F., et al. (författare)
  • Overview of physics studies on ASDEX Upgrade
  • 2019
  • Ingår i: Nuclear Fusion. - 0029-5515. ; 59:11
  • Forskningsöversikt (refereegranskat)abstract
    • The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
  • Abdalla, H., et al. (författare)
  • A very-high-energy component deep in the gamma-ray burst afterglow
  • 2019
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836. ; 575:7783, s. 464-467
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma-ray bursts (GRBs) are brief flashes of gamma-rays and are considered to be the most energetic explosive phenomena in the Universe(1). The emission from GRBs comprises a short (typically tens of seconds) and bright prompt emission, followed by a much longer afterglow phase. During the afterglow phase, the shocked outflow-produced by the interaction between the ejected matter and the circumburst medium-slows down, and a gradual decrease in brightness is observed(2). GRBs typically emit most of their energy via.-rays with energies in the kiloelectronvolt-to-megaelectronvolt range, but a few photons with energies of tens of gigaelectronvolts have been detected by space-based instruments(3). However, the origins of such high-energy (above one gigaelectronvolt) photons and the presence of very-high-energy (more than 100 gigaelectronvolts) emission have remained elusive(4). Here we report observations of very-high-energy emission in the bright GRB 180720B deep in the GRB afterglow-ten hours after the end of the prompt emission phase, when the X-ray flux had already decayed by four orders of magnitude. Two possible explanations exist for the observed radiation: inverse Compton emission and synchrotron emission of ultrarelativistic electrons. Our observations show that the energy fluxes in the X-ray and gamma-ray range and their photon indices remain comparable to each other throughout the afterglow. This discovery places distinct constraints on the GRB environment for both emission mechanisms, with the inverse Compton explanation alleviating the particle energy requirements for the emission observed at late times. The late timing of this detection has consequences for the future observations of GRBs at the highest energies.
  • Abdalla, H., et al. (författare)
  • Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE gamma-ray observations with HESS
  • 2019
  • Ingår i: Astronomy and Astrophysics. - EDP Sciences. - 0004-6361. ; 627, s. 1-19
  • Tidskriftsartikel (refereegranskat)abstract
    • The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100MeV &lt; E &lt; 100 GeV) gamma-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E &gt; 100 GeV) gamma-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8 : 7 sigma significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 +/- 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r greater than or similar to 1 : 7 X 1017 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.
  • Abdalla, H., et al. (författare)
  • First ground-based measurement of sub-20 GeV to 100 GeV gamma-Rays from the Vela pulsar with HESS II
  • 2018
  • Ingår i: Astronomy and Astrophysics. - EDP Sciences. - 0004-6361. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We report on the measurement and investigation of pulsed high-energy y-ray emission from the Vela pulsar, PSR B0833-45, based on observations with the largest telescope of H.E.S.S., CT5, in monoscopic mode, and on data obtained with the Fermi-LAT. Methods. Data from 40.3 h of observations carried out with the H.E.S.S. II array from 2013 to 2015 have been used. A dedicated very low-threshold event reconstruction and analysis pipeline was developed to achieve the lowest possible energy threshold. Eight years of Fermi-LAT data were analysed and also used as reference to validate the CT5 telescope response model and analysis methods. Results. A pulsed gamma-ray signal at a significance level of more than 15 sigma is detected from the P2 peak of the Vela pulsar light curve. Of a total of 15 835 events, more than 6000 lie at an energy below 20 GeV, implying a significant overlap between H.E.S.S. II-CT5 and the Fermi-LAT. While the investigation of the pulsar light curve with the LAT confirms characteristics previously known up to 20 GeV in the tens of GeV energy range, CT5 data show a change in the pulse morphology of P2, i.e. an extreme sharpening of its trailing edge, together with the possible onset of a new component at 3.4 sigma significance level. Assuming a power-law model for the P2 spectrum, an excellent agreement is found for the photon indices (Gamma similar or equal to 4.1) obtained with the two telescopes above 10 GeV and an upper bound of 8% is derived on the relative offset between their energy scales. Using data from both instruments, it is shown however that the spectrum of P2 in the 10-100 GeV has a pronounced curvature; this is a confirmation of the sub-exponential cut-off form found at lower energies with the LAT. This is further supported by weak evidence of an emission above 100 GeV obtained with CT5. In contrast, converging indications are found from both CT5 and LAT data for the emergence of a hard component above 50 GeV in the leading wing (LW2) of P2, which possibly extends beyond 100 GeV. Conclusions. The detection demonstrates the performance and understanding of CT5 from 100 GeV down to the sub-20 GeV domain, i.e. unprecedented low energy for ground-based gamma-ray astronomy. The extreme sharpening of the trailing edge of the P2 peak found in the H.E.S.S. II light curve of the Vela pulsar and the possible extension beyond 100 GeV of at least one of its features, LW2, provide further constraints to models of gamma-Ray emission from pulsars.
  • Abdalla, H., et al. (författare)
  • HESS detection of very high-energy gamma-ray emission from the quasar PKS 0736+017
  • 2020
  • Ingår i: Astronomy and Astrophysics. - EDP Sciences. - 0004-6361 .- 1432-0746. ; 633, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Flat-spectrum radio-quasars (FSRQs) are rarely detected at very high energies (E&amp; x2004;&gt;=&amp; x2004;100 GeV) due to their low-frequency-peaked spectral energy distributions. At present, only six FSRQs are known to emit very high-energy (VHE) photons, representing only 7% of the VHE extragalactic catalog, which is largely dominated by high-frequency-peaked BL Lacertae objects. Aims. Following the detection of MeV-GeV gamma-ray flaring activity from the FSRQ PKS 0736+017 (z&amp; x2004;=&amp; x2004;0.189) with Fermi-LAT, the H.E.S.S. array of Cherenkov telescopes triggered target-of-opportunity (ToO) observations on February 18, 2015, with the goal of studying the gamma-ray emission in the VHE band. Methods. H.E.S.S. ToO observations were carried out during the nights of February 18, 19, 21, and 24, 2015. Together with Fermi-LAT, the multi-wavelength coverage of the flare includes Swift observations in soft X-ray and optical-UV bands, and optical monitoring (photometry and spectro-polarimetry) by the Steward Observatory, and the ATOM, the KAIT, and the ASAS-SN telescopes. Results. VHE emission from PKS 0736+017 was detected with H.E.S.S. only during the night of February 19, 2015. Fermi-LAT data indicate the presence of a gamma-ray flare, peaking at the time of the H.E.S.S. detection, with a flux doubling timescale of around six hours. The gamma-ray flare was accompanied by at least a 1 mag brightening of the non-thermal optical continuum. No simultaneous observations at longer wavelengths are available for the night of the H.E.S.S. detection. The gamma-ray observations with H.E.S.S. and Fermi-LAT are used to put constraints on the location of the gamma-ray emitting region during the flare: it is constrained to be just outside the radius of the broad-line region r(BLR) with a bulk Lorentz factor Gamma&amp; x2004;similar or equal to&amp; x2004;20, or at the level of the radius of the dusty torus r(torus) with Gamma&amp; x2004;similar or equal to&amp; x2004;60. Conclusions. PKS 0736+017 is the seventh FSRQ known to emit VHE photons, and at z&amp; x2004;=&amp; x2004;0.189 is the nearest so far. The location of the gamma-ray emitting region during the flare can be tightly constrained thanks to opacity, variability, and collimation arguments.
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