On the possible core shift break in relativistic jets

TL;DR

This paper investigates the potential for a core shift break in relativistic jets, which can reveal details about jet geometry, magnetic fields, and plasma acceleration, demonstrated through application to NGC 315.

Contribution

It introduces a method to identify core shift breaks related to jet geometry transitions and applies it to observational data from NGC 315.

Findings

Identified conditions for core shift offset jumps due to geometry changes

Applied the method to NGC 315 to detect a core shift break

Suggested plasma heating mechanisms can also cause different types of core shift breaks

Abstract

Measurement of a jet geometry transition region is an important instrument of assessing the jet ambient medium properties, plasma bulk motion acceleration, parameters of a black hole and location of a jet launching radius. In this work we explore the possibility of a presence of a core shift break, associated with the geometry and jet physical properties transition. We obtain the relations on the core shift offset jump due to a change in a core shift exponent. The condition of a proper frame magnetic field continuity and the core shift break can be used as an instrument to refine the magnetic field estimates upstream the break. This method is applied to the jet in NGC 315. We speculate that the localised in a flow plasma heating either by reconnection or due to particles acceleration at the shock will also lead to a core shift break, but of a different type, than the one observed in NGC 315. We propose to use the multi-frequency core shift measurements to increase the number of sources with a detected jet shape break and to boost the accuracy of assessing the properties of a jet geometry transition region.