Synchrotron Self-Absorption Spectral Modeling Reveals a Magnetically Driven Shock-in-Jet Scenario in Blazar 1156+295

TL;DR

This study uses synchrotron self-absorption spectral modeling combined with VLBI data to analyze the magnetic field and jet dynamics in blazar 1156+295, supporting a magnetically driven shock-in-jet scenario during flares.

Contribution

It introduces a comprehensive approach combining SSA spectral modeling and VLBI measurements to investigate magnetic fields and jet evolution in blazars, providing new observational evidence for a magnetically driven jet mechanism.

Findings

Magnetic flux reaches or exceeds MAD threshold during flares.

Radio flux and spectral evolution align with shock-in-jet models.

Magnetic energy release precedes radio flares.

Abstract

Unveiling the launching and driving mechanisms of powerful jets in active galactic nuclei (AGNs) is crucial for understanding the co-evolution of supermassive black holes (SMBHs) and their host galaxies. 1156+295 is a blazar at a redshift of z=0.729 and exhibits significant variability in long-term radio monitoring. Using multi-frequency Effelsberg single-dish flux density data from 2007 to 2012, we performed synchrotron self-absorption (SSA) spectral modeling and extracted the turnover frequency and turnover flux density. By combining SSA spectral modeling with the core size and brightness temperature from quasi-simultaneous very long baseline interferometry (VLBI) images, we estimated the jet magnetic-field strength and magnetic flux, and investigated their temporal evolution in 1156+295. The evolution of radio flux density, spectral shape, and jet structure is consistent with the shock-in-jet framework. The inferred magnetic flux reaching or exceeding the magnetically arrested disk (MAD) threshold, together with evidence that magnetic energy release precedes the radio flares, supports a magnetically driven jet scenario. Overall, our results place magnetic-field measurements, spectral evolution, and inner-jet structural changes on a common timeline, providing observational constraints on their coupled evolution during flares.