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.
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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): ??
Abstract: I
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- 26.04., Mark Kennedy (U Cork): ??
Abstract: Co
- 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. - 23.05., Mathias Pavely Noedtvedt (IFY, NTNU): ??? Abstract:
- 10.5., Alice Harding (Los Alamos): ??? Abstract:
- xx.yy. Michael Unger (KIT and IFY, NTNU): ??
Abstract: On