Repozitorij Univerze v Novi Gorici

Iskanje po repozitoriju
A+ | A- | Pomoč | SLO | ENG

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju

Opcije:
  Ponastavi


161 - 170 / 337
Na začetekNa prejšnjo stran13141516171819202122Na naslednjo stranNa konec
161.
On velocity-dependent dark matter annihilations in dwarf satellites
Mihael Petač, Piero Ullio, Mauro Valli, 2018, izvirni znanstveni članek

Opis: Milky Way dwarf spheroidal satellites are a prime target for Dark Matter (DM) indirect searches. There have been recent reassessments of the expected DM gamma-ray signals in case of long-range interactions, commonly known as Sommerfeld enhancement. Since details of the underlying DM phase-space distribution function become critical, there are potentially large uncertainties in the final result. We provide here a first attempt towards a comprehensive investigation of these systematics, addressing the impact on the expected DM flux from Milky Way dwarfs via Bayesian inference on the available stellar kinematic datasets. After reconsidering the study case of ergodic systems, we investigate for the first time scenarios where DM particle orbits may have a radial or tangential bias. We consider both cuspy and cored parametric DM density profiles, together with the case of a non-parametric halo modelling directly connected to line-of-sight observable quantities. The main findings of our work highlight the relevance of the assumed phase-space distribution: Referring to a generalized J-factor, namely the line-of-sight convolution of the spatial part in case of velocity-dependent annihilation rate, an enhancement (suppression) with respect to the limit of isotropic phase-space distributions is obtained for the case of tangentially (radially) biased DM particle orbits. We provide new estimates for J-factors for the eight brightest Milky Way dwarfs also in the limit of velocity-independent DM annihilation, in good agreement with previous results in literature, and derive data-driven lower-bounds based on the non-parametric modelling of the halo density. The outcome of our broad study stands out as a representative of the state-of-the-art in the field, and falls within the interest of current and future experimental collaborations involved in DM indirect detection programs.
Ključne besede: dark matter, indirect detection, dwarf satellites, sommerfeld enhancement, gamma-rays
Objavljeno v RUNG: 01.10.2021; Ogledov: 1558; Prenosov: 43  (1 glas)
URL Povezava na celotno besedilo
Gradivo ima več datotek! Več...

162.
FR-0 jetted active galaxies : extending the zoo of candidate sites for UHECR acceleration
Lukas Merten, Margot Boughelilba, Anita Reimer, Paolo Da Vela, Serguei Vorobiov, Fabrizio Tavecchio, Giacomo Bonnoli, Jon Paul Lundquist, Chiara Righi, 2021, objavljeni znanstveni prispevek na konferenci

Opis: Fanaroff-Riley (FR) 0 radio galaxies form a low-luminosity extension to the well-established ultra-high-energy cosmic-ray (UHECR) candidate accelerators FR-1 and FR-2 galaxies. Their much higher number density — up to a factor five times more numerous than FR-1 with z ≤ 0.05 — makes them good candidate sources for an isotropic contribution to the observed UHECR flux. Here, the acceleration and survival of UHECR in prevailing conditions of the FR-0 environment are discussed. First, an average spectral energy distribution (SED) is compiled based on the FR0CAT. These photon fields, composed of a jet and a host galaxy component, form a minimal target photon field for the UHECR, which will suffer from electromagnetic pair production, photo-disintegration, photo-meson production losses, and synchrotron radiation. The two most promising acceleration scenarios based on Fermi-I order and gradual shear acceleration are discussed as well as different escape scenarios. When an efficient acceleration mechanism precedes gradual shear acceleration, e.g., Fermi-I orothers, FR-0 galaxies are likely UHECR accelerators. Gradual shear acceleration requires a jet Lorentz factor of Gamma>1.6, to be faster than the corresponding escape. In less optimistic models, a contribution to the cosmic-ray flux between the knee and ankle is expected to be relatively independent of the realized turbulence and acceleration.
Ključne besede: jetted active galaxies, FR-0 radiogalaxies, ultra-high energy cosmic rays, cosmic ray acceleration, cosmic ray energy losses
Objavljeno v RUNG: 16.08.2021; Ogledov: 1851; Prenosov: 3
.pdf Celotno besedilo (1,13 MB)

163.
Extrapolating FR-0 radio galaxy source properties from propagation of multi-messenger ultra-high energy cosmic rays
Jon Paul Lundquist, Lukas Merten, Serguei Vorobiov, Margot Boughelilba, Anita Reimer, Paolo Da Vela, Fabrizio Tavecchio, Giacomo Bonnoli, Chiara Righi, 2021, objavljeni znanstveni prispevek na konferenci

