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


1 - 10 / 29
Na začetekNa prejšnjo stran123Na naslednjo stranNa konec
1.
The Cherenkov Telescope Array sensitivity to the transient sky
Valentina Fioretti, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The Cherenkov Telescope Array (CTA) will be able to perform unprecedented observations of the transient very high-energy sky. An on-line science alert generation (SAG) pipeline, with a required 30 second latency, will allow the discovery or follow-up of gamma ray bursts (GRBs) and flaring emission from active galactic nuclei, galactic compact objects and electromagnetic counterparts of gravitational waves or neutrino messengers. The CTA sensitivity for very short exposures does not only depend on the technological performance of the array (e.g. effective area, background discrimination efficiency). The algorithms to evaluate the significance of the detection also define the sensitivity, together with their computational efficiency in order to satisfy the SAG latency requirements. We explore the aperture photometry and likelihood analysis techniques, and the associated parameters (e.g. on-source to off-source exposure ratio, minimum number of required signal events), defining the CTA ability to detect a significant signal at short exposures. The resulting CTA differential flux sensitivity as a function of the observing time, obtained using the latest Monte Carlo simulations, is compared to the sensitivities of Fermi–LAT and current-generation IACTs obtained in the overlapping energy ranges.
Ključne besede: very-high-energy gamma rays, Cherenkov Telescope Array (CTA) Observatory, transient astrophysical sources, gamma-ray bursts, active galactic nuclei
Objavljeno v RUNG: 15.11.2024; Ogledov: 277; Prenosov: 6
.pdf Celotno besedilo (784,43 KB)
Gradivo ima več datotek! Več...

2.
In situ identification of aerosol types in Athens, Greece, based on long-term optical and on online chemical characterization
Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, Eleni Liakakou, Umesh Chandra Dumka, Konstantinos Dimitriou, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2021, izvirni znanstveni članek

Opis: Absorption Ångström Exponent (AAE) and Scattering Ångström Exponent (SAE) values, derived from aethalometer and nephelometer measurements during a period of 3 years at an urban background site in Athens, are combined for the first aerosol type classification using in situ measurements in the eastern Mediterranean. In addition, single scattering albedo (SSA) and its wavelength dependence (dSSA), as well as the chemical composition of fine aerosols and precursor gases from collocated measurements, are utilized to provide further insights on the optical-chemical characterization and related sources of seven identified aerosol types. Urban aerosols are mostly characterized as Black Carbon (BC)-dominated (76.3%), representing a background atmosphere where fossil-fuel combustion is dominant throughout the year, while 14.3% of the cases correspond to the mixed Brown Carbon (BrC)-BC type, with a higher frequency in winter. The BrC type is associated with the highest scattering and absorption coefficients during winter nights, representing the impact from residential wood-burning emissions. Dust mixed with urban pollution (1.2%) and large particles mixed with BC (5.3%) have a higher frequency in spring. Furthermore, aging processes and BC coating with organic and inorganic species with weak spectral absorption (AAE<1) account for 2.2%, with a differentiation between small and large particles. dSSA is recognized as a useful parameter for aerosol characterization, since fine aerosols are associated with negative dSSA values. The identified aerosol types are examined on a seasonal, monthly, hourly basis and by potential source areas, as well as in comparison with fine-aerosol chemical composition and apportioned organic aerosol source contributions, in an attempt to explore the linkage between optical, physical and chemical aerosol properties. Chemical analysis indicates high organic fraction (60–68%) for the BrC and BrC/BC, 20–30% larger compared to other types. The results are essential for parametrization in chemical transport models and for reducing the uncertainty in the assessment of aerosol radiative effects.
Ključne besede: aerosol types, classification, AAE, SAE, dSSA, chemical composition, sources, Athens
Objavljeno v RUNG: 10.05.2024; Ogledov: 927; Prenosov: 4
URL Povezava na datoteko
Gradivo ima več datotek! Več...

