Search for Galactic dark matter substructures with Cherenkov telescopes

Weakly interacting massive dark matter (DM) particles are expected to self-annihilate or decay, generating high-energy photons in these processes. This establishes the possibility for indirect detection of DM by \gamma-ray telescopes. For probing the secondary products of DM, accurate knowledge about the DM density distribution in potential astrophysical targets is crucial. In this contribution, the prospects for the detection of subhalos in the Galactic DM halo with present and future imaging atmospheric Cherenkov telescopes (IACT) are investigated. The source count distribution and angular power spectra for \gamma-rays originating from annihilating DM in subhalos are calculated from N-body simulation results. To study the systematic uncertainties coming from the modeling of the DM density distribution, parameters describing the \gamma-ray yield from subhalos are varied in 16 benchmark models. We conclude that Galactic subhalos of annihilating DM are probably too faint to be a promising target for IACT observations, even with the prospective Cherenkov Telescope Array (CTA).Comment: 8 pages, 5 figures. Included in Proceedings of the 34th International Cosmic Ray Conference, The Hague, The Netherlands (July 30 - August 6, 2015

Dark matter substructure modelling and sensitivity of the Cherenkov Telescope Array to Galactic dark halos

Hierarchical structure formation leads to a clumpy distribution of dark matter in the Milky Way. These clumps are possible targets to search for dark matter annihilation with present and future $\gamma$-ray instruments. Many uncertainties exist on the clump distribution, leading to disputed conclusions about the expected number of detectable clumps and the ensuing limits that can be obtained from non-detection. In this paper, we use the CLUMPY code to simulate thousands of skymaps for several clump distributions. This allows us to statistically assess the typical properties (mass, distance, angular size, luminosity) of the detectable clumps. Varying parameters of the clump distributions allows us to identify the key quantities to which the number of detectable clumps is the most sensitive. Focusing our analysis on two extreme clump configurations, yet consistent with results from numerical simulations, we revisit and compare various calculations made for the Fermi-LAT instrument, in terms of number of dark clumps expected and the angular power spectrum for the Galactic signal. We then focus on the prospects of detecting dark clumps with the future CTA instrument, for which we make a detailed sensitivity analysis using open-source CTA software. Based on a realistic scenario for the foreseen CTA extragalactic survey, and accounting for a post-trial sensitivity in the survey, we show that we obtain competitive and complementary limits to those based on long observation of a single bright dwarf spheroidal galaxy.Comment: 29 pages + appendix, 15 figures. V2: Sects. 3.3, 4, and 5.3 extended, results unchanged (matching accepted JCAP version

No more cakes and ale: banks and banking regulation in the post-bretton woods macro-regime

There is a broad consensus that financialization has brought many disadvantages and few benefits. This raises a simple question: How did it come about? Why did professional observers allow it to happen even though financialization was not a hidden process? Can we identify sources of legitimation for financialization? To limit the scope of our analysis, we focus on the role of banks to answer these questions. We study changing expectations towards banks from a transdisciplinary perspective, using insights from macroeconomics, sociology and political science. We find that the legitimation of financialization has been multi-faceted. However, at many crucial junctures, the perceived but doubtful need to “increase competition” for banks has tipped the scale in favor of the policies underlying it. The disciplining effects of competition though, have not resulted in less cakes and ale for banks

High energy astroparticle physics for high school students

The questions about the origin and type of cosmic particles are not only fascinating for scientists in astrophysics, but also for young enthusiastic high school students. To familiarize them with research in astroparticle physics, the Pierre Auger Collaboration agreed to make 1% of its data publicly available. The Pierre Auger Observatory investigates cosmic rays at the highest energies and consists of more than 1600 water Cherenkov detectors, located near Malarg\"{u}e, Argentina. With publicly available data from the experiment, students can perform their own hands-on analysis. In the framework of a so-called Astroparticle Masterclass organized alongside the context of the German outreach network Netzwerk Teilchenwelt, students get a valuable insight into cosmic ray physics and scientific research concepts. We present the project and experiences with students.Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands, PoS(ICRC2015)30

MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study

https://pos.sissa.it/395/815/pdfPublished versio

Prospects for Galactic dark matter searches with the Cherenkov Telescope Array (CTA)

