VLBI and gamma-ray studies of radio galaxies in the TANAMI monitoring program

Relativistic jets in Active Galactic Nuclei (AGN) are among the most extreme sources of radiation in the universe. They are launched and accelerated by accreting supermassive black holes found in the center of a fraction of galaxies. These jets emit strongly across the whole electromagnetic spectrum, and are especially bright in the radio and gamma-ray bands, where they are among the most studied astrophysical sources. In the simplest models, the production of gamma-rays in radio-loud AGN involves the same relativistic particles that give rise to the radio emission. Therefore, we expect to observe a close connection between the two bands. This has been well-established in studies of large AGN samples. However, such samples are dominated by AGN with well-aligned jets, a sub-class called blazars, where the observed emission is strongly beamed and amplified due to relativistic Doppler effects. While this makes blazars easier to detect, it also poses the challenge of disentangling orientation-dependent effects from the intrinsic physical properties. To this date, there has been no systematic study on the relation between parsec-scale radio emission and gamma-ray properties of the misaligned parent population of blazars, i.e., radio galaxies. In this thesis, I present the first systematic VLBI and gamma-ray monitoring study of a representative sample of radio galaxies with strong compact radio emission, with the aim of exploring the intrinsic relationship between high-energy emission and pc-scale jet properties in AGN. I base the study on the decade(s)-long Very Long Baseline Interferometry (VLBI) monitoring provided by the TANAMI program, the largest multi-epoch observational campaign on radio-loud AGN in the Southern sky. First, I introduce the basic properties of AGN (Chapter 1), and discuss the current understanding of the relation between radio and gamma-ray emission in AGN (Chapter 2). I then introduce the instruments and the corresponding data reduction techniques relevant to this thesis work, i.e., gamma-ray telescopes (Chapter 3) and VLBI arrays (Chapter 4). Chapter 5 presents the results on the evolution of the parsec-scale jet in TANAMI radio galaxies, including milliarcsecond resolution images at 8.4 GHz for several observing epochs, and a jet kinematic analysis to estimate the intrinsic jet speed, viewing angle, and overall evolution, at the highest resolution available for this sample. The information from parsec-scale jet kinematics is combined with gamma-ray flux variability results from the Fermi -LAT space telescope (presented in Chapter 6), and the observed properties in these two bands and their interplay are discussed in Chapter 7. I summarize the main results in Chapter 8.I first discuss individual results on noteworthy TANAMI radio galaxies, such as the FR II radio galaxy Pictor A, the peculiar AGN PKS 0521−36, the TeV source PKS 0625−35, and the first gamma-ray detected young radio galaxy, PKS 1718−649 (Section 7.1). I then combine the TANAMI radio galaxy sample with publicly available results from the MOJAVE survey, the largest VLBI monitoring program of AGN in the northern sky, to study the largest sample to date of radio galaxies with parsec-scale kinematics and gamma-ray information (Section 7.2). Testing for possible correlations between the average radio and gamma-ray properties of radio galaxies, I show that the high-energy emission from the compact jets of radio galaxies is not strongly driven by orientation-dependent Doppler boosting effects, much unlike the situation in their blazar counterparts. However, a significant correlation between gamma-ray flux and radio flux still holds, suggesting a direct physical link between the intrinsic emission properties of AGN jets in the two wavebands

Revisiting the TeV detection prospects for radio galaxies

Radio galaxies host relativistic jets oriented away from our line of sight, making them challenging targets for Very High Energy (VHE, E$>$100 GeV) $\gamma$-ray detectors. Indeed, out of $\sim100$ extragalactic sources detected at $E>100$ GeV, only six are radio galaxies. The new Cherenkov Telescope Array (CTA) will provide order-of-magnitude improvements in sensitivity with respect to the present generation of ground-based $\gamma$-ray observatories, opening new frontiers for high-energy studies of radio galaxies. In a previous paper, we studied the CTA detection prospects of misaligned jets from the Third Fermi-LAT catalog (3FGL) sample. In this work, we take advantage of the expanded sample from the Fourth Fermi-LAT catalog (4FGL), including roughly double the number of sources. We simulate CTA observations of 41 $\gamma$-ray radio galaxies, extrapolating their GeV spectrum into the TeV range assuming different spectral shapes. We predict that the CTA will detect eleven new TeV radio galaxies with an observational campaign of 50 hours per source, under the realistic assumption of a spectral cutoff at 0.5 TeV. This would increase the sample of VHE radio galaxies by a factor of three, and result in the first detection of FR II radio galaxies at these energies. By simulating CTA observations with 5 hours exposure, we predict that two Fermi-LAT radio galaxies should already be within reach of current TeV observatories. Finally we have investigated the prospects for a CTA detection of extended VHE emission from the lobe-dominated FR I Fornax A, and predict that this will be possible for integration times $\gtrsim\!50$ hours. We conclude that the CTA will significantly impact our understanding of misaligned jets at TeV energies, allowing us to perform population studies and compare the two main radio galaxy subclasses for the first time in this energy band.Comment: Accepted for publication in Astroparticle Physics. 19 pages (main text 11 pages), 3 figures, 4 table