3.
Particulate air pollution in the heart of the European Union : lessons learned from SAFICA 2017-2018 and SAAERO 2022-2023 projects in Central and Southeast Europe
Katja Džepina, Kristina Glojek, Martin Rigler, Asta Gregorič, Matic Ivančič, Irena Ježek, Griša Močnik, 2024, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Particularly during the cold weather season, countries of the Southeast Europe are experiencing some of the poorest air quality in the world due to the extensive use of solid fuels and old vehicle fleets. The city of Sarajevo is the capital of Bosnia and Herzegovina (BiH) situated within a basin surrounded by mountains. In the winter months (domestic heating season), topography and meteorology cause the pollutants to be trapped within the city basin. Countries of the Southeast Europe lack state-of-the-art atmospheric sciences research and access to sophisticated instrumentation and methodology, despite high levels of ambient pollution and position within the European Union (EU) borders, making it imperative to understand the emission sources, processing and the adverse health effects of atmospheric aerosol pollution.                This presentation will highlight the field measurements in Central and Southeast Europe during the Sarajevo Canton Winter Field Campaign 2017-2018 (SAFICA) and Sarajevo Aerosol Experiment 2022-2023 (SAAERO) projects, centered at the Sarajevo Bjelave supersite. Both projects were envisioned to produce crucial, not previously available information about aerosol emission sources and atmospheric transformations through a combination of online field and offline laboratory measurements. Online measurements during a) SAFICA and b) SAAERO included, a) black carbon, particle number and size distribution, and b) carbonaceous species, elemental composition and bulk chemical composition. SAAERO online measurements also included stationary and mobile measurements of gas- and particle-phase species on board the mobile laboratory in Sarajevo and Zenica, BiH, as well as in Ljubljana, Slovenia and Zagreb, Croatia. Finally, extended SAAERO project included measurements of black carbon at three additional urban centers: Ljubljana, Zagreb, and Belgrade, Serbia, enabling the first comparison of urban air quality in Central and Southeast Europe between two EU and two non-EU capitals. During both projects, laboratory aerosol analyses determined aerosol bulk chemical composition, selected elements (Huremović et al., 2020; Žero et al., 2022) and molecular species (Pehnec et al., 2020). Aerosol chemical composition determined by aerosol mass spectrometry was further analyzed by Positive Matrix Factorization to separate organic aerosol into subtypes characteristic of specific sources and atmospheric processes. Aerosol oxidative potential was also determined to evaluate aerosol ability to generate reactive oxygen species. Sarajevo and Belgrade have high ambient loadings of aerosol and black carbon, indicative of strong and diverse combustion sources and a major public health hazard. Finally, aerosol surface concentrations will be discussed in the context of European air quality. We thank Jasminka Džepina, Magee Scientific/Aerosol, TSI and Aerodyne for support. We acknowledge the contribution of the COST Action CA16109 COLOSSAL and SEE Change Net. KDž and ASHP acknowledge the grant by the Swiss NSF (Scientific Exchanges IZSEZ0_189495), KDž, GM and ASHP European Commission SAAERO grant (EU H2020 MSCA-IF 2020 #101028909), GM Slovenian ARIS grant (P1-0385), SF Croatian HRZZ grant (BiREADI IP-2018-01-3105), and AG, MR, MI, BA and IBJ Slovenian ARIS grant (L1-4386). Pehnec, G., et al., Sci. Tot. Environ., 734, 139414, 2020. Huremović, J., et al., Air Qual. Atmos. Health, 13, 965–976, 2020. Žero, S., Žužul, S., et al., Environ. Sci. Technol., 56, 7052−7062, 2022.
Ključne besede: air pollution, sources of pollution, PMF
Objavljeno v RUNG: 18.03.2024; Ogledov: 2306; Prenosov: 7
.pdf Celotno besedilo (314,28 KB)
Gradivo ima več datotek! Več...