Die vorliegende Arbeit beschreibt einen semi-analytischen Ansatz zur Modellierung der Dichteverteilung von DM im Galaktischen Halo. Aus den verschiedenen Substrukturmodellen wird die γ-Strahlungsintensität, welche die Erde erreicht, berechnet. Eine Spannbreite plausibler γ-Strahlungsintensitäten aufgrund der Paarvernichtung Galaktischer DM wird vorgeschlagen, welche die Vorhersagen verschiedener früherer Studien umfasst, und es werden die durchschnittlichen Massen, Abstände und ausgedehnten Strahlungsprofile der γ-strahlungsintensivsten DM-Verdichtungen berechnet. Schließlich werden die DM-Modelle für eine umfassende Berechnung der Nachweismöglichkeit Galaktischer Substrukturen mit CTA verwendet. Die instrumentelle Sensitivität zum Nachweis der γ-strahlungsintensivsten DM-Substruktur wird für eine mit CTA geplanten großflächigen Himmelsdurchmusterung außerhalb der Galaktischen Ebene berechnet. Die Berechnung wird mit CTA Analyse- Software und einer Methode durchgeführt, welche auf einer Likelihood beruht. Eine alternative, ebenfalls Likelihood-basierte Analysemethode wird entwickelt, mit welcher DM-Substrukturen als äumliche Anisotropien im Multipolspektrum des Datensatzes einer Himmelsdurchmusterung nachgewiesen werden können. Die Analysen ergeben, dass eine Himmelsdurchmusterung mit CTA und eine anschließende Suche nach γ-Strahlung von DM-Substrukturen Wirkungsquerschnitte für eine Paarvernichtung in der Größenordnung von (σv) > 1 × 10−24 cm3 s−1 für eine DM-Teilchenmasse von mχ ∼ 500 GeV auf einem Vertrauensniveau von 95% ausschließen kann. Diese Sensitivität ist vergleichbar mit Langzeitbeobachtungen einzelner Zwerggalaxien mit CTA. Eine modellunabhängige Analyse ergibt, dass eine Himmelsdurchmusterung mit CTA Anisotropien im diffusen γ-Strahlungshintergrund oberhalb von 100 GeV für relative Schwankungen von CPF > 10−2 nachweisen kann.In the current understanding of structure formation in the Universe, the Milky Way is embedded in a clumpy halo of dark matter (DM). Regions of high DM density are expected to emit enhanced γ-radiation from the DM relic annihilation. This γ-radiation can possibly be detected by γ-ray observatories on Earth, like the forthcoming Cherenkov Telescope Array (CTA). This dissertation presents a semi-analytical density modeling of the subclustered Milky Way DM halo, and the γ-ray intensity at Earth from DM annihilation in Galactic subclumps is calculated for various substructure models. It is shown that the modeling approach is able to reproduce the γ-ray intensities obtained from extensive dynamical DM simulations, and that it is consistent with the DM properties derived from optical observations of dwarf spheroidal galaxies. A systematic confidence margin of plausible γ-ray intensities from Galactic DM annihilation is estimated, encompassing a variety of previous findings. The average distances, masses, and extended emission profiles of the γ-ray-brightest DM clumps are calculated. The DM substructure models are then used to draw reliable predictions for detecting Galactic DM density clumps with CTA, using the most recent benchmark calculations for the performance of the instrument. A Likelihood-based calculation with CTA analysis software is applied to find the instrumental sensitivity to detect the γ-ray-brightest DM clump in the projected CTA extragalactic survey. An alternative Likelihood-based analysis method is developed, to detect DM substructures as anisotropies in the angular power spectrum of the extragalactic survey data. The analyses predict that the CTA extragalactic survey will be able to probe annihilation cross sections of ⟨σv⟩ > 1 × 10−24 cm3 s−1 at the 95% confidence level for a DM particle mass of mχ ∼ 500 GeV from DM annihilation in substructures. This sensitivity is compatible with long-term observations of single dwarf spheroidal galaxies with CTA. Independent of a particular source model, it is found that the CTA extragalactic survey will be able to detect anisotropies in the diffuse γ-ray background above 100 GeV at a relative amplitude of CP_F > 10−2

Solutions of the Einstein-Maxwell equations with quasistatic transitions to black holes

