TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry

Abstract

Context. TANAMI is a multiwavelength program monitoring active galactic nuclei (AGN) south of − 30° declination including high-resolution very long baseline interferometry (VLBI) imaging, radio, optical/UV, X-ray, and γ-ray studies. We have previously published first-epoch8.4 GHz VLBI images of the parsec-scale structure of the initial sample. In this paper, we present images of 39 additional sources. The full sample comprises most of the radio- and γ-ray brightest AGN in the southern quarter of the sky, overlapping with the region from which high-energy (> 100 TeV) neutrino events have been found. Aims. We characterize the parsec-scale radio properties of the jets and compare them with the quasi-simultaneous Fermi/LAT γ-ray data. Furthermore, we study the jet properties of sources which are in positional coincidence with high-energy neutrino events compared to the full sample. We test the positional agreement of high-energy neutrino events with various AGN samples. Methods. TANAMI VLBI observations at 8.4 GHz are made with southern hemisphere radio telescopes located in Australia, Antarctica, Chile, New Zealand, and South Africa. Results. Our observations yield the first images of many jets below − 30° declination at milliarcsecond resolution. We find that γ-ray loud TANAMI sources tend to be more compact on parsec-scales and have higher core brightness temperatures than γ-ray faint jets, indicating higher Doppler factors. No significant structural difference is found between sources in positional coincidence with high-energy neutrino events and other TANAMI jets. The 22 γ-ray brightest AGN in the TANAMI sky show only a weak positional agreement with high-energy neutrinos demonstrating that the > 100 TeV IceCube signal is not simply dominated by a small number of the γ-ray brightest blazars. Instead, a larger number of sources have to contribute to the signal with each individual source having only a small Poisson probability for producing an event in multi-year integrations of current neutrino detectors.

Gamma-ray flares and broadband spectral study of PKS 0402-362

“…A dominant accretion disk is observed for this source which is well fitted by the combination of synchrotron and the thermal disk emission (see . This source has a strong accretion disk as it was also observed by Müller et al (2018) (see there Figure A.2) which makes this source a good candidate to explore the disk-jet connection, which is out of scope for this paper. As we discussed earlier that the emission region is located at the boundary of the BLR, therefore, it can provide seed photons for the external Compton (EC).…”

Very long baseline interferometry observations of the high-redshift blazar candidate J0141–5427

“…This is especially true at lower frequencies, as indicated by the high rate of fringe-fit solutions found for J0141-5427 in our experiment at 1.7 GHz. So far, VLBI imaging surveys of low-declination southern radio AGN have mainly concentrated on bright sources with at least ∼100 mJy flux densities (e.g., Shen et al 1997Shen et al , 1998Ojha et al 2004Ojha et al , 2005Ojha et al , 2010Müller et al 2018).…”