Refine
Year of publication
Document Type
- Article (42)
- Monograph/Edited Volume (5)
- Postprint (4)
- Part of Periodical (3)
- Other (2)
Keywords
- radiation mechanisms: non-thermal (11)
- galaxies: active (8)
- gamma rays: galaxies (6)
- ISM: supernova remnants (5)
- gamma rays: general (5)
- acceleration of particles (4)
- cosmic rays (4)
- BL Lacertae objects: individual: PKS 2155-304 (3)
- ISM: clouds (3)
- galaxies: jets (3)
- gamma rays: ISM (3)
- BL Lacertae objects: general (2)
- Cost-effectiveness (2)
- Cross-sectoral care (2)
- Delirium prevention (2)
- Dementia (2)
- Elective surgery (2)
- ISM: individual objects: G338.3-0.0 (2)
- Mars (2)
- Older patients (2)
- Postoperative cognitive dysfunction (2)
- Quality of life (2)
- dual GLP-1/glucagon receptor agonist (2)
- errata, addenda (2)
- exendin-4 (2)
- galaxies: nuclei (2)
- gamma rays: stars (2)
- gamma-rays: galaxies (2)
- light scattering (2)
- lipidation (2)
- molecular architecture (2)
- self-assembly (2)
- Air-pollution (1)
- Anthropogenic sources (1)
- BL Lacertae objects: individual (Mrk 501) (1)
- BL Lacertae objects: individual (PG 1553+113) (1)
- BL Lacertae objects: individual: AP Librae (1)
- BL Lacertae objects: individual: lES 0229+200 (1)
- BL Lacertae objects: individual: lES 1101-232 (1)
- Datenschutz (1)
- Digitalisierung (1)
- Eurasian Dry Grassland Group (EDGG) (1)
- European Vegetation Archive (EVA) (1)
- GrassPlot (1)
- Hochschulentwicklung (1)
- ISM: individual objects (RX J1713.7-3946, G347.3-0.5) (1)
- ISM: individual objects (SNR G338.3-0.0, SNR G338.5+0.1) (1)
- ISM: individual objects: Puppis A (1)
- Identity Management (1)
- Identitätsmanagement (1)
- Innovation (1)
- Interdisziplinarität (1)
- Lerntheorie (1)
- Methane (1)
- Methanogens (1)
- Model-driven SOA Security (1)
- Modell-getriebene SOA-Sicherheit (1)
- NO2 (1)
- Patholinguistik (1)
- Praxisbeispiele (1)
- Privacy (1)
- Qualität in Lehre und Studium (1)
- SOA Security (1)
- SOA Sicherheit (1)
- Secure Digital Identities (1)
- Secure Enterprise SOA (1)
- Sichere Digitale Identitäten (1)
- Sprachtherapie (1)
- Student-Life-Cycle (1)
- Sub-zero temperature (Celsius) (1)
- Teamwork (1)
- Tropospheric nitrogen-dioxide (1)
- Trust Management (1)
- Unternehmen (1)
- Validation (1)
- Wavelength modulation spectroscopy (laser spectroscopy) (1)
- Wissenschaftstransfer (1)
- Wortabruf (1)
- Wortfindungsstörungen (1)
- X-rays: binaries (1)
- acute encephalopathy (1)
- anticholinergic (1)
- aridity (1)
- biodiversity (1)
- biodiversity change (1)
- biomarker (1)
- black hole physics (1)
- climate change (1)
- cosmic background radiation (1)
- dark matter detectors (1)
- dark matter experiments (1)
- delirium (1)
- disturbance regime (1)
- dwarfs galaxies (1)
- forestREplot (1)
- galaxies: distances and redshifts (1)
- galaxies: individual (M 87) (1)
- galaxies: magnetic fields (1)
- gamma ray detectors (1)
- gamma-ray burst: individual (GRB 170817A) (1)
- geriatric (1)
- grassland vegetation (1)
- gravitational waves (1)
- habitat (1)
- herbaceous layer (1)
- infrared: diffuse background (1)
- intergalactic medium (1)
- lexical-semantic processing (1)
- lexikalisch-semantische Verarbeitung (1)
- macroecology (1)
- management intensity (1)
- microbial activity (1)
- multi-taxon (1)
- nested plot (1)
- nitrogen deposition (1)
- opacity (1)
- patholinguistics (1)
- plant functional traits (1)
- postoperative (1)
- quasars: individual: 3C 279 (1)
- relativistic processes (1)
- sPlot (1)
- scale-dependence (1)
- species-area relationship (SAR) (1)
- speech/language therapy (1)
- stars: early-type (1)
- stars: individual: 1FGL J1018.6-5856 (1)
- surgery (1)
- time lag (1)
- vegetation resurvey (1)
- vegetation-plot database (1)
- word retrieval (1)
- word-finding difficulties (1)
Institute
- Institut für Physik und Astronomie (30)
- Institut für Biochemie und Biologie (6)
- Institut für Geowissenschaften (3)
- Wirtschaftswissenschaften (3)
- Department Sport- und Gesundheitswissenschaften (2)
- Historisches Institut (2)
- Institut für Chemie (2)
- Strukturbereich Kognitionswissenschaften (2)
- Department Erziehungswissenschaft (1)