4.
Anisotropy studies of ultra-high-energy cosmic rays measured at the Pierre Auger Observatory
Josina Schulte, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Measurements of anisotropic arrival directions of ultra-high-energy cosmic rays provide important information for identifying their sources. On large scales, cosmic rays with energies above 8 EeV reveal a dipolar flux modulation in right ascension with a significance of 6.9 deg., with the dipole direction pointing 113◦ away from the Galactic center. This observation is explained by extragalactic origins. Also, model-independent searches for small- and intermediate-scale overdensities have been performed in order to unveil astrophysically interesting regions. On these scales, no statistically significant features could be detected. However, intermediate-scale analyses comparing the measured arrival directions with potential source catalogs show indications for a coincidence of the measured arrival directions with catalogs of starburst galaxies and the Centaurus A region. In this contribution, an overview of the studies regarding anisotropies of the arrival directions of ultra-high-energy cosmic rays measured at the Pierre Auger Observatory on different angular scales is presented and the current results are discussed.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, UHECR anisotropy studies, UHECR sources
Objavljeno v RUNG: 24.01.2024; Ogledov: 2353; Prenosov: 8
.pdf Celotno besedilo (5,01 MB)
Gradivo ima več datotek! Več...

5.
Investigation of multi-messenger properties of FR0 radio galaxy emitted ultra-high energy cosmic rays
Jon Paul Lundquist, Lukas Merten, Serguei Vorobiov, Margot Boughelilba, Albert Reimer, Paolo Da Vela, F. Tavecchio, G. Bonnoli, C. Righi, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Low luminosity Fanaroff-Riley type 0 (FR0) radio galaxies are amongst potential contributors to the observed flux of ultra-high energy cosmic rays (UHECRs). Due to FR0s’ much higher abundance in the local universe than more powerful radio galaxies (e.g., about five times more ubiquitous at redshifts z≤0.05 than FR1s), they could provide a substantial fraction of the total UHECR energy density. In the presented work, we determine the mass composition and energy spectrum of UHECRs emitted by FR0 sources by fitting simulation results from the CRPropa3 framework to the recently published Pierre Auger Observatory data. The resulting emission spectral characteristics (spectral indices, rigidity cutoffs) and elemental group fractions are compared to the Auger results. The FR0 simulations include the approximately isotropic distribution of FR0s extrapolated from the measured FR0 galaxy properties and various extragalactic magnetic field configurations, including random and large-scale structured fields. We predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. The presented results allow for probing the properties of the FR0 radio galaxies as cosmic-ray sources using observational high-energy multi-messenger data.
Ključne besede: ultra-high energy cosmic rays, UHECRs, Pierre Auger Observatory, UHECR propagation, UHECR interactions, UHECR energy spectrum, UHECR mass composition, UHECR sources, Fanaroff-Riley (FR) radio galaxies, FR0 galaxies
Objavljeno v RUNG: 24.01.2024; Ogledov: 1521; Prenosov: 40
.pdf Celotno besedilo (573,28 KB)
Gradivo ima več datotek! Več...

6.
Cherenkov Telescope Array Science : a multi-wavelength and multi-messenger perspective
Ulisses Barres de Almeida, Christopher Eckner, Gašper Kukec Mezek, Samo Stanič, Serguei Vorobiov, Lili Yang, Gabrijela Zaharijas, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: The Cherenkov Telescope Array (CTA) will be the major global observatory for VHE gamma-ray astronomy over the next decade and beyond. It will be an explorer of the extreme universe, with a broad scientific potential: from understanding the role of relativistic cosmic particles, to the search for dark matter. Covering photon energies from 20 GeV to 300 TeV, and with an angular resolution unique in the field, of about 1 arc min, CTA will improve on all aspects of the performance with respect to current instruments, surveying the high energy sky hundreds of times faster than previous TeV telescopes, and with a much deeper view. The very large collection area of CTA makes it an important probe of transient phenomena. The first CTA telescope has just been inaugurated in the Canary Islands, Spain, and as more telescopes are added in the coming years, scientific operation will start. It is evident that CTA will have important synergies with many of the new generation astronomical and astroparticle observatories. In this talk we will review the CTA science case from the point of view of its synergies with other instruments and facilities, highlighting the CTA needs in terms of external data, as well as the opportunities and strategies for cooperation to achieve the basic CTA science goals.
Ključne besede: very-high-energy gamma-ray astronomy, Cherenkov Telescope Array, CTA performances, transient VHE sources, CTA science
Objavljeno v RUNG: 04.12.2023; Ogledov: 2654; Prenosov: 6
.pdf Celotno besedilo (1,16 MB)
Gradivo ima več datotek! Več...

