5.5 years multi-wavelength variability of Mrk 421: evidences of leptonic emission from the radio to TeV

TL;DR

This study analyzes 5.5 years of multi-wavelength data from Mrk 421, revealing correlated variability in TeV and X-ray bands and independent GeV variations, supporting leptonic emission models and jet dynamics.

Contribution

It provides the longest unbiased multi-wavelength observational campaign of Mrk 421, offering new insights into jet emission mechanisms and variability correlations.

Findings

TeV and X-ray light curves are highly correlated with minimal lag.

GeV emission varies independently and leads long-wavelength variations.

Results support leptonic emission models with dynamic jet conditions.

Abstract

Mrk 421 is a high-synchrotron-peaked blazar featuring bright and persistent GeV and TeV emission. We use the longest and densest ongoing unbiased observing campaign obtained at TeV and GeV energies during 5.5 years with the FACT telescope and the Fermi-LAT detector. The contemporaneous multi-wavelength observations were used to characterize the variability of the source and to constrain the underlying physical mechanisms. We study and correlate light curves obtained by nine different instruments from radio to gamma rays and found two significant results. The TeV and X-ray light curves are very well correlated with lag, if any, shorter than a day. The GeV light curve varies independently and accurately leads the variations observed at long wavelengths, in particular in the radio band. We find that the observations match the predictions of leptonic models and suggest that the physical conditions vary along the jet, when the emitting region moves outwards.