Opis: Recently, it has been shown that relatively low luminosity Fanaroff-Riley type 0 (FR-0) radio galaxies are a good candidate source class for a predominant fraction of cosmic rays (CR) accelerated to ultra-high energies (UHE, E>10[sup]18 eV). FR-0s can potentially provide a significant fraction of the UHECR energy density as they are much more numerous in the local universe than more energetic radio galaxies such as FR-1s or FR-2s (up to a factor of ∼5 with z≤0.05 compared to FR-1s). In the present work, UHECR mass composition and energy spectra at the FR-0 sources are estimated by fitting simulation results to the published Pierre Auger Observatory data. This fitting is done using a simulated isotropic sky distribution extrapolated from the measured FR-0 galaxy properties and propagating CRs in plausible extragalactic magnetic field configurations using the CRPropa3 framework. In addition, we present estimates of the fluxes of secondary photons and neutrinos created in UHECR interactions with cosmic photon backgrounds during CR propagation. With this approach, we aim to investigate the properties of the sources with the help of observational multi-messenger data.
Ključne besede: jetted active galaxies, FR-0 radiogalaxies, ultra-high energy cosmic rays, extragalactic magnetic fields, UHECR propagation, UHECR interactions, cosmogenic photons, cosmogenic neutrinos
Objavljeno v RUNG: 16.08.2021; Ogledov: 1847; Prenosov: 3
.pdf Celotno besedilo (2,04 MB)

164.
165.
166.
Calibration of the underground muon detector of the Pierre Auger Observatory
A. Aab, Andrej Filipčič, Jon Paul Lundquist, Samo Stanič, Marta Trini, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2021, izvirni znanstveni članek

Opis: To obtain direct measurements of the muon content of extensive air showers with energy above 10[sup]16.5 eV, the Pierre Auger Observatory is currently being equipped with an underground muon detector (UMD), consisting of 219 10 m[sup]2-modules, each segmented into 64 scintillators coupled to silicon photomultipliers (SiPMs). Direct access to the shower muon content allows for the study of both of the composition of primary cosmic rays and of high-energy hadronic interactions in the forward direction. As the muon density can vary between tens of muons per m[sup]2 close to the intersection of the shower axis with the ground to much less than one per m[sup]2 when far away, the necessary broad dynamic range is achieved by the simultaneous implementation of two acquisition modes in the read-out electronics: the binary mode, tuned to count single muons, and the ADC mode, suited to measure a high number of them. In this work, we present the end-to-end calibration of the muon detector modules: first, the SiPMs are calibrated by means of the binary channel, and then, the ADC channel is calibrated using atmospheric muons, detected in parallel to the shower data acquisition. The laboratory and field measurements performed to develop the implementation of the full calibration chain of both binary and ADC channels are presented and discussed. The calibration procedure is reliable to work with the high amount of channels in the UMD, which will be operated continuously, in changing environmental conditions, for several years.
Ključne besede: ultra-high energy cosmic rays, extensive air showers (EAS), EAS muonic component, Pierre Auger Observatory, underground muon detector, detector calibration
Objavljeno v RUNG: 14.04.2021; Ogledov: 2637; Prenosov: 139
URL Povezava na celotno besedilo
Gradivo ima več datotek! Več...

167.
e/p separation study using the ISS-CREAM top and bottom counting detectors
S. C. Kang, Y. Amarea, D. Angelaszek, N. Anthony, G. H. Choi, M. Chung, M. Copley, L. Derome, L. Eraud, C. Falana, Jon Paul Lundquist, 2019, objavljeni znanstveni prispevek na konferenci

Opis: Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) is an experiment for studying the origin, acceleration, and propagation mechanisms of high-energy cosmic rays. The ISS-CREAM instrument was launched on the 14th of August 2017 to the ISS aboard the SpaceX-12 Dragon spacecraft. The Top and Bottom Counting Detectors (TCD/BCD) are parts of the ISS-CREAM instrument and designed for studying electron and gamma-ray physics. The TCD/BCD each consist of an array of 20 × 20 photodiodes on a plastic scintillator. The TCD/BCD can separate electrons from protons by using the difference between the shapes of electromagnetic and hadronic showers in the high energy region. The Boosted Decision Tree (BDT) method, which is a deep learning method, is used in this separation study. We will present results of the electron/proton separation study and rejection power in various energy ranges.
Ključne besede: instrumentations, high energy cosmic rays, particle detectors, composition
Objavljeno v RUNG: 08.02.2021; Ogledov: 2171; Prenosov: 0
Gradivo ima več datotek! Več...