- Department Linguistik (1)
The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using gamma-ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant gamma-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section <sigma nu >. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach <sigma nu > values of 6 x 10(-26) cm(3) s(-1) in the W+W- channel for a DM particle mass of 1.5 TeV, and 2 x 10(-26) cm(3) s(-1) in the tau(+)tau(-) channel for a 1 TeV mass. For the first time, ground-based gamma-ray observations have reached sufficient sensitivity to probe <sigma nu > values expected from the thermal relic density for TeV DM particles.
An annihilation signal of dark matter is searched for from the central region of the Milky Way. Data acquired in dedicated on-off observations of the Galactic center region with H.E.S.S. are analyzed for this purpose. No significant signal is found in a total of similar to 9 h of on-off observations. Upper limits on the velocity averaged cross section, <sigma upsilon >, for the annihilation of dark matter particles with masses in the range of similar to 300 GeV to similar to 10 TeV are derived. In contrast to previous constraints derived from observations of the Galactic center region, the constraints that are derived here apply also under the assumption of a central core of constant dark matter density around the center of the Galaxy. Values of <sigma upsilon > that are larger than 3 x 10(-24) cm(3)/s are excluded for dark matter particles with masses between similar to 1 and similar to 4 TeV at 95% C.L. if the radius of the central dark matter density core does not exceed 500 pc. This is the strongest constraint that is derived on <sigma upsilon > for annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region.
Diffuse gamma-ray emission is the most prominent observable signature of celestial cosmic-ray interactions at high energies. While already being investigated at GeVenergies over several decades, assessments of diffuse gamma-ray emission at TeVenergies remain sparse. After completion of the systematic survey of the inner Galaxy, the H.E.S.S. experiment is in a prime position to observe large-scale diffuse emission at TeVenergies. Data of the H.E.S.S. Galactic Plane Survey are investigated in regions off known gamma-ray sources. Corresponding gamma-ray flux measurements were made over an extensive grid of celestial locations. Longitudinal and latitudinal profiles of the observed gamma-ray fluxes show characteristic excess emission not attributable to known gamma-ray sources. For the first time large-scale gamma-ray emission along the Galactic plane using imaging atmospheric Cherenkov telescopes has been observed. While the background subtraction technique limits the ability to recover modest variation on the scale of the H.E.S.S. field of view or larger, which is characteristic of the inverse Compton scatter-induced Galactic diffuse emission, contributions of neutral pion decay as well as emission from unresolved gamma-ray sources can be recovered in the observed signal to a large fraction. Calculations show that the minimum gamma-ray emission from pi(0) decay represents a significant contribution to the total signal. This detection is interpreted as a mix of diffuse Galactic gamma-ray emission and unresolved sources.
Context. Puppis A is an interesting similar to 4 kyr-old supernova remnant (SNR) that shows strong evidence of interaction between the forward shock and a molecular cloud. It has been studied in detail from radio frequencies to high-energy (HE, 0.1-100 GeV) gamma-rays. An analysis of the Fermi-LAT data has shown extended HE gamma-ray emission with a 0.2-100 GeV spectrum exhibiting no significant deviation from a power law, unlike most of the GeV-emitting SNRs known to be interacting with molecular clouds. This makes it a promising target for imaging atmospheric Cherenkov telescopes (IACTs) to probe the gamma-ray emission above 100 GeV.
Aims. Very-high-energy (VHE, E >= 0.1 TeV) gamma-ray emission from Puppis A has been, for the first time, searched for with the High Energy Stereoscopic System (HESS.).
