A recent study published in The Astrophysical Journal has revealed the physical picture of magnetically driven shocks deep within the jet of blazar 1156+295, finding that the release of magnetic energy within the jet precedes radio flares and the inferred magnetic flux can reach the theoretical threshold of a magnetically arrested disk (MAD) — evidence that powerful AGN jets are magnetically driven from their very core.

The study was conducted by XU Wancheng, a Ph.D. student at the Xinjiang Astronomical Observatory (XAO) of the Chinese Academy of Sciences, under the supervision of Prof. CUI Lang.

In the vast depths of the universe, blazars, with their extreme relativistic jets pointing directly at Earth, act as cosmic energy hubs connecting supermassive black holes to the vast cosmic environment. However, the physical drivers and radiation mechanisms behind these plasma outflows, which are launched outward at nearly the speed of light, have long remained a core puzzle to solve in modern high-energy astrophysics.

To tackle the question, the researchers conducted an analysis of the radio flaring periods of 1156+295 using multi-frequency monitoring data from the 100-meter Effelsberg radio telescope in Germany and multi-epoch images from Very Long Baseline Interferometry (VLBI).

Through synchrotron self-absorption (SSA) spectral modeling, the researchers extracted the spectral turnover frequency and turnover flux density. By combining these with the core size and brightness temperature derived from quasi-simultaneous VLBI images, they quantitatively reconstructed the long-term evolutionary trajectories of the jet's magnetic field strength and magnetic flux.

The results showed that the blazar's radio variability, fine structural evolution of the jet, SSA spectral variations, and inner-jet magnetic field properties exhibit a high degree of temporal connection and physical coupling.

The researchers then combined these results with theoretical models. They found that the release of magnetic energy within the jet precedes the radio flares, and that the inferred magnetic flux can reach the theoretical threshold of a MAD. This series of multi-level dynamic physical processes is highly consistent with the theoretical expectations of the magnetically driven jet scenario and the shock-in-jet model.

This study places the radio variability, magnetic field measurements, spectral evolution, and inner-jet structural dynamics of the blazar onto a common timeline framework, providing crucial observational evidence for understanding the launching, energy transport, and driving mechanisms of powerful jets in active galactic nuclei (AGNs), the researchers said.

Furthermore, it highlights the great value of combining multi-frequency single-dish monitoring with high-resolution, multi-epoch VLBI observations in exploring the "magnetic engines" of AGN jets and their extreme plasma processes, they added.