The seminar of the Astro & Theory Section takes place Wednesdays in E2-127 (Marie Curie meeting room), starting normally at 14.15. If you would like to suggest a seminar speaker or want to be added to the email list, please contact the organizer (Michael.Kachelriess@ntnu.no).
The (planned) seminars in 2023 are
- 22.02., Alexander van der Horst (George Washington U.): Radio View on Gamma-Ray Burst Extremes
Abstract: Many high-energy astrophysical sources accelerate electrons to extreme velocities, resulting in multi-wavelength emission from synchrotron and other radiation processes. Gamma-ray bursts represent some of the most extreme electron accelerators, in the collimated outflows, or jets, of massive stellar explosions and the mergers of compact objects. Observations of gamma-ray bursts across the electromagnetic spectrum, from GHz radio frequencies to TeV gamma-ray energies, provide a unique probe of electron acceleration due to the relativistic nature of their jets. I will discuss recent developments in this area, both observationally and in modeling the observations, focusing on gamma-ray burst extremes from a radio perspective. - 15.03., Egor Podlesnyi (IFY, NTNU): Modelling the persistent low-state γ-ray emission of the PKS 1510-089 blazar
Abstract: Blazars may accelerate protons and/or nuclei as well as electrons. The hadronic component of accelerated particles in blazars may constitute the bulk of their high-energy budget; nevertheless, this component is elusive due to a high value of the energy threshold of proton interaction with photon fields inside the source. However, broad line regions (BLRs) of some flat spectrum radio quasars (FSRQs) may contain a sufficient amount of matter to render primary protons "visible" in γ rays via hadronuclear interactions. In the present work, we study the persistent γ-ray emission of the FSRQ PKS 1510-089 in its low state utilizing the publicly-available Fermi-LAT data and the spectrum measured with the MAGIC imaging atmospheric Cherenkov telescopes. We find an indication for an excess of γ rays at the energy range ≳20 GeV with respect to a simple baseline log-parabolic intrinsic spectral model. This excess could be explained in a scenario invoking hadronuclear interactions of primary protons on the BLR material with the subsequent development of electromagnetic cascades in photon fields. We present a Monte Carlo calculation of the spectrum of this cascade component, taking as input the BLR photon field spectrum calculated with the Cloudy code.
slides
27.03., Tor Nordam (SINTEF and IFY NTNU): Transport modelling with stochastic differential equations
Abstract: Stochastic transport models have existed at least the early 1900s, when Einstein (1905) and Langevin (1908) published two papers with mathematical models for Brownian motion. Einstein described this as a random displacement process, where a particle moves a distance at during each time interval. Langevin, on the other hand, described a random acceleration process, where a particle changes its velocity by a random amount during each time interval. In this talk, I will give a short historical introduction, and then discuss differences and similarities between the two models.
- 19.04. Enrico Peretti (NBI): Particle acceleration and multi-messenger radiation from astrophysical outflows
Abstract: Winds and outflows are ubiquitous at several scales throughout the Cosmos. They often develop a bubble structure characterized by strong shocks and turbulence where high-energy particles can be efficiently produced. I will present a model in which diffusive shock acceleration is a key process to energize particles in such astrophysical winds.I will show some model applications in the context of young massive stellar clusters, starburst galaxies and active galactic nuclei andI will discuss the associated multi-messenger implications in terms of high-energy photons, neutrinos and escaping cosmic rays.
slides
- 26.04., Mark Kennedy (U Cork): Invisible Monsters and Spider Webs
Abstract: Where is the missing Galactic population of black holes? How do we obtain precise and accurate masses for black holes and neutron stars in our galaxy? These are two of the most pressing questions in astrophysics, and ones which the enormous databases produced by telescopes such as GAIA, the Zwicky Transient Factory (ZTF), and the upcoming Vera Rubin Observatory can help us answer. During this talk, I will discuss where I believe an answer to the missing black hole population may be found. This involves combining data taken by GAIA and ZTF and applying machine learning techniques to find light curves which challenge our understanding of binary classification. I will also highlight the many challenges, pitfalls, and rabbit holes that can be encountered when dealing with these large data sets. I will also give a summary of how the masses of invisible companions can be estimated in these types of binaries, with a focus on some interesting recent results and advances in how the companions in these systems are being modelled.
- 03.05. Jordan Simpson (IFY, NTNU): Cataclysmic variables with HiPERCAM
Abstract: Cataclysmic variables (CVs) are close interacting binary systems consisting of a white dwarf star (primary) accreting matter from a low-mass companion (secondary). As the end-state of many main sequence binaries, and potential progenitors to Type Ia supernovae, CVs form a crucial stage in the evolution of a wide variety of systems. The classical theory of CV evolution has persisted for over 40 years, despite its continuing failures to explain observations. Recently, a new empirical model has emerged that potentially explains many issues in CV evolution - however, a physical basis for this model is still needed. Using the ultra-fast quintuple-band imager HiPERCAM, along with advanced modelling techniques, the team at Sheffield (and collaborators) measures CVs with unprecedented precision to test this new model and ultimately resolve the long-standing problems in CV evolution once and for all.
- 10.05. Alice Harding (LANL): High-energy emission from spider binaries
Abstract: Compact binary systems containing rotation-powered millisecond pulsars with powerful winds that interact with their companions produce shocks that can accelerated particles to very high energies. The pulsar winds also heat and ablate the companion stars, and are appropriately named Black Widow and Redback systems. The Fermi Gamma-Ray Space Telescope has discovered most of the present population of 32 Black Widows and 13 Redbacks. I will discuss the acceleration and radiation from the intrabinary shocks in such systems and present a model for orbitally modulated emission from X-rays to Very-High-Energy gamma-rays.
slides
- 23.05., Mathias Pavely Noedtvedt (IFY, NTNU): ??? Abstract:
- 10.06. Jens Andersen (IFY, NTNU): Pion condensation and pion stars
Abstract: In this talk I will discuss pion condensation in the context of two and three-flavor chiral perturbation theory. I will present results for quark and pion condensates as functions of the isospin chemical potential. The results compare favorably to those of lattice QCD. As an application, I will discuss pion condensation in a dense neutrino cloud and the possibility of pion stars. These are compact objects with a mass up to 20 solar masses and radii of up to 140km.
- tbd: . Kari (IFY, NTNU): ??
Abstract: On
- tbd: . Vittoria Vecchiotti (IFY, NTNU): ??
Abstract: On
- tbd: . Michael Unger (KIT and IFY, NTNU): ??
Abstract: On