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61.
M31 gamma-ray emission - a closer look at different explanations
Christopher Eckner, Pasquale D. Serpico, Jovana Petrovic, Tijana Prodanovic, 2017, published scientific conference contribution

Keywords: Milky Way, M31, gamma-rays, millisecond pulsars, dark matter
Published in RUNG: 30.01.2018; Views: 4855; Downloads: 152
.pdf Full text (773,73 KB)

62.
Time-varying sodium absorption in the Type Ia supernova 2013gh
Raphael Ferretti, R. Amanullah, Ariel Goobar, Joel Johansson, Tanja Petrushevska, 2016, original scientific article

Abstract: Context. Temporal variability of narrow absorption lines in high-resolution spectra of Type Ia supernovae (SNe Ia) is studied to search for circumstellar matter. Time series which resolve the profiles of absorption lines such as Na I D or Ca II H&K are expected to reveal variations due to photoionisation and subsequent recombination of the gases. The presence, composition, and geometry of circumstellar matter may hint at the elusive progenitor system of SNe Ia and could also affect the observed reddening law. Aims. To date, there are few known cases of time-varying Na I D absorption in SNe Ia, all of which occurred during relatively late phases of the supernova (SN) evolution. Photoionisation, however, is predicted to occur during the early phases of SNe Ia, when the supernovae peak in the ultraviolet. We attempt, therefore, to observe early-time absorption-line variations by obtaining high-resolution spectra of SNe before maximum light. Methods. We have obtained photometry and high-resolution spectroscopy of SNe Ia 2013gh and iPTF 13dge, to search for absorptionline variations. Furthermore, we study interstellar absorption features in relation to the observed photometric colours of the SNe. Results. Both SNe display deep Na I D and Ca II H&K absorption features. Furthermore, small but significant variations are detected in a feature of the Na I D profile of SN 2013gh. The variations are consistent with either geometric effects of rapidly moving or patchy gas clouds or photoionisation of Na I gas at R ≈ 1019 cm from the explosion. Conclusions. Our analysis indicates that it is necessary to focus on early phases to detect photoionisation effects of gases in the circumstellar medium of SNe Ia. Different absorbers such as Na I and Ca II can be used to probe for matter at different distances from the SNe. The nondetection of variations during early phases makes it possible to put limits on the abundance of the species at those distances.
Keywords: supernovae: general – supernovae: individual: SN 2013gh – dust, extinction – circumstellar matter – supernovae: individual: iPTF 13dge
Published in RUNG: 23.01.2018; Views: 4340; Downloads: 0
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63.
Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 μm
Rahman Amanullah, Tanja Petrushevska, 2015, original scientific article

Abstract: We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2–2 μm. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B − V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction RV. In particular, we note that for the two SNe with E(B − V) ≳ 1 mag, for which the colour excess is dominated by dust extinction, we find RV = 1.4 ± 0.1 and RV = 2.8 ± 0.1. Adding UV photometry reduces the uncertainty of fitted RV by ∼50 per cent allowing us to also measure RV of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.
Keywords: circumstellar matter, supernovae: general, supernovae: individual: SNe 2012cg, supernovae: individual: 2012cu, dust, extinction
Published in RUNG: 23.01.2018; Views: 4296; Downloads: 0
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64.
Search for Physics beyond the Standard Model with the CRESST Experiment
2017, master's thesis