Die Majumdar-Papapetrou-Lösungsklasse der Einstein-Maxwell-Gleichungen, welche statische, extremal geladene Staubkonfigurationen beschreibt, zeigt interessante analoge Eigenschaften zu stationär rotierenden relativistischen Systemen. Jede räumlich begrenzte, reguläre Materieverteilung aus extremal geladenem Staub, welche einer entsprechenden asymptotisch flachen Majumdar-Papa-petrou-Lösung entspricht, kann in einem quasistatischen parametrischen Übergang soweit komprimiert werden, dass sie im Grenzfall als Schwarzes Loch erscheint (als sog. quasi black hole). Es wird gezeigt, dass in diesem Grenzfall die Raumzeit immer in charakteristischer Weise zerfällt. Als äußere Raumzeit entsteht die extreme Reissner-Nordström-Metrik außerhalb des Ereignishorizonts. Als innere Raumzeit liegt weiterhin eine reguläre, allerdings nicht asymptotisch flache sowie im Allgemeinen nicht kugelsymmetrische Metrik vor. Die Ergebnisse werden anhand konkreter Lösungsbeispiele der Majumdar-Papapetrou-Klasse veranschaulicht. Zudem wird die geodätische Bewegung massiver Testteilchen im Quasi-Black-Hole-Grenzfall untersucht. Die wesentlichen Ergebnisse dieser Diplomarbeit sind zusammengefasst im Artikel On the black hole limit of electrically counterpoised dust configurations, Classical and Quantum Gravity 28, 2011 (MEINEL und HÜTTEN, 2011)Majumdar-Papapetrou solutions of the Einstein-Maxwell equations describing static configurations of electrically counterpoised dust (ECD) show interesting properties similar to stationary rotating relativistic systems. Every localized regular ECD-distribution belonging to a corresponding asymptotically flat Majumdar-Papapetrou solution can, by means of a quasistatic parametric transition, be condensed to the limit of a quasi black hole state. It is shown that in this limit the original spacetime separates always in a characteristic way. As an “exterior” spacetime the extreme Reisser-Nordström metric outside the event horizon is formed. As an “interior” spacetime, a regular, but non-asymptotically flat and in general non-spherically symmetric metric is still existent. The results are illustrated by explicit examples of Majumdar-Papapetrou solutions with transitions to quasi black hole states. Also, the geodesic motion of massive test particles in the quasi black hole limit is discussed. The main results of this diploma thesis are summarized in the article “On the black hole limit of electrically counterpoised dust configurations” published at Classical and Quantum Gravity 28, 2011 (MEINEL und HÜTTEN, 2011)

γ-ray and ν Searches for Dark-Matter Subhalos in the Milky Way with a Baryonic Potential

The distribution of dark-matter (DM) subhalos in our galaxy remains disputed, leading to varying γ -ray and ν flux predictions from their annihilation or decay. In this work, we study how, in the inner galaxy, subhalo tidal disruption from the galactic baryonic potential impacts these signals. Based on state-of-the art modeling of this effect from numerical simulations and semi-analytical results, updated subhalo spatial distributions are derived and included in the CLUMPY code. The latter is used to produce a thousand realizations of the γ -ray and ν sky. Compared to predictions based on DM only, we conclude a decrease of the flux of the brightest subhalo by a factor of 2 to 7 for annihilating DM and no impact on decaying DM: the discovery prospects or limits subhalos can set on DM candidates are affected by the same factor. This study also provides probability density functions for the distance, mass, and angular distribution of the brightest subhalo, among which the mass may hint at its nature: it is most likely a dwarf spheroidal galaxy in the case of strong tidal effects from the baryonic potential, whereas it is lighter and possibly a dark halo for DM only or less pronounced tidal effects

TeV Dark Matter Searches in the Extragalactic Gamma-ray Sky

High-energetic gamma rays from astrophysical targets constitute a unique probe for annihilation or decay of heavy particle dark matter (DM). After several decades, diverse null detections have resulted in strong constraints for DM particle masses up to the TeV scale. While the gamma-ray signature is expected to be universal from various targets, uncertainties of astrophysical origin strongly affect and weaken the limits. At the same time, spurious signals may originate from non-DM related processes. The many gamma-ray targets in the extragalactic sky being searched for DM play a crucial role to keep these uncertainties under control and to ultimately achieve an unambiguous DM detection. Lately, a large progress has been made in combined analyses of TeV DM candidates towards different targets by using data from various instruments and over a wide range of gamma-ray energies. These approaches not only resulted in an optimal exploitation of existing data and an improved sensitivity, but also helped to level out target- and instrument-related uncertainties. This review gathers all searches in the extragalactic sky performed so far with the space-borne Fermi-Large Area Telescope, the ground-based imaging atmospheric Cherenkov telescopes, and the High-Altitude Water Cherenkov Gamma-Ray Observatory (HAWC). We discuss the different target classes and provide a complete list of all analyses so far