3,416 research outputs found
Gamma-ray and neutrino signatures of Galactic cosmic-ray accelerators
No full textSupernova remnants are believed to be the major contributors to the observed Galactic cosmic-ray flux, though indisputable observational pieces of evidence of such statement are still missing. A crucial aspect of the supernova remnant para- digm for the origin of Galactic cosmic rays is that particle acceleration, as due to diffusive shock acceleration, requires effective confinement of particles in the shock region to let them achieve energies up to the so-called knee, around 1015 1016 eV. However, the current theoretical description of cosmic-ray acceleration and propagation within and around supernova remnants suffers from certain limitations, which also affect the predictions on the shape of the energy spectra of secondary gamma rays and neutrinos. In particular, in this thesis, two relevant aspects of this theory are investigated: the particle acceleration at shocks propagating in clumpy non-homogeneous environments and the particle escaping process from the acceleration site. The standard diffusive shock acceleration model usually assumes that shocks expand into ideally uniform environments, while a more realistic picture should consider an inhomogeneous gas distribution where supernova remnants develop. In this work, I conducted a detailed study on the particle acceleration and propagation through non-homogenous structures and its effect on the resulting secondary radiation. Regarding the particle escape from the acceleration site, I developed a phenomenological model to investigate this process and its impact on the gamma-ray emission from middle-aged supernova remnants, where particle escape is expected to be effective. I will show that spectroscopic and morphological studies of the gamma rays coming from both inside and immediately outside of those remnants can provide insight into the escaping process in general, and in particular, will shed light on their ability to act as cosmic-ray PeVatrons. So far, the only hint of the presence of a PeVatron has been found in the Galactic Center region, whose nature is, however, unclear. Under the assumption that the observed gamma-ray flux originates from hadronic interactions, I calculated the expected flux of multi-TeV neutrinos in order to investigate its detectability with future km3-scale neutrino telescopes. Finally, a comparative analysis of the performances of the two major upcoming detectors, namely CTA and KM3NeT, is presented in the context of future studies on the origin of Galactic cosmic rays through respectively gamma-ray and neutrino observations.
The thesis is organized as follows:
• In Chap. 1, the supernova remnant paradigm for the origin of cosmic rays is introduced and a discussion concerning possible Galactic PeV accelerators is presented. As gamma rays and neutrinos constitute observational signatures of particle acceleration and propagation, a review of their properties and detection techniques is provided.
• In Chap. 2, the propagation of accelerated particles within supernova remnants is investigated in the presence of strong shocks evolving through non-homogeneous media. A numerical approach to the particle transport under these conditions is here provided for the first time, conditions that represent realistic situations for the environments where sources as supernova remnants usually expand. Since dense molecular clumps constitute ideal targets for accelerated protons, enhanced gamma-ray and neutrino emissions are expected. The model is shown to provide an adequate description of the broadband gamma-ray emission of the Galactic supernova remnant RX J1713.7-3946 both in terms of total flux and spectral shape.
• In Chap. 3, a phenomenological description of particle escape from middle-aged supernova remnants is presented, and it represents the first attempt of studying this process within the context of extended sources. A proper description of this phenomenon is extremely relevant for the correct interpretation of the radiation spectrum observed in these sources, which reflects not only the acceleration mechanism and the interaction processes, but also the particle escape from the acceleration site. The model is applied to three interesting middle-aged Galactic supernova remnants, namely IC 443, W 51C, and W 28N. A major implication of the presence of particle escape is represented by the possible production of high-energy radiation also outside of the remnant shock, characterized by a very peculiar bump-like energy spectrum. This feature is interesting from the point of view of both gamma-ray and neutrino emissions, being experimentally con- nected to potentially background-free regions. Moreover, the escaping process is particularly relevant for a correct understanding of the cosmic-ray spectrum observed at Earth and to disentangle the propagation effects through the Galaxy.
• In Chap. 4, a candidate source of PeV cosmic rays located at the center of the Galaxy is discussed. The Galactic Center, as recently observed in multi-TeV gamma rays, shows a central emission with spectral cut-off energy at an energy of about 10 TeV. Nonetheless, a diffuse emission surrounding the central source shows no visible cut-off up to the energies currently probed by H.E.S.S.: the possibility of an intense infrared radiation field absorbing gamma rays from the central source is investigated for the first time. The detection of very high-energy neutrinos in angular correlation with the electromagnetic radiation would confirm the hadronic hypothesis for the origin of gamma rays. Hence, expectations from current and next-generation neutrino instruments are provided, indicating the relevance of a Northern Hemisphere detector for the
observation of this region with a clean event sample.
• In Chap. 5, the performances of the next-generation gamma-ray and neutrino
detectors are investigated, and differential sensitivities of CTA and KM3NeT for extended sources are derived. This study represents one of the first attempts towards the understanding of instrumental performances for extended sources related to spectroscopic detection of gamma rays through the imaging technique and capabilities of neutrino telescopes. Sensitivity analyses are, hence, applied to some interesting PeV cosmic-ray candidate sources, as the Galactic Center Ridge and the aforementioned supernova remnant RX J1713.7-3946.