Oxidative stress by the mitochondrial monoamine oxidase B mediates calcium pyrophosphate crystal-induced arthritis

Objective: Calcium pyrophosphate (CPP) crystal deposition in the joints is associated with a heterogeneous set of debilitating syndromes characterized by inflammation and pain, for which no effective therapies are currently available. As we found that the mitochondrial enzyme monoamine oxidase B (MAO-B) plays a fundamental role in promoting inflammatory pathways, this study aims at assessing the efficacy of two clinical-grade inhibitors (iMAO-Bs) in preclinical models of this disease, to pave the way for a novel treatment. Methods: We tested our hypothesis in two murine models of CPP-induced arthritis, by measuring cytokine and chemokine levels, along with immune cell recruitment. iMAO-Bs (rasagiline and safinamide) were administered either before or after crystal injection. To elucidate the molecular mechanism, we challenged in vitro primed macrophages with CPP crystals and assessed the impact of iMAO-Bs in dampening proinflammatory cytokines and in preserving mitochondrial function. Results: Both in preventive and therapeutic in vivo protocols, iMAO-Bs blunted the release of proinflammatory cytokines (interleukin (IL)-6 and IL1-β) and chemokines (CXCL10, CXCL1, CCL2 and CCL5) (n>6 mice/group). Importantly, they also significantly reduced ankle swelling (50.3% vs 17.1% [P<0.001] and 23.1% [P=0.005] for rasagiline and safinamide, respectively). Mechanistically, iMAO-Bs dampened the burst of reactive oxygen species (ROS) and the mitochondrial dysfunction triggered by CPP crystals in isolated macrophages. Moreover, iMAO-Bs blunted cytokine secretion and NLRP3 inflammasome activation through inhibition of the NF-κB and STAT3 pathways. Conclusion: iMAO-Bs dampen inflammation in murine models of crystal-induced arthropathy, thereby uncovering MAO-B as a promising target to treat these diseases

DART: the distributed agent based retrieval toolkit

The technology of search engines is evolving from indexing and classification of web resources based on keywords to more sophisticated techniques which take into account the meaning and the context of textual information and usage. Replying to query, commercial search engines face the user requests with a large amount of results, mostly useless or only partially related to the request; the subsequent refinement, operated downloading and examining as much pages as possible and simply ignoring whatever stays behind the first few pages, is left up to the user. Furthermore, architectures based on centralized indexes, allow commercial search engines to control the advertisement of online information, in contrast to P2P architectures that focus the attention on user requirements involving the end user in search engine maintenance and operation. To address such wishes, new search engines should focus on three key aspects: semantics, geo-referencing, collaboration/distribution. Semantic analysis lets to increase the results relevance. The geo-referencing of catalogued resources allows contextualisation based on user position. Collaboration distributes storage, processing, and trust on a world-wide network of nodes running on users’ computers, getting rid of bottlenecks and central points of failures. In this paper, we describe the studies, the concepts and the solutions developed in the DART project to introduce these three key features in a novel search engine architecture

Looking for the first time into the heart of the blazar TXS 2013+370

The compact radio source TXS 2013+370 is a γ-ray blazar which is located at a redshift of z = 0.859 at a galactic latitude b = 1.2°. We observed the source with Very Long Baseline Interferometry (VLBI) at 15, 43 and 86 GHz and studied the morphology and the kinematic properties of the jet. The VLBI data were then combined with flux density variability measurements at 15 and 235 GHz and with the available γ-ray light curve in the period 2008-2017. A cross-correlation analysis was performed to investigate the existence of a correlation between the variability observed in the different bands. The preliminary results of our study showed that the most prominent flares and maxima stem from the central VLBI region and most likely are associated with the nuclear region, namely the core, indicating that the activity is caused by the passage of traveling shocks through the core region. In the course of our analysis, we present for the first time a 86 GHz Global Millimeter VLBI Array (GMVA) image of the innermost jet region

