PlasmaAstro-TOK-Seminar 2024
 

Abstract: Active Galactic Nuclei (AGN) are among the most powerful persistent particle accelerators in our universe. They have been studied for more than half a century, but they are still far from being understood. The advent of new instrumentation for photon and neutrino astronomy brings new perspectives that are starting to help out unraveling the insights of these powerful cosmic accelerators. Among all AGNs, the best candidates to probe the evolution of the particle distribution are the those that are nearby and bright throughout the electromagnetic spectrum. We will present results from extensive multi-instrument observations of a few bright and nearby AGNs and will discuss the complexity in the temporal evolution of the broadband emission. These MWL data can be used to derive particle populations under certain model assumptions, and the next step is to validate these models (and the related dynamics) with dedicated simulations for particle acceleration and temporal evolution. [mehr]

Abstract: After the IceCube Neutrino Observatory discovered an isotropic flux of high-energy astrophysical neutrinos, the next fundamental question arose, “Where are these neutrinos coming from?” After a decade, we have now started having our first answers, and neutrino astronomy is emerging among the major players in the multimessenger paradigm. The blazar TXS 0506+056 and the Seyfert galaxy NGC 1068 are the first candidates as extragalactic neutrino sources. Even though they are both AGN powered by a supermassive black hole, they inhabit different regions of the neutrino energy spectrum, with TXS 0506+056 showing a hard spectral emission around the PeV and NGC 1068 exhibiting a softer spectrum at ~1-15 TeV. This suggests that more than one population of accelerators might produce the observed isotropic cosmic neutrino background. In this seminar, I will outline the challenges faced by the searches for neutrino point-like sources with IceCube. I will give an overview of the latest results from searches trying to identify more neutrino sources among blazars and Seyfert galaxies and how much these two populations of sources could contribute to the total neutrino flux observed by IceCube. [mehr]

Abstract: Being located at only ~8 kpc from us, the center of our Galaxy provides us with the unique opportunity to study the physics occurring in the core of normal galaxies at very high spatial resolution. Thanks to its penetrating power, the X-ray band is particularly suited for studies of the Galactic center, allowing us to have a direct view of the central heart of the Milky Way. At the center of this stage, the accretion onto Sgr A*, the supermassive black hole at the Galactic center, is observed to currently produce very low luminosity. In this talk I will discuss the recent multi-wavelength campaigns to study the current emission from Sgr A* as well as the evidence in favour of a period of more luminous activity, just a few centuries ago. [mehr]

Abstract: UHECRs at the most extreme energies provide strong constraints on their possible sources. We propose to use the reconstructed properties of individual detected UHECRs to map out three-dimensional constraints on the locations of their unknown sources. We focus on the Amaterasu particle detected by Telescope Array and use CRPropa3 to model all relevant propagation effects, including deflections in the Galactic and extra-Galactic magnetic fields. We consider key input quantities such as distance, position, and energy as free parameters. We use Approximate Bayesian Computation (ABC) to derive constraints on the source locations for this event and demonstrate the impact of uncertainties in the reconstructed UHECR properties on these results. We also highlight possible astrophysical sources that are compatible with these regions and requirements. This complementary perspective serves as a foundation for building more physically-motivated source catalogues and statistical analyses in the future. [mehr]

Abstract: In this talk I share recent results from leptohadronic modeling of 32 BL Lac objects coincident with IceCube high-energy neutrino alert events. Using a newly released open-source cosmic-ray simulation software, we have built a robust physical framework that can simultaneously describe multi-wavelength observations and IceCube point source data. This provides new constraints on the source environment, including the position of the gamma-ray emitting region and the elusive role of broad line emission in masquerading BL Lacs. I discuss future paths for tackling open questions on time-domain hadronic signatures, IceCube data interpretation, and cosmic ray acceleration. [mehr]

Abstract: I will discuss the source-propagation modeling of ultra-high-energy cosmic rays (UHECR) and diffuse neutrinos from the Tidal Disruption Event (TDE) population. This model builds on neutrino production models of three TDEs that may be associated with IceCube alerts. I will extend this discussion to a population model of neutrino- and UHECR-emitting TDEs, exploring their roles in the origin of ultra-high-energy cosmic rays and diffuse neutrinos. This talk will also address the current challenges and future directions in source-propagation modeling, and the potential impact of upcoming facilities like Auger Prime and future EeV neutrino observatories. [mehr]

Abstract: Cluster mergers serve as powerful laboratories for cosmology and astrophysics. Radio relics, diffuse radio emissions found in the outskirts of merging clusters, are believed to originate from shock acceleration by cluster merger shocks. In this talk, we will demonstrate the use of cluster mergers exhibiting radio relics to study plasma acceleration and the nature of dark matter. Utilizing high-quality multi-wavelength observations and numerical simulations, including idealized simulations and the cosmological zoom-in simulation TNG-Cluster, we will show how radio relics can constrain the merger history of galaxy clusters. We will explore the implications of radio relics in verifying the self-interacting nature of dark matter. Additionally, our numerical simulations indicate that high acceleration efficiency is required to explain the observed luminosity of radio relics. We will present our recent MeerKAT observations to discuss the role of cluster AGN activity in mitigating the low acceleration efficiency of cluster merger shocks. [mehr]

Abstract: Studies of super-strongly magnetized plasmas play a crucial role in astrophysics and laboratory experiments, demanding a better understanding of how quantum electrodynamic (QED) effects influence plasma behaviour. Previous theoretical works have shown that QED effects cause significant modifications to plasma behaviour around Magntars using analytical and semi-analytical calculations. In this work, we developed a numerical method that advances the QED vacuum polarization effects in the particle-in-cell (PIC) kinetic method by introducing a new field solver method of the non-linear Maxwell equations. We showed that the electromagnetic waves in simulations follow the analytical solutions well for the birefringence effects between the O- and X-mode polarized waves with increasing magnetic field intensity. This new QED-PIC simulation framework will be applied to model electromagnetic fields in magnetar magnetospheres. [mehr]