• The main results of the work are summarized and discussed in Chap. 6.
The thesis contains three appendices, specifically separated from the text in order to facilitate its reading. In Appendix A, an overview of the equations regulating the magnetohydrodynamical properties of astrophysical plasma is presented, together with an insight into the numerical code adopted for the solution of this system of equations. In Appendix B, a detailed description of the numerical methods adopted for the solution of the particle transport equation in the presence of molecular clumps is provided. It is a technical appendix, intended to support the interested reader in reproducing the physical results discussed in Chap. 2. Its content repre- sents an original work developed by the author. Finally, Appendix C provides the mathematical framework developed in order to derive the analytical solution of the diffusive transport equation, satisfied by the escaping particle density function and presented in Chap. 3
A time-dependent search for high-energy neutrinos from bright GRBs with ANTARES
No full textAstrophysical point-like neutrino sources, like Gamma-Ray Bursts (GRBs), are one of the main targets for neutrino telescopes, since they are among the best candidates for Ultra-High-Energy Cosmic Ray (UHECR) acceleration. From the interaction between the accelerated protons and the intense radiation fields of the source jet, charged mesons are produced, which then decay into neutrinos. The methods and the results of a search for high-energy neutrinos in spatial and temporal correlation with the detected gamma-ray emission are presented for four bright GRBs observed between 2008 and 2013: a time-dependent analysis, optimised for each flare of the selected bursts, is performed to predict detailed neutrino spectra. The internal shock scenario of the fireball model is investigated, relying on the neutrino spectra computed through the numerical code NeuCosmA. The analysis is optimized on a per burst basis, through the maximization of the signal discovery probability. Since no events in ANTARES data passed the optimised cuts, 90% C.L. upper limits are derived on the expected neutrino fluences
Search for PeVatrons in VHE gamma rays and neutrinos
No full textSince its discovery more than one hundred years ago, the origin of the cosmic-ray (CR) flux measured on Earth is still unknown: in order to explain the region below the knee, supernova remnants (SNRs) are usually addressed as PeV cosmic accelerators. In particular, young SNRs are potential candidates since they might act as PeVatrons at least during the initial stage of their evolution. However, no clear indication of PeV energies has been observed so far in such a kind of sources, including the brightest TeV SNR, RX J1713-3946.7. Recently, the Galactic Center region has been detected as a very-high-energy (VHE) gamma-ray emitter. Two emission regions have been resolved by H.E.S.S.: a point source, spatially associated to the known radio source SgrA, and a diffuse flux, characterised by a simple power law gamma-ray spectrum with no visible cut-off up to gamma-ray energies of about 35 TeV. Such a detection triggers the search for PeVatron at the center of our Galaxy. A clear evidence of the hadronic nature of the emission would be the detection of a neutrino counterpart. I will here discuss the potentials of the next generation neutrino telescopes
Search for muon neutrinos from GRBs with the ANTARES neutrino telescope
No full textANTARES is the largest operational neutrino telescope in the Northern hemisphere, located in the deep water of the Mediterranean Sea, offshore Toulon. One of its main scientific goals concerns the identification of hadronic astrophysical accelerators through the detection of high-energy neutrinos. Among these sources, Gamma-Ray Bursts (GRBs) constitutes promising candidates because they are the most bright sources in the Universe. Their transient nature allows to drastically reduce the expected background when both a temporal and spatial correlation with the observed gamma-ray prompt emission is required. Cosmic neutrinos could be produced in the interaction between accelerated protons and intense radiation fields in the jet. Two different approaches have been adopted in the search: a stacked analysis with a sample of GRBs observable using the full ANTARES data set (from 2008 to 2016) and an individual search from some of the brightest GRBs (with gamma-ray fluence greater than 10-4 erg/cm2) occurred in the same time period. The methods and the results of these searches for muon neutrinos are here presented. The stacking analysis allows to constrain the contribution to the diffuse flux of neutrinos from this population of sources. In the bright GRB analysis, instead, the internal shock and the photospheric scenarios have been investigated and limits in the parameter space of the fireball model are derived individually. Since no events have been detected in spatial and temporal coincidence with GRBs in any of the searches, upper limits on neutrino fluence are derived both for individual bright sources and for the GRB population sample
Eloge
No full textOverview of the typology of the encomiastic epigram, from the archaic to the Byzantine period. Silvia Barbantani is author of the section on Greek epigram Rosario Moreno Soldevila is author of the section on the latin epigram
Sustainable food packaging from agro waste: from Nature for Nature
No full textWorld plastic production reached 368 million tons in 2019 and about 40% of them is used for the packaging sector. Recently, the problems related to the depletion of oil, from which the 98% of plastics derives, and to the plastic pollution, mainly due to not biodegradable materials, have driven research, industrial and end-user interests towards sustainable plastic products, derived from biomass and responding to the principles of recovery, reuse and recycling. In particular, the creation of a new packaging for the food sector, especially if intended for the packaging of organic food products, cannot ignore the logic of a sustainable development, as also requested by consumers who are increasingly attentive to concepts such as waste reduction, circularity of materials, food safety.
