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High-energy emission from a magnetar giant flare in the Sculptor galaxy
Gabrijela Zaharijas, 2021, original scientific article

Found in: ključnih besedah
Summary of found: ...magnetars, gamma-ray astronomy, transients...
Keywords: magnetars, gamma-ray astronomy, transients
Published: 14.01.2021; Views: 592; Downloads: 0
.pdf Fulltext (2,28 MB)

Observations of the origin of downward terrestrial gamma-ray flashes
M. A. Stanley, R. U. Abbasi, R. LeVon, W. Rison, D. Rodeheffer, T. Abu-Zayyad, Jon Paul Lundquist, P. R. Krehbiel, J. Remington, J. W. Belz, 2020, original scientific article

Abstract: In this paper we report the first close, high‐resolution observations of downward‐directed terrestrial gamma‐ray flashes (TGFs) detected by the large‐area Telescope Array cosmic ray observatory, obtained in conjunction with broadband VHF interferometer and fast electric field change measurements of the parent discharge. The results show that the TGFs occur during strong initial breakdown pulses (IBPs) in the first few milliseconds of negative cloud‐to‐ground and low‐altitude intracloud flashes and that the IBPs are produced by a newly identified streamer‐based discharge process called fast negative breakdown. The observations indicate the relativistic runaway electron avalanches (RREAs) responsible for producing the TGFs are initiated by embedded spark‐like transient conducting events (TCEs) within the fast streamer system and potentially also by individual fast streamers themselves. The TCEs are inferred to be the cause of impulsive sub‐pulses that are characteristic features of classic IBP sferics. Additional development of the avalanches would be facilitated by the enhanced electric field ahead of the advancing front of the fast negative breakdown. In addition to showing the nature of IBPs and their enigmatic sub‐pulses, the observations also provide a possible explanation for the unsolved question of how the streamer to leader transition occurs during the initial negative breakdown, namely, as a result of strong currents flowing in the final stage of successive IBPs, extending backward through both the IBP itself and the negative streamer breakdown preceding the IBP.
Found in: ključnih besedah
Keywords: terrestrial gamma-ray flashes, lightning, fast breakdown, initial breakdown pulse, atmospheric electricity, transient conducting events
Published: 04.02.2021; Views: 662; Downloads: 3
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Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre
Christopher Eckner, A. Aguirre-Santaella, I. Agudo, C. Adams, R. Adam, A. Acharyya, Samo Stanič, Serguei Vorobiov, Gabrijela Zaharijas, Marko Zavrtanik, Danilo Zavrtanik, Miha Živec, 2021, original scientific article

Found in: ključnih besedah
Summary of found: ...dark matter, gamma ray, astrophysics...
Keywords: dark matter, gamma ray, astrophysics
Published: 26.02.2021; Views: 580; Downloads: 21
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Study of axion-like particles signatures in the very-high-energy gamma-ray spectra of Active Galactic Nuclei
Ivana Batković, 2020, master's thesis

Found in: ključnih besedah
Keywords: axions, dark matter, gamma-ray astrophysics
Published: 26.02.2021; Views: 757; Downloads: 0
.pdf Fulltext (12,57 MB)

Studying dark matter annihilation in Perseus galaxy cluster using very-high-energy gamma rays
Nemanja Ivković, 2020, master's thesis

Found in: ključnih besedah
Keywords: dark matter, gamma-ray astrophysics
Published: 01.03.2021; Views: 571; Downloads: 0
.pdf Fulltext (7,17 MB)

On velocity-dependent dark matter annihilations in dwarf satellites
Mauro Valli, Piero Ullio, Mihael Petač, 2018, original scientific article

Abstract: 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.
Found in: ključnih besedah
Summary of found: ...been recent reassessments of the expected DM gamma-ray signals in case of long-range interactions, commonly...
Keywords: dark matter, indirect detection, dwarf satellites, sommerfeld enhancement, gamma-rays
Published: 01.10.2021; Views: 115; Downloads: 2 
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Localisation and classification of gamma ray sources using neural networks
Guõlaugur Jóhannesson, Roberto Ruiz de Austri, Gabrijela Zaharijas, Sascha Caron, Boris Panes, Saptashwa Bhattacharyya, Chris van den Oetelaar, 2021, published scientific conference contribution

Abstract: With limited statistics and spatial resolution of current detectors, accurately localising and separating gamma-ray point sources from the dominating interstellar emission in the GeV energy range is challenging. Motivated by the challenges of the traditional methods used for the gamma-ray source detection, here we demonstrate the application of deep learning based algorithms to automatically detect and classify point sources, which can be applied directly to the binned Fermi-LAT data and potentially be generalised to other wavelengths. For the point source detection task, we use popular deep neural network structure U-NET, together with image segmentation, for precise localisation of sources, various clustering algorithms were tested on the segmented images. The training samples are based on the source properties of AGNs and PSRs from the latest Fermi-LAT source catalog, in addition to the background interstellar emission. Finally, we have created a more complex but robust training data generation exploiting full detector potential, increasing spatial resolution at the highest energies.
Found in: ključnih besedah
Keywords: gamma-rays, deep learning, computer vision
Published: 01.10.2021; Views: 114; Downloads: 2
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