Abstract: In spite of the successes of observational astro- and particle physics and cosmology very much of the universe remains unknown. The Standard Model of particle physics is a theory describing the electromagnetic, weak, and strong nuclear interactions, as well as classifying all the subatomic particles known. But there is overwhelming evidence, that all the known particles, the ordinary (baryonic) matter, the building blocks of planets, stars and ourselves, only make up about 4.9% of the energy content of the universe. The standard model of cosmology (CDM) indicates that the total mass-energy of the universe contains beside the 4.9% ordinary matter two other components: 26.8% dark matter and 68.3% dark energy. The accelerating expansion of the Universe is the result of the effect of the dark energy with its most simple form given by a cosmological constant in Einstein's Equation. Dark matter is an unidentified type of matter that is not accounted for by dark energy and neutrinos and is generally believed to be a non-relativistic, charge neutral and non-baryonic new form of matter. Although dark matter has not been directly observed yet, its existence and properties are inferred from its gravitational effects such as the motions of visible matter, gravitational lensing, its influence on the universe's large-scale structure, and its effects in the cosmic microwave background. Thus the search for Dark Matter is the search for physics beyond the standard model. Although the nature of dark matter is yet unknown, its presence is crucial to understanding the future of the universe. The CRESST experiment is searching for direct evidence in the form of a nuclear recoil induced on a scintillating CaWO4 crystal by a dark matter particle, and is installed and taking data underground at Laboratory Nazionali del Gran Sasso (LNGS) in Italy. While both, dark energy and dark matter, have not been detected directly, a class of dark matter particles that interact only via gravity and the weak force, referred to asWeakly Interacting Massive Particles (WIMPs), has been established as the leading candidate among the dark matter community. For this thesis a special model of dark matter was studied, namely the dark photon. This thesis provides a detailed description of the calculation of the 90% upper limit on the dark photon kinetic mixing based on data from the second phase of the CRESST experiment. The analysis was carried out in a frequentist approach based on the (unbinned) maximum-likelihood method and likelihood ratios. To make a statement about the calculated result and its quality, the used algorithm had to be tested, what was done with Monte Carlo simulations (pseudo data).
Keywords: astro physics, particle physics, cosmology, universe, Standard Model of particle physics, standard model of cosmology, matter, ordinary matter, dark matter, dark energy, accelerating expansion of the Universe, non-baryonic, new form of matter, gravitational lensing, cosmic microwave background, search for physics beyond the standard model, CRESST experiment, direct detection, CaWO4 crystal, underground laboratory, Laboratory Nazionali del Gran Sasso, Weakly Interacting Massive Particles, WIMP, dark photon, 90% upper limit, upper limit, kinetic mixing, frequentist approach, unbinned, maximum likelihood
Published in RUNG: 13.10.2017; Views: 5504; Downloads: 0
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ESTIMATING THE GeV EMISSION OF MILLISECOND PULSARS IN DWARF SPHEROIDAL GALAXIES
Miles Winter, Gabrijela Zaharijas, Keith Bechtol, Justin Vandenbroucke, 2016, original scientific article

Keywords: dark matter – Local Group – pulsars: general
Published in RUNG: 28.11.2016; Views: 5381; Downloads: 0
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69.
Dark Matter search with the Fermi Large Area Telescope
Gabrijela Zaharijas, unpublished invited conference lecture

Abstract: High energy gamma-rays are one of the most promising tools to constrain or reveal the nature of dark matter. During the almost eight years of the Fermi satellite mission, the data from its Large Area Telescope (LAT) were used to set constraints on the dark matter cross section to various particle channels which now cut well into the theoretically motivated region of the parameter space. In this talk I will describe methods used to search for evidence of dark matter with the LAT, and review the status of the searches. Special attention will be given to the latest indications of the origin of the unaccounted gamma-ray excess at few GeV in the Fermi-LAT data in the region around the Galactic Center, which steered lots of attention as it was shown to be consistent with putative signals of WIMP dark matter particles. Finally I will discuss projections of the expected sensitivities with continued LAT data taking.
Keywords: dark matter, Fermi LAT experiment
Published in RUNG: 21.06.2016; Views: 5745; Downloads: 0
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70.
Sensitivity projections for dark matter searches with the Fermi large area telescope
Gabrijela Zaharijas, Collaboration Fermi LAT, 2016, original scientific article

Abstract: The nature of dark matter is a longstanding enigma of physics; it may consist of particles beyond the Standard Model that are still elusive to experiments. Among indirect searchtechniques, which look for stable products from the annihilation or decay of dark matter particles, or from axions coupling to high-energy photons, observations of the γ -ray sky have come to prominence over the last few years, because of the excellent sensitivity of the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope mission. The LAT energy range from 20 meV to above 300 GeV is particularly well suited for searching for products of the interactions of dark matter particles. In this report we describe methods used to search for evidence of dark matter with the LAT, and review the status of searches performed with up to six years of LAT data. We also discuss the factors that determine the sensitivities of these searches, including the magnitudes of the signals and the relevant backgrounds, considering both statistical and systematic uncertainties. We project the expected sensitivities of each search method for 10 and 15 years of LAT data taking. In particular, we find that the sensitivity of searches targeting dwarf galaxies, which provide the best limits currently, will improve faster than the square root of observing time. Current LAT limits for dwarf galaxies using six years of data reach the thermal relic level for masses up to 120 GeV for the bb ̄ annihilation channel for reasonable dark matter density profiles. With projected discoveries of additional dwarfs, these limits could extend to about 250 GeV. With as much as 15 years of LAT data these searches would be sensitive to dark matter annihilations at the thermal relic cross section for masses to greater than 400 GeV (200 GeV) in the bb ̄(τ+τ−) annihilation channels.
Keywords: dark matter, gamma rays
Published in RUNG: 20.06.2016; Views: 5513; Downloads: 0
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