In this perspective, the research activity of the AgriCo.Pack project, funded by the Emilia Romagna Region, concerns the development of a packaging material for fresh fruit and vegetables, that is biobased and biodegradable / compostable and characterized by good performances. In particular, the new packaging is obtained by using a bio-based biodegradable polymer as the matrix and a high amount of fillers derived by agricultural production waste. The fillers are chosen according to their seasonality and availability and properly pre-treated, in order to improve their affinity with the polymeric matrix. The objective of the work is to produce polymeric bio-composites that can replace, in terms of performances and costs, materials derived from non-renewable and non-biodegradable sources. The project covers the full value chain, starting from agricultural companies, for the supply of vegetable waste, to research centers and companies interested in the development of the new packaging, designed also according to LCA analysis, to final end-users that will use a traceability system of the product
Gamma-ray emission from molecular clouds illuminated by local young massive stellar clusters and detection prospects with current and next generation instruments
No full textCosmic ray acceleration up to PeV energies has been suggested to take place in massive and young stellar clusters. The formation of a strong termination shock sustained by the collective action of stellar winds in a compact cluster offers a promising location where efficient particle acceleration might take place. The subsequent hadronic interactions of these particles result into gamma- ray production: in particular, if dense clouds are located within and around clusters, enhanced emission is expected. Within a scenario of particle acceleration at the cluster wind termination shock, we compute the emerging gamma-ray signal from molecular clouds illuminated by stellar clusters within the Milky Way. For this purpose, we adopt the Miville-Deschenes cloud catalog based on the Dame CO survey and astrometric observations of stellar clusters by GAIA. We further evaluate detection prospects of the gamma-ray flux with the Cherenkov Telescope Array (CTA) and the Large High Altitude Air Shower Observatory (LHAASO)
Supplementary_Table_S1_(1) - Fibrinogen Levels and the Risk of Cerebrovascular Events in Older Adults With Both Depressive Symptoms and Cognitive Impairment: A Prospective Study
No full textSupplementary_Table_S1_(1) for Fibrinogen Levels and the Risk of Cerebrovascular Events in Older Adults With Both Depressive Symptoms and Cognitive Impairment: A Prospective Study by Alessandra Bordignon, Caterina Trevisan, Maria Devita, Marianna Bizzotto, Silvia Celli, Agostino Girardi, Giuseppe Sergi, Maria Chiara Corti, Enzo Manzato and Alessandra Coin in Journal of Geriatric Psychiatry and Neurology</p
Oficina com jogos teatrais: instrumento auxiliar na ressignificação das relações interpessoais do profissional da saúde
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Educação. Programa de Pós-Graduação em EducaçãoA dissertação discute o potencial da oficina com jogos e exercícios teatrais como dinâmica no processo de ampliação da capacidade de comunicação ao profissional da saúde, a percepção e superação dos limites corporais, e, a busca de um maior entendimento de como pode ocorrer esse processo de diminuição da capacidade de comunicação e suas manifestações cotidianas. A autora utiliza como Metodologia a Pesquisa Qualitativa através do Estudo de Caso. Focaliza e analisa de modo particular duas experiências com oficinas de teatro Podem-se delinear a discussão da pesquisa em três etapas: Realização de duas oficinas dirigidas a profissionais da saúde; Descrição minuciosa de cada uma delas, para identificar através das falas dos sujeitos de pesquisa, uma prática formativa com potencial para colaborar e/ ou aumentar a capacidade de comunicação interpessoal ; Análise dos pontos mais significativos. Conclui que através desse Processo é possível sinalizar uma nova dinâmica de trabalho ao profissional da saúde, nas relações interpessoais com a equipe, com o paciente e respectiva família e comunidade. Sugere como proposta para repensar as questões de saúde e doença o referencial abordado pela Antropologia Médica
On the hadronic origin of the TeV radiation from GRB 190114C
No full textThe recently discovered TeV emission from Gamma-Ray Bursts (GRBs) has renewed the long-standing discussion about the hadronic versus leptonic origin of the observed GRB radiation. In this work, we investigate the possibility that the very high energy gamma rays observed by MAGIC from GRB 190114C (with energy from similar to 0.1 to similar to 0.8 TeV) are originated in a hadronic model. We developed a Monte Carlo (MC) simulation of the source internal state dynamics and of the photo-hadronic interactions at internal shock. We in-cluded in the simulation also the pair production process that the secondary gamma rays undergo in the GRB jet. We find upper limits on the internal shock model parameters by comparing our simulations to the sub-TeV observations of GRB 190114C. Neutrino flux predictions by the model are found to be consistent with experimental upper limits set by ANTARES and IceCube
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