Speaker
Description
Markarian 421 is the brightest high-frequency-peaked BL Lac (HBL) observed in X-rays and gamma rays. Its radio jet, observed at a resolution below milliarcsecond with the VLBA, shows four stationary components. Interpreting these components as four stationary shocks, a distinct variability pattern is expected to be observed each time a strong perturbation propagates through the jet. Such a repeating pattern has previously been noticed in X-rays with a significance above 3 standard deviations. Preliminary results of a similar study applied to gamma-ray data will be shown, combining long-term very-high-energy datasets from VERITAS and FACT; results from Fermi-LAT observations and a 2020 radio VLBA campaign will also be presented. Finally, some of the implications of successive shocks in our current view of AGN jets emission and particle acceleration will be discussed.
