51. Sensitivity projections for dark matter searches with the Fermi large area telescopeGabrijela Zaharijas, Collaboration Fermi LAT, 2016, izvirni znanstveni članek Opis: 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.
Ključne besede: dark matter, gamma rays
Objavljeno v RUNG: 20.06.2016; Ogledov: 4630; Prenosov: 0
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52. Constraints on the Galactic Dark Matter signal from the Fermi-LAT measurement of the diffuse gamma-ray emissionGabrijela Zaharijas, 2012, objavljeni znanstveni prispevek na konferenci Opis: We study diffuse gamma-ray emission at intermediate Galactic latitudes measured by the Fermi Large Area Telescope with the aim of searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We set both, conservative dark matter limits requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission and limits derived based on modeling the foreground astrophysical diffuse emission. Uncertainties in several parameters which characterize conventional astrophysical emission are taken into account using a profile likelihood formalism. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.
Ključne besede: gamma rays, Galactic diffuse emission, dark matter serach
Objavljeno v RUNG: 03.05.2016; Ogledov: 4398; Prenosov: 0
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55. Galactic Dark Matter signal and the Fermi-LAT measurement of the diffuse gamma-ray emissionGabrijela Zaharijas, objavljeni znanstveni prispevek na konferenci Opis: We study diffuse gamma-ray emission at intermediate Galactic latitudes measured by the Fermi LAT with the aim of searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We present and improve upon conservative dark matter limits obtained with no modeling of the foreground astrophysical diffuse emission. We do so, by taking into account uncertainties in several parameters which characterize conventional astrophysical emission and using a profile likelihood formalism. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.
Ključne besede: Dark matter, high-energy gamma rays
Objavljeno v RUNG: 21.03.2016; Ogledov: 4453; Prenosov: 0
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56. Prospects On Testing Lorentz Invariance Violation With The Cherenkov Telescope ArrayM. K. Daniel, Andrej Filipčič, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, 2015, objavljeni znanstveni prispevek na konferenci Ključne besede: Cherenkov Telescope Array (CTA), Lorentz Invariance Violation (LIV), Very High Energy (VHE) gamma-rays, fundamental physics probes, Active Galactic Nuclei (AGN), Gamma Ray Bursts (GRBs), pulsars
Objavljeno v RUNG: 14.03.2016; Ogledov: 4584; Prenosov: 221
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57. FERMI-LAT OBSERVATIONS OF HIGH-ENERGY γ-RAY EMISSION TOWARD THE GALACTIC CENTERGabrijela Zaharijas, B. L. Winer, 2016, izvirni znanstveni članek Opis: The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1–100 GeV from a 15° × 15° region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the γ-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ∼1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15° × 15° region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.
Ključne besede: cosmic rays – Galaxy: center – gamma-rays: general – gamma-rays: ISM – radiation mechanisms: non-thermal
Objavljeno v RUNG: 02.03.2016; Ogledov: 5204; Prenosov: 290
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58. 2FHL : THE SECOND CATALOG OF HARD FERMI-LAT SOURCESM. Ackermann, Gabrijela Zaharijas, Collaboration Fermi LAT, 2016, izvirni znanstveni članek Opis: We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2 TeV energy range. In this energy band, Fermi-LAT has detected 360 sources, which constitute the second catalog of hard Fermi-LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (∼1 7 radius at 68% C.L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi-LATon orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.
Ključne besede: catalogs – gamma-rays
Objavljeno v RUNG: 25.02.2016; Ogledov: 5190; Prenosov: 0
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