On Lorentz Variability of Magnetically Dominated Relativistic Outflows

Abstract

In this Letter, we show that magnetized relativistic outflows can exhibit a relativistic effect in which Lorentz transformation maps magnetic field topology into apparent temporal variability in the observer's frame. Using a force-free Beltrami configurations as representative equilibria of magnetically dominated outflows, we demonstrate that Lorentz mapping of stationary helical magnetic field produces quasi-periodic modulation of observable electromagnetic signatures, without invoking intrinsic plasma variability. This effect may be described as an aberration of force-free magnetic fields under Lorentz transformation. The characteristic frequency of the time variability is determined by the helical wave-number of the magnetic field, the viewing angle, and the bulk Lorentz factor of the jet outflow, and scales linearly with $Γ$. This establishes a purely kinematic relativistic origin of variability and introduces the concept of magnetic Lorentz seismology: the inference of magnetic field structure in relativistic outflows directly from observed temporal variability.

Figures (1)

• Figure 1: Schematic illustration of the coordinate systems used in the analysis. The system $(X,Y,Z)$ sets the observer’s lab frame, with the observer (line of sight) located along the $Z$-axis. The jet lies in the plane perpendicular to the $X$-axis and is inclined by an angle $\theta$ to the line of sight. The primed frames $(X^\prime,Y^\prime,Z^\prime)$ and $X^{\prime \prime},Y^{\prime \prime},Z^{\prime \prime}$ are co-moving coordinate systems, with $Z$ and $Z'$ axes aligned with the line of sight and $Z"$ axis with the jet flow direction, respectively.