Project Description
After the successful detection of cosmic high-energy neutrinos (Aartsen et al., 2013), the field of multiwavelength photon studies of active galactic nuclei (AGN) is entering an exciting new phase. The first hint of a possible neutrino signal from the blazar TXS 0506+056 (Aartsen et al., 2018) and 3 hints on signals from the catalog of extragalactic point sources as well as the Seyfert NGC 1068 (Carver & IceCube Coll. (incl. W. Rhode and J. Becker Tjus), 2019) leads to the anticipation that AGN will soon be identified as point sources of high-energy neutrino radiation, representing another messenger signature besides the well-established photon signature. In this project, we will bring together theoretical calculations and long-term observations in gamma-ray and neutrino data. In doing so, we will develop time-dependent models for leptonic, hadronic, and lepto-hadronic scenarios. In this project, we will have a special focus on the effect of high-density environments: in the core of active galaxies, where acceleration is believed to be highly efficient, both gas and photon densities can be extreme: the accretion disk produces a large photon field and the particles can meet high gas densities in scenarios where a star is swallowed by the jet, as well as in tilted-jet scenarios where the jet runs into the dense material of the torus. For the emission of photons and neutrinos, these effects are of high relevance, as photons can be absorbed via comptonization or gamma-gamma, and neutrinos might be produced via the decay of prompt hadrons, because the pions and kaons which produce neutrinos in thin environments can interact before they decay. Test scenarios for the different source classes will be defined in the theoretical part of the project and tested with observational data using two different approaches:
- We will investigate the brightest TeV blazars to test the leptonic scenario.
- We will use a sample of blazars associated with neutrinos to compare the measured long-term time behavior of the multiwavelength light curve with the predicted templates for the hadronic, leptohadronic, and leptonic scenarios in order to quantify a correlation.
As long as the sensitivity depends on continued data-taking with the present IceCube detector, search strategies based on a combination of dedicated predictions and statistical searches have to be developed. The present generation of ground-based air Cherenkov telescopes such as H.E.S.S., MAGIC, and VERITAS has detected more than 60 AGN as powerful variable TeV photon emitters. Most of them belong to the class of blazars, which is characterized by rapid time variability at all wavelengths. Often these objects show superluminal motion components at radio and mm frequencies. With the FERMI/GLAST satellite, data at lower gamma-ray energies and contemporaneous observations at radio to X-ray photon frequencies, spectral photon energy-flux distributions at different times, as well as photon light curves at different frequencies of unprecedented detail and accuracy are available. These allow us to perform crucial tests of our current understanding of the physical processes responsible for the generation of photon and neutrino radiation in these sources as correlations and anti-correlations between the messengers at their measured energies changing on the specific timescales. The experimental data situation will improve during the runtime of the proposed CRC at least by the completion of CTA and IceCube-Gen2.
