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Opis: The Cherenkov Telescope Array (CTA) is the next generation high-energy gamma-ray observatory. It will improve the sensitivity of current instruments up to an order of magnitude, while providing energy coverage for photons from 20 GeV to at least 300 TeV to reach high redshifts and extreme accelerators and will give access to the shortest time-scale phenomena. CTA is thus a uniquely powerful instrument for the exploration of the violent and variable universe. The ability to probe short timescales at the highest energies will allow CTA to explore the connection between accretion and ejection phenomena surrounding compact objects, investigate the processes occurring in relativistic outflows, and open up significant phase space for serendipitous discoveries. Aiming at playing a central role in the era of multi-messenger astrophysics, the CTA Transient program includes follow-up observations of a broad range of multi-wavelength and multi-messenger alerts, ranging from Galactic compact object binary systems to novel phenomena like Fast Radio Bursts. A promising case is that of gamma-ray bursts (GRBs), where CTA will for the first time enable high-statistics measurements above ∼ 10 GeV, probing new spectral components and shedding light on the physical processes at work in these systems. Dedicated programs searching for very-high-energy (VHE) gamma-ray counterparts to gravitational waves and high-energy neutrinos complete the CTA transients program. This contribution will introduce and outline the CTA Transients program. We will provide an overview of the various science topics and discuss the links to multi-messenger and multi-wavelength observations.
Ključne besede: very-high-energy (VHE) gamma rays, the Cherenkov Telescope Array (CTA) Observatory, transient astrophysical phenomena, relativistic outflows, gamma-ray bursts
Objavljeno v RUNG: 12.11.2024; Ogledov: 880; Prenosov: 5
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Opis: One of the major scientific objectives of the future Cherenkov Telescope Array (CTA) Observatory is the search for PeVatrons. PeVatrons are cosmic-ray factories able to accelerate nuclei at least up to the knee feature seen in the spectrum of cosmic rays measured near the Earth. CTA will perform a survey of the full Galactic plane at TeV energies and beyond with unprecedented sensitivity. The determination of efficient criteria to identify PeVatron candidates during the survey is essential in order to trigger further dedicated observations. Here, we present results from a study based on simulations to determine these criteria. The outcome of the study is a PeVatron figure of merit, defined as a metric that provides relations between spectral parameters and spectral cutoff energy lower limits. In addition, simulations of the PeVatron candidate HESS J1641−463 and its parental particle spectrum are presented and discussed. Eventually, our work is applied to simulated population of Galactic PeVatrons, with the aim to determine the sensitivity of CTA.
Ključne besede: Galactic cosmic rays, very-high-energy gamma rays, Galactic PeVatrons, Cherenkov Telescope Array (CTA) Observatory, Galactic plane survey, H.E.S.S. J1641−463 PeVatron candidate
Objavljeno v RUNG: 08.11.2024; Ogledov: 848; Prenosov: 6
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Opis: The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for γ-ray astronomy at energies above 30 GeV. Thanks to its unique capabilities, CTA observations will address a plethora of open questions in astrophysics, ranging from the origin of cosmic messengers to the exploration of the frontiers of physics. In this note, we present a comprehensive sensitivity study to assess the potential of CTA to measure the γ-ray absorption on the extragalactic background light (EBL), to constrain or detect intergalactic magnetic fields (IGMFs), and probe physics beyond the standard model such as axion-like particles (ALPs) and Lorentz invariance violation (LIV), which could modify the γ-ray spectra features expected from EBL absorption. Our results suggest that CTA will have unprecedented sensitivity to detect IGMF signatures and will probe so-far unexplored regions of the LIV and ALP parameter space. Furthermore, an indirect measurement of the EBL and of its evolution will be performed with unrivaled precision.
Ključne besede: very-high-energy gamma rays, the Cherenkov Telescope Array (CTA) Observatory, extragalactic background light (EBL), intergalactic magnetic fields (IGMFs), axion-like particles (ALPs), Lorentz invariance violation (LIV)
Objavljeno v RUNG: 07.11.2024; Ogledov: 833; Prenosov: 5
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Opis: Approximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way, detected with a combination of targeted observations and surveys. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from recent observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the three main classes of established Galactic VHE sources (pulsar wind nebulae, young and interacting supernova remnants, and compact binary systems), as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy (pointing pattern and scheduling) based on recent estimations of the instrument performance. We use the improved sky model and observation strategy to simulate GPS data corresponding to a total observation time of 1620 hours spread over ten years. Data are then analysed using the methods and software tools under development for real data. Under our model assumptions and for the realisation considered, we show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, to confirm the existence of a hypothetical population of gamma-ray pulsars with an additional TeV emission component, and to detect bright sources capable of accelerating particles to PeV energies (PeVatrons). Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. Thus, a survey of the entire Galactic plane carried out from both hemispheres with CTAO will ensure a transformational advance in our knowledge of Galactic VHE source populations and interstellar emission.
Ključne besede: very-high-energy gamma rays, Cherenkov Telescope Array Observatory, CTAO Galactic Plane Survey, galactic cosmic rays, pulsar wind nebulae, supernova remnants, galactic PeVatrons, binary systems, diffuse emission
Objavljeno v RUNG: 28.10.2024; Ogledov: 1064; Prenosov: 4
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Opis: The Pierre Auger Observatory is sensitive to ultra-high energy neutral particles, such as photons, neutrinos, and neutrons, and can take part in Multi-Messenger searches in collaboration with other observatories. Photons and neutrinos are searched by exploiting the design of the Pierre Auger Observatory and profiting from the different properties of the induced showers caused by different particles. Diffuse and point source fluxes of photons and neutrinos are searched for. Furthermore, photon and neutrino follow-ups of the gravitational wave events observed by the LIGO/Virgo Collaboration are conducted. The Pierre Auger Observatory is also used to search for neutrons from point-like sources. In contrast to photons and neutrinos, neutrons induce air showers that cannot be distinguished from those produced by protons. For this reason, the search for neutrons from a given source is performed by searching for an excess of air showers from the corresponding direction. All these searches have resulted in stringent upper limits on the corresponding fluxes of the considered particles, allowing, together with the results obtained by other experiments, to shed some light on the most energetic phenomena of our Universe. An overview of the Multi-Messenger activities carried out within the Pierre Auger Collaboration is presented.
Ključne besede: ultra-high-energy cosmic rays, UHE photons, UHE neutrinos, UHE neutrons, Pierre Auger Observatory, multi-messenger astrophysical studies
Objavljeno v RUNG: 04.10.2024; Ogledov: 1116; Prenosov: 6
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