Landing page for project EE010

We are currently entering a new era in high-energy astrophysics. While current imaging air Cherenkov telescopes (MAGIC, H.E.S.S., and VERITAS) have already detected ~90 Active Galactic Nuclei at TeV energies, the upcoming Cherenkov Telescope Array Observatory (CTAO) will greatly expand the accessible energy range - from tens of GeV to hundreds of TeV. A key open question remains: Where in the jet, and by what mechanisms, are TeV gamma-rays produced? Theoretical models predict distinctive jet morphologies, such as standing recollimation shocks or spine-sheath structures. To test these predictions, we propose a systematic VLBI imaging campaign targeting all Northern Hemisphere high-frequency-peaked BL Lac objects (HBLs) - the most abundant TeV-emitting blazar class. Utilizing the superior sensitivity and resolution of the EVN at 8 GHz, we will search for characteristic jet features both in total intensity and polarization. Our goal is to uncover common structural traits possibly linked to TeV emission. Furthermore, we will statistically compare the jet properties of these HBLs to those of low-frequency-peaked BL Lacs observed at the same frequency by the TANAMI program. This study will provide critical constraints on the physical conditions enabling TeV emission in blazar jets.

This data is part of the archive of VLBI data maintained by JIVE on behalf of the EVN, a network of radio telescopes located primarily in Europe and Asia, with additional antennas in South Africa. The EVN archive itself has the DOI https://doi.org/10.17616/R3Z197