IceCube AGN Neutrino candidate PKS 1717+177: Dark deflector bends nuclear jet

TL;DR

This paper investigates the peculiar, evolving bending of the jet in the AGN PKS 1717+177, exploring potential neutrino emission mechanisms and the influence of an unseen dark object causing the jet's deflection over 23.5 years.

Contribution

It provides the first detailed temporal analysis of jet deviation evolution in PKS 1717+177 and explores multiple scenarios for the jet's complex bending.

Findings

Jet deflection occurs about 0.5 mas from the core and evolves over 23.5 years.

The jet exhibits a periodic brightening near the deviation point.

Multiple mechanisms, including a dark object or black hole interaction, are proposed for jet bending.

Abstract

The BL Lac Object PKS 1717+177 has been identified as potential neutrino-emitting AGN in the point source stacking analysis of IceCube data. We explore peculiarities in the morphology and kinematics of the jet and examine multi-wavelength light curves for distinctive effects which might allow to pinpoint a likely neutrino generation mechanism. We re-modeled 34 high resolution radio interferometric Very Long Baseline Array (VLBA) observations obtained at 15 GHz (between 1999/12/27 and 2023/05/03). A correlation and periodicity analysis of optical KAIT and Tuorla data, as well as for Fermi-LAT $\gamma$-ray data has been performed. The nuclear jet appears deflected and bent at about 0.5 mas distance from the radio core by an encounter with a dark, unseen object. The deviation of the jet evolves over 23.5 years from a simple apparent bend into a significantly meandering structure with increasing amplitude: a zig-zag line. To our knowledge, this is the first time that the temporal evolution of a jet deviation can be traced. The turning point shifts with time and the jet seems to brighten up almost periodically at the point of deviation. The radio core as well as the jet contribute approximately equally to the total flux-density at 15 GHz. We discuss scenarios which could explain the complex jet bending and quasi-regular flaring. We propose that the jet could either be deflected by the magnetosphere of a second massive black hole, by the pressure gradient due to a circumnuclear dense cloud, or via gravitational lensing by an intervening black hole.