Methods. Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the direction and energy of the incident gamma-rays in order to produce sky images and source spectra. The profile likelihood method is applied to find constraints on the existence of a potential break or cutoff in the photon spectrum.
Results. The analysis of the HESS. data does not reveal any significant emission towards Puppis A. The derived upper limits on the differential photon flux imply that its broadband gamma-ray spectrum must exhibit a spectral break or cutoff. By combining Fermi-LAT and HESS. measurements, the 99% confidence-level upper limits on such a cutoff are found to be 450 and 280 GeV, assuming a power law with a simple exponential and a sub-exponential cutoff, respectively. It is concluded that none of the standard limitations (age, size, radiative losses) on the particle acceleration mechanism, assumed to be continuing at present, can explain the lack of VHE signal. The scenario in which particle acceleration has ceased some time ago is considered as an alternative explanation. The HE/VHE spectrum of Puppis A could then exhibit a break of non-radiative origin (as observed in several other interacting SNRs, albeit at somewhat higher energies), owing to the interaction with dense and neutral material, in particular towards the NE region.
A search for dark matter linelike signals iss performed in the vicinity of the Galactic Center by the H.E.S.S. experiment on observational data taken in 2014. An unbinned likelihood analysis iss developed to improve the sensitivity to linelike signals. The upgraded analysis along with newer data extend the energy coverage of the previous measurement down to 100 GeV. The 18 h of data collected with the H.E.S.S. array allow one to rule out at 95% C.L. the presence of a 130 GeV line (at l = -1.5 degrees, b = 0 degrees and for a dark matter profile centered at this location) previously reported in Fermi-LAT data. This new analysis overlaps significantly in energy with previous Fermi-LAT and H.E.S.S. results. No significant excess associated with dark matter annihilations was found in the energy range of 100 GeV to 2 TeV and upper limits on the gamma-ray flux and the velocity weighted annihilation cross section are derived adopting an Einasto dark matter halo profile. Expected limits for present and future large statistics H.E.S.S. observations are also given.
The results of follow-up observations of the TeV gamma-ray source HESS J1640-465 from 2004 to 2011 with the High Energy Stereoscopic System (HESS) are reported in this work. The spectrum is well described by an exponential cut-off power law with photon index Gamma = 2.11 +/- 0.09(stat) +/- 0.10(sys), and a cut-off energy of E-2 = 6.0(-1.2)(+2.0) TeV. The TeV emission is significantly extended and overlaps with the northwestern part of the shell of the SNR G338.3-0.0. The new HESS results, a re-analysis of archival XMM-Newton data and multiwavelength observations suggest that a significant part of the gamma-ray emission from HESS J1640-465 originates in the supernova remnant shell. In a hadronic scenario, as suggested by the smooth connection of the GeV and TeV spectra, the product of total proton energy and mean target density could be as high as W(p)n(H) similar to 4 x 10(52)(d/10kpc)(2) erg cm(-3).
Measurement of the EBL spectral energy distribution using the VHE gamma-ray spectra of HESS blazars
(2017)
Very high-energy gamma rays (VHE, E greater than or similar to 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the Universe to VHE gamma rays is then directly related to the spectral energy distribution (SED) of the EBL. The observation of features in the VHE energy spectra of extragalactic sources allows the EBL to be measured, which otherwise is very difficult. An EBL model-independent measurement of the EBL SED with the H.E.S.S. array of Cherenkov telescopes is presented. It was obtained by extracting the EBL absorption signal from the reanalysis of high-quality spectra of blazars. From H.E.S.S. data alone the EBL signature is detected at a significance of 9.5 sigma, and the intensity of the EBL obtained in different spectral bands is presented together with the associated gamma-ray horizon.
We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a ground-based pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system.
This Letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of phi(E > 1TeV) = (3.64 +/- 0.44(stat)+/- 0.73(sys)) x 10(-13) cm(-2) s(-1), corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Gamma = 2.07 +/- 0.11(stat)+/- 0.20(sys). It is a point-like source, although an extension up to a Gaussian width of sigma = 3 arcmin cannot be discounted due to uncertainties in the H.E.S.S. point-spread function. The VHE gamma-ray flux of HESS J1641-463 is found to be constant over the observed period when checking time binnings from the year-by-year to the 28 minute exposure timescales. HESS J1641-463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association; however, Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE gamma-ray production scenarios are discussed. If the emission from HESS J1641-463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend close to 1 PeV. This object may represent a source population contributing significantly to the galactic cosmic ray flux around the knee.