Suche nach dunkler Materie mit den H.E.S.S.-Cherenkov-Teleskopen

Die Natur der dunklen Materie ist nach wie vor ungeklart und stellt eine der fundamentalsten Fragen der aktuellen Kosmologie dar. In vielen verschiedenen Experimenten wird versucht, diese Teilchen, die sogenannten WIMPs (aus dem Englischen: Weakly Interacting Massive Particles), nachzuweisen. In einigen Modellen der dunklen Materie wird vorhergesagt, dass sehr hochenergetische -Strahlung durch Annihilation der WIMPs in konzentrierten Ansammlungen dunkler Materie produziert wird. Im Rahmen der vorliegenden Arbeit wurden anhand von Beobachtungen im Energiebereich von 100 GeV bis 100 TeV mit dem System abbildender Cherenkov-Teleskope des H.E.S.S.-Experiments (aus dem Englischen: High Energy Stereoscopic System) verschiedene Objekte untersucht, ob die gemessene Strahlung ihren Ursprung in der Annihilation von Teilchen dunkler Materie haben konnte. Das Zentrum unserer Galaxie ist ein in der Literatur viel diskutierter Bereich, in dem sehr hochenergetische -Strahlung aus Annihilation dunkler Materie entstehen konnte. Es wurde mit H.E.S.S. sehr hochenergetische -Strahlung aus dieser Richtung nachgewiesen. Es wird aber gezeigt, dass die gemessene Strahlung aus der Richtung des galaktischen Zentrums nicht ausschlie lich von dunkler Materie erzeugt wird. Daher wurde zusatzlich untersucht, welche Aussagen mit der Hypothese getro en werden konnen, dass nur ein Anteil aus dieser Strahlung besteht. Es konnten interessante Einschrankungen auf das Dichtepro l der hypothetischen DM-Ansammlung gewonnen werden; ein Dichtepro l nach Moore kann fur viele Parametersatze der untersuchten Modelle ausgeschlossen werden. Auf den Wirkungsquerschnitt der Annihilation kann keine relevante Einschrankung erzielt werden..thesi

Time-dependent absorption of very high-energy gamma-rays from the Galactic center by pair-production

Very high energy (VHE) gamma-rays have been detected from the direction of the Galactic center. The H.E.S.S. Cherenkov telescopes have located this gamma-ray source with a preliminary position uncertainty of 8.5" per axis (6" statistic + 6" sytematic per axis). Within the uncertainty region several possible counterpart candidates exist: the Super Massive Black Hole Sgr A*, the Pulsar Wind Nebula candidate G359.95-0.04, the Low Mass X-Ray Binary-system J174540.0-290031, the stellar cluster IRS 13, as well as self-annihilating dark matter. It is experimentally very challenging to further improve the positional accuracy in this energy range and therefore, it may not be possible to clearly associate one of the counterpart candidates with the VHE-source. Here, we present a new method to investigate a possible link of the VHE-source with the near environment of Sgr A* (within approximately 1000 Schwarzschild radii). This method uses the time- and energy-dependent effect of absorption of gamma-rays by pair-production (in the following named pair-eclipse) with low-energy photons of stars closely orbiting the SMBH Sgr A*.Comment: 4 pages, 6 figures, Published in Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy (Gamma 08), Heidelber

Implications for constrained supersymmetry of combined H.E.S.S. observations of dwarf galaxies, the Galactic halo and the Galactic Centre

In order to place limits on dark matter (DM) properties using $\gamma$-ray observations, previous analyses have often assumed a very simple parametrisation of the $\gamma$-ray annihilation yield; typically, it has been assumed that annihilation proceeds through a single channel only. In realistic DM models, annihilation may occur into many different final states, making this quite a rough ansatz. With additional processes like virtual internal bremsstrahlung and final state radiation, this ansatz becomes even more incorrect, and the need for scans of explicit model parameter spaces becomes clear. Here we present scans of the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM), considering $\gamma$-ray spectra from three dwarf galaxies, the Galactic Centre region and the broader Galactic halo, as obtained with the High-Energy Stereoscopic System (H.E.S.S.). We present a series of likelihood scans combining the H.E.S.S. data with other experimental results. We show that observations of the Sagittarius, Carina and Sculptor dwarf galaxies disfavour the coannihilation region of the CMSSM and models with large annihilation cross-sections. This is true even under reasonable assumptions about the DM density profiles, and constitutes the strongest constraint to date on coannihilation models within the CMSSM. The Galactic halo has a similar, but weaker, effect. The Galactic Centre search is complicated by a strong (unknown) $\gamma$-ray source, and we see no effect on the CMSSM parameter space when assuming a realistic Galactic Centre DM density profile.Comment: 18 pages, 10 figures Major changes: added H.E.S.S. results on halo and two additional dwarf galaxies, title, abstract and text changed accordingl

A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices $(0.7 < \Gamma <1.4)$ and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices $(1.0 < \Gamma < 1.7)$, however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. The observation of high-energy gamma-ray emission from a globular cluster thus provides a reliable independent method to assess their millisecond pulsar populations that can be used to make constraints on the original neutron star X-ray binary population, essential for understanding the importance of binary systems in slowing the inevitable core collapse of globular clusters.Comment: Accepted for publication in A&A. Corresponding authors: J. Kn\"odlseder, N. Webb, B. Pancraz

Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe

The Extragalactic Background Light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts (GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for these sources, we investigate the effect of gamma-ray flux attenuation by the EBL. We place upper limits on the gamma-ray opacity of the Universe at various energies and redshifts, and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. (2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A. Reimer, L.C. Reye

Addendum - GAMBIT: the global and modular beyond-the-standard-model inference tool

In Ref. (GAMBIT Collaboration: Athron et. al., Eur. Phys. J. C. arXiv:1705.07908, 2017) we introduced the global-fitting framework GAMBIT. In this addendum, we describe a new minor version increment of this package. GAMBIT 1.1 includes full support for Mathematica backends, which we describe in some detail here. As an example, we backend SUSYHD (Vega and Villadoro, JHEP 07:159, 2015), which calculates the mass of the Higgs boson in the MSSM from effective field theory. We also describe updated likelihoods in PrecisionBit and DarkBit, and updated decay data included in DecayBit

GAMBIT: the global and modular beyond-the-standard-model inference tool

Abstract In Ref. (GAMBIT Collaboration: Athron et. al., Eur. Phys. J. C. arXiv:1705.07908, 2017) we introduced the global-fitting framework GAMBIT. In this addendum, we describe a new minor version increment of this package. GAMBIT 1.1 includes full support for Mathematica backends, which we describe in some detail here. As an example, we backend SUSYHD  (Vega and Villadoro, JHEP 07:159, 2015), which calculates the mass of the Higgs boson in the MSSM from effective field theory. We also describe updated likelihoods in PrecisionBit and DarkBit, and updated decay data included in DecayBit