Abstract

Poster - Splinter Multimessenger

Friday, 13 September 2024, 15:40   (S25)

TANAMI VLBI Observations of Southern-Hemisphere AGN Associated with High-Energy Emission

Florian Rösch [1,2], Petra Benke [2,1], Philip G. Edwards [3], Florian Eppel [1,2], Jonas Heßdörfer [1,2], Matthias Kadler [1], Roopesh Ojha [4], Eduardo Ros [2], Jompoj Wongphechauxsorn [1]
[1] JMU Würzburg, [2] MPI für Radioastronomie, [3] CSIRO Space and Astronomy, [4] NASA HQ

TANAMI is the only large and long-term VLBI monitoring program focused on the Southern sky aiming at VLBI monitoring of active galactic nuclei (AGN) at X and K band since 2007, and at S band since 2020. The program concentrates on AGN with very high-energy gamma-ray emission and in recent years the source sample has been extended to accommodate the emerging field of neutrino astronomy as well. Recent observational results suggest that high-energy neutrinos may be associated with individual AGN jets which strongly calls for high-quality, high angular-resolution radio observations of neutrino-candidate blazars to study their parsec-scale jet structures. Here, we present first results of S-band observations of TeV blazars and neutrino-candidate blazars in the Southern sky. The complete sample of Southern-hemisphere TeV blazars is dominated by high-peaked BL Lac objects (HBLs). In agreement with other studies of HBLs, we find that these sources have comparatively low core brightness temperatures well below equipartition, in stark contrast to the high Doppler factors typically derived from high-energy studies (Doppler crisis). In the sample of neutrino-candidate blazars, we find both blazars with core brightness temperatures below and above equipartition.