Large-Scale Blazar Jets: Clues on High-Energy Emission from Low-Frequency Radio Observations

• Applicant: Professor Dr. Matthias Kadler
• Subject Area: Astrophysics and Astronomy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443220636

More than 100 AGN jets have been imaged with arcsec resolution in the optical and X-ray band. In the case of low-power FR I sources, the X-ray jet emission can generally be interpreted as an extension of the radio synchrotron spectrum. In contrast to this, the radio, optical and X-ray broadband spectra of FR II jets clearly show that other emission processes are at play. Originally, inverse-Comptonization of CMB photons (IC/CMB) was suggested. This model requires bulk relativistic motion on kiloparsec scales (which is difficult to observe) and an electron energy distribution extending down to Lorentz factors smaller than ∼100, which is lower than the energy regimes traced by GHz instruments like the VLA. Very recently, first results of high-resolution LOFAR observations of AGN jets involving international baselines at hundreds of MHz found radio flux densities in one quasar well below the values estimated by extrapolating the GHz spectra and thus falling short of explaining the observed X-ray knot emission in terms of the IC/CMB model. In this project, we will perform a systematic LOFAR study of the long-wavelength radio emission of quasar jets on kiloparsec scales and combine this with shorter-wavelength radioand higher-energy optical and X-ray broadband spectral data to test the IC/CMB and alternative emission models. We will further develop and optimize high-resolution imaging techniques at the low and ultralow radio frequencies in total and linearly-polarized intensity with LOFAR-VLBI techniques to measure magnetic-field geometries and constrain jet-composition and emission models.

• DFG Programme: Research Units
• Subproject of: FOR 5195: Relativistic Jets in Active Galaxies
• International Connection: Ireland
• Co-Investigator: Professor Marcus Brüggen, Ph.D.
• Cooperation Partner: Dr. Shane P. O' Sullivan