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arXiv · 2608.10067

Decoding the jet of BL Lacertae using relativistic magneto-hydrodynamics

G. F. Paraschos·J. A. Kramer·I. Liodakis·S. G. Jorstad·A. P. Marscher·I. Myserlis·I. Agudo·N. R. MacDonald
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Abstract

Blazars are a highly variable subclass of active galactic nuclei, whose relativistic jet is pointed towards our line of sight at a small angle. Their variability is often characterised by multi-band flares. BL Lacertae (BL Lac), the namesake of a blazar subclass recently exhibited the highest recorded linearly polarised optical flare. We investigate the origin of this flare via very-long-baseline interferometry observations. Our analysis shows that the sweeping, helical motion of the BL Lac jet, which is known to exhibit kink-like instabilities, can explain the observed flux density spike and polarisation angle rotation, as also confirmed by our state-of-the-art relativistic magneto-hydrodynamic simulations. As a by-product of these simulations we find that baryon loading of the jet is required to optimally replicate the observed jet morphology.

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G. F. Paraschos, J. A. Kramer, I. Liodakis, S. G. Jorstad, A. P. Marscher, I. Myserlis, I. Agudo, N. R. MacDonald. 2026-08-10. Decoding the jet of BL Lacertae using relativistic magneto-hydrodynamics. https://arxiv.org/abs/2608.10067

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