168.
On-orbit performance of the ISS-CREAM calorimeter
K. C. Kim, Y. Amarea, D. Angelaszek, N. Anthony, G. H. Choi, M. Chung, M. Copley, L. Derome, L. Eraud, C. Falana, Jon Paul Lundquist, 2019, objavljeni znanstveni prispevek na konferenci

Opis: Cosmic Ray Energetics And Mass for the International Space Station (ISS-CREAM) experiment is designed to study the composition and energy spectra of cosmic-ray particles from 10^12 to 10^15 eV. ISS-CREAM was launched and deployed to the ISS in August 2017. The ISS-CREAM payload employs a Silicon Charge Detector for charge measurements, Top and Bottom Counting Detector for electron-hadron separation and a low-energy trigger, a Boronated Scintillator Detector for additional electron-hadron separation, and a Calorimeter (CAL) for en-ergy measurements and a high-energy trigger. The CAL is constructed of 20 layers of tungsten plates interleaved with scintillating fiber ribbons read out by hybrid-photodiodes (HPDs) and densified carbon targets. Each CAL layer is made of 3.5 mm (1 X_0) thick tungsten plates alter-nating with fifty 0.5 mm thick and 1 cm wide scintillating fiber ribbons. Consecutive layers of fiber ribbons are installed orthogonal to each other. Energy deposition in the CAL determines the particle energy and provides tracking information to determine which segment(s) of the charge detectors to use for the charge measurement. Tracking for showers is accomplished by extrapolating each shower axis back to the charge detectors. The performance of the ISS-CREAM CAL during flight is presented.
Ključne besede: instrumentations, high energy cosmic rays, particle detectors
Objavljeno v RUNG: 08.02.2021; Ogledov: 2307; Prenosov: 0
Gradivo ima več datotek! Več...

169.
ISS-CREAM flight operation
K. C. Kim, Y. Amarea, D. Angelaszek, N. Anthony, G. H. Choi, M. Chung, M. Copley, L. Derome, L. Eraud, C. Falana, Jon Paul Lundquist, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The Cosmic Ray Energetics And Mass experiment for the International Space Station (ISS-CREAM) is designed and built to measure the elemental energy spectra of cosmic-ray particles (1 ≤ Z ≤ 26) and electrons. It measures the energy of incident cosmic rays from 10^12 to 10^15 eV. ISS-CREAM was launched and deployed to the ISS in August 2017. The Science Operations Center (SOC) at the University of Maryland has been operating the payload on the International Space Station (ISS) in coordination with the Payload Operations Integration Center (POIC) at NASA’s Marshall Space Flight Center. The SOC has been responsible for sending commands to and receiving data from the Science Flight Computer (SFC) on board ISS-CREAM. The ISS-CREAM data taking program interfaces with the POIC using the Telescience Resources Kit through the Software Toolkit for Ethernet Lab-Like Architecture developed by the Boeing Company. The command uplink and data downlink have been through the Track-ing and Data Relay Satellite System. We present the ISS-CREAM flight operations including ISS communications, SFC performance, etc.
Ključne besede: instrumentations, high energy cosmic rays, particle detectors
Objavljeno v RUNG: 08.02.2021; Ogledov: 2250; Prenosov: 0
Gradivo ima več datotek! Več...

170.
On-orbit performance of the ISS-CREAM SCD
G. H. Choi, Y. Amarea, D. Angelaszek, N. Anthony, M. Chung, M. Copley, L. Derome, L. Eraud, C. Falana, Jon Paul Lundquist, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The Cosmic Ray Energetic And Mass for the International Space Station (ISS-CREAM) experiment is designed for precision measurements of energy spectra and elemental composition of cosmic rays. It was launched and installed on the ISS in August 2017. The Silicon Charge Detector (SCD), placed at the top of the ISS-CREAM payload, consists of 4 layers with a total of 10,752 silicon pixels which have 1.37 × 1.57 cm^2 size each. Each layer is arranged in such a fashion that its active detection area of 78 × 74 cm^2 is free of any dead area. The SCD 4-layer configuration was chosen to achieve the best precision in measuring the charge of cosmic rays from proton to iron nuclei with a charge resolution of 0.1 − 0.3e. We will present its on-orbit performance and operation status on the ISS since the launch.
Ključne besede: instrumentations, high energy cosmic rays, particle detectors
Objavljeno v RUNG: 08.02.2021; Ogledov: 2239; Prenosov: 0
Gradivo ima več datotek! Več...

Iskanje izvedeno v 0.06 sek.
Na vrh