7.
8.
Performance study update of observations in divergent mode for the Cherenkov Telescope Array
A. Donini, Saptashwa Bhattacharyya, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Due to the limited field of view (FoV) of Cherenkov telescopes, the time needed to achieve target sensitivity for surveys of the extragalactic and Galactic sky is large. To optimize the time spent to perform such surveys, a so-called “divergent mode” of the Cherenkov Telescope Array Observatory (CTAO) was proposed as an alternative observation strategy to the traditional parallel pointing. In the divergent mode, each telescope points to a position in the sky that is slightly offset, in the outward direction, from the original center of the field of view. This bring the advantage of increasing the total instantaneous arrays’ FoV. From an enlarged field of view also benefits the search for very-high-energy transient sources, making it possible to cover large sky regions in follow-up observations, or to quickly cover the probability sky map in case of Gamma Ray Bursts (GRB), Gravitational Waves (GW), and other transient events. In this contribution, we present the proposed implementation of the divergent pointing mode and its first preliminary performance estimation for the southern CTAO array.
Ključne besede: Cherenkov Telescope Array, CTAO, divergent mode, very-high-energy transient sources
Objavljeno v RUNG: 26.09.2023; Ogledov: 1556; Prenosov: 7
.pdf Celotno besedilo (554,96 KB)
Gradivo ima več datotek! Več...

9.
Sensitivity of the Cherenkov Telescope Array to the gamma-ray emission from neutrino sources detected by IceCube
Olga Sergijenko, Saptashwa Bhattacharyya, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, Miha Živec, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Gamma-ray observations of the astrophysical neutrino sources are fundamentally important for understanding the underlying neutrino production mechanism. We investigate the Cherenkov Telescope Array (CTA) ability to detect the very-high-energy (VHE) gamma-ray counterparts to the neutrino-emitting Active Galaxies. The CTA performance under different configurations and array layouts is computed based on the neutrino and gamma-ray simulations of steady and transient types of sources, assuming that the neutrino events are detected with the IceCube neutrino telescope. The CTA detection probability is calculated for both CTA sites taking into account the visibility constraints. We find that, under optimal observing conditions, CTA could observe the VHE gamma-ray emission from at least 3 neutrino events per year.
Ključne besede: Cherenkov Telescope Array, IceCube neutrino telescope, neutrinos, neutrino sources
Objavljeno v RUNG: 26.09.2023; Ogledov: 2192; Prenosov: 8
.pdf Celotno besedilo (1,08 MB)
Gradivo ima več datotek! Več...

10.
Exploring the population of Galactic very-high-energy γ-ray sources
Constantin Steppa, Saptashwa Bhattacharyya, Barbara MARČUN, Judit Pérez Romero, Samo Stanič, Veronika Vodeb, Serguei Vorobiov, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, objavljeni znanstveni prispevek na konferenci

Opis: At very high energies (VHE), the emission of γ rays is dominated by discrete sources. Due to the limited resolution and sensitivity of current-generation instruments, only a small fraction of the total Galactic population of VHE γ-ray sources has been detected significantly. The larger part of the population can be expected to contribute as a di˙use signal alongside emission originating from propagating cosmic rays. Without quantifying the source population, it is not possible to disentangle these two components. Based on the H.E.S.S. Galactic plane survey, a numerical approach has been taken to develop a model of the population of Galactic VHE γ-ray sources, which is shown to account accurately for the observational bias. We present estimates of the absolute number of sources in the Galactic Plane and their contribution to the total VHE γ-ray emission for five di˙erent spatial source distributions. Prospects for CTA and its ability to constrain the model are discussed. Finally, first results of an extension of our modelling approach using machine learning to extract more information from the available data set are presented.
Ključne besede: Cherenkov Telescope Array, very-high energy gamma-rays, gamma-ray sources
Objavljeno v RUNG: 18.09.2023; Ogledov: 1438; Prenosov: 6
.pdf Celotno besedilo (744,16 KB)
Gradivo ima več datotek! Več...

Iskanje izvedeno v 0.04 sek.
Na vrh