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- 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.
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- 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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