A collaborative, semantic and context-aware search engine

Search engines help people to find information in the largest public knowledge system of the world: the Web. Unfortunately its size makes very complex to discover the right information. The users are faced lots of useless results forcing them to select one by one the most suitable. The new generation of search engines evolve from keyword-based indexing and classification to more sophisticated techniques considering the meaning, the context and the usage of information. We argue about the three key aspects: collaboration, geo-referencing and semantics. Collaboration distributes storage, processing and trust on a world-wide network of nodes running on users’ computers, getting rid of bottlenecks and central points of failures. The geo-referencing of catalogued resources allows contextualisation based on user position. Semantic analysis lets to increase the results relevance. In this paper, we expose the studies, the concepts and the solutions of a research project to introduce these three key features in a novel search engine architecture.213-21

Looking for the first time into the heart of the blazar TXS 2013+370

The compact radio source TXS 2013+370 is a γ-ray blazar which is located at a redshift of z = 0.859 at a galactic latitude b = 1.2°. We observed the source with Very Long Baseline Interferometry (VLBI) at 15, 43 and 86 GHz and studied the morphology and the kinematic properties of the jet. The VLBI data were then combined with flux density variability measurements at 15 and 235 GHz and with the available γ-ray light curve in the period 2008-2017. A cross-correlation analysis was performed to investigate the existence of a correlation between the variability observed in the different bands. The preliminary results of our study showed that the most prominent flares and maxima stem from the central VLBI region and most likely are associated with the nuclear region, namely the core, indicating that the activity is caused by the passage of traveling shocks through the core region. In the course of our analysis, we present for the first time a 86 GHz Global Millimeter VLBI Array (GMVA) image of the innermost jet region

Human Leukocyte Antigen Complex and Other Immunogenetic and Clinical Factors Influence Susceptibility or Protection to SARS-CoV-2 Infection and Severity of the Disease Course. The Sardinian Experience

Aim: SARS-CoV-2 infection is a world-wide public health problem. Several aspects of its pathogenesis and the related clinical consequences still need elucidation. In Italy, Sardinia has had very low numbers of infections. Taking advantage of the low genetic polymorphism in the Sardinian population, we analyzed clinical, genetic and immunogenetic factors, with particular attention to HLA class I and II molecules, to evaluate their influence on susceptibility to SARS-CoV-2 infection and the clinical outcome. Method and Materials: We recruited 619 healthy Sardinian controls and 182 SARS-CoV-2 patients. Thirty-nine patients required hospital care and 143 were without symptoms, pauci-symptomatic or with mild disease. For all participants, we collected demographic and clinical data and analyzed the HLA allele and haplotype frequencies. Results: Male sex and older age were more frequent in hospitalized patients, none of whom had been vaccinated during the previous seasonal flu vaccination campaignes. Compared to the group of asymptomatic or pauci-symptomatic patients, hospitalized patients also had a higher frequency of autoimmune diseases and glucose-6-phosphate-dehydrogenase (G6PDH) deficiency. None of these patients carried the beta-thalassemia trait, a relatively common finding in the Sardinian population. The extended haplotype HLA-A*02:05, B*58:01, C*07:01, DRB1*03:01 [OR 0.1 (95% CI 0–0.6), Pc = 0.015] was absent in all 182 patients, while the HLA-C*04:01 allele and the three-loci haplotype HLA-A*30:02, B*14:02, C*08:02 [OR 3.8 (95% CI 1.8–8.1), Pc = 0.025] were more frequently represented in patients than controls. In a comparison between in-patients and home care patients, the HLA-DRB1*08:01 allele was exclusively present in the hospitalized patients [OR &gt; 2.5 (95% CI 2.7–220.6), Pc = 0.024]. Conclusion: The data emerging from our study suggest that the extended haplotype HLA-A*02:05, B*58:01, C*07:01, DRB1*03:01 has a protective effect against SARS-CoV-2 infection in the Sardinian population. Genetic factors that resulted to have a negative influence on the disease course were presence of the HLA-DRB1*08:01 allele and G6PDH deficiency, but not the beta-thalassemic trait. Absence of influenza vaccination could be a predisposing